Cancer Flashcards
1
Q
Define metaplasia
A
A reversible change in which one adult cell type (usually epithelium) is replaced by another cell type - an ADAPTIVE process.
2
Q
Define dysplasia
A
An abnormal pattern of growth in which some of the cellular and architectural features of malignancy are present.
Pre-invasive stage: intact basement membrane.
Cells appear darker (hyperchromatic) due to enlarged nuclei which increase the nuclear: cytoplasmic ratio.
3
Q
What is high grade dysplasia?
A
More likely to progress and less likely to spontaneously regress than low grade dysplasia.
4
Q
Define neoplasia
A
An abnormal, autonomous proliferation of cells unresponsive to normal growth control mechanisms.
5
Q
Define lesion and tumour.
A
A lesion is a zone of tissue with impaired function due to damage from disease or wounding. A tumour is any kind of mass-forming lesion.
6
Q
Give differences between benign and malignant tumours.
A
Benign tumours do not invade and do not metastasise. This is the key functional difference.
Descriptive (not diagnostic) markers of a benign tumour are that it is encapsulated, well differentiated, slow growing and has normal mitoses.
7
Q
When might a benign tumour be fatal?
A
If it is in a dangerous place (pituitary, meninges), secretes something dangerous (insulinoma), gets infected (bladder), bleeds (stomach), ruptures (liver adenoma) or torts (ovarian cyst).
8
Q
How do we name benign epithelial tumours?
A
If it is a tumour of surface epithelium, such as skin and the bladder, it is a PAPILLOMA
A benign tumour of glandular epithelium is an ADENOMA.
9
Q
What is a carcinoma?
A
A malignant tumour derived from EPITHELIUM.
E.g. squamous cell carcinoma, adenocarcinoma, basal cell carcinoma, transitional cell carcinoma.
10
Q
What is the nomenclature for benign and malignant tumours of soft tissue (connective tissue).
A
Benign = add -oma (osteoma) Malignant = SARCOMA, e.g. osteosarcoma.
11
Q
Contrast rhabdomyosarcoma and leiomyosarcoma.
A
Rhabdomyosarcoma is a malignant tumour of striated muscles cells.
Leiomyosarcoma is a malignant tumour of smooth muscle cells.
12
Q
Contrast lymphoma and leukaemia.
A
Leukaemia is a malignant tumour of bone marrow derived cells circulating in the blood.
Lymphoma is a malignant tumour of lymphocytes in lymph nodes.
Note benign Leukaemias and lymphomas are extremely uncommon and hence the nomenclature.
13
Q
Define teratoma.
A
A tumour derived from germ cells, which has the potential to develop into tumours of all 3 germ layers.
Gonadal teratomas in males are all malignant; in females mostly benign.
14
Q
Define hamartoma.
A
Localised overgrowth of cells and tissues native to the organ. Cells are mature but architecturally abnormal. Common in children, but usually stop growing when they do.
15
Q
What is a tumour which performs none of the usual roles of the tissue it is derived from described as?
A
An anaplastic carcinoma.
16
Q
What is the assessment of the differentiation of a tumour based on?
A
Evidence of presence of normal functioning, e.g. production of keratin, bile, mucin, hormones.
17
Q
How are grade and stage related to prognosis?
A
Grade (degree of differentiation) correlated with stage (high grade = low differentiation). But stage (TNM) more important in prognosis.
18
Q
Describe poorly differentiated cells.
A
They have larger nuclei (and hence a higher nuclear-cytoplasmic ratio) and more mitoses than the normal tissues they are derived from. They may have abnormal mitoses (e.g. tripolar) and marked nuclear pleomorphism (variability in nuclear size and shape).
19
Q
At what stage of the cell cycle are cells most vulnerable?
A
M phase (mitosis) - the cells are more easily killed, the DNA damage is irreparable and gene transcription is silenced at this phase.
20
Q
Describe the centrosome.
A
An organelle which consists of 2 centrioles at 90 degrees to each other. The centrioles consist of barrels of 9 triple microtubules.
It functions as the microtubule organising centre (MTOC) and forms the mitotic spindle in mitosis.
21
Q
Describe prophase.
A
Chromatin condenses - each condensed chromosome consists of 2 sister chromatids. Each chromatid is associated with a kinetochore.
2 sister chromatids linked by a centromere.
22
Q
Describe late prophase.
A
Duplicated centrosomes migrate to opposite sides of the nucleus and organise the assembly of spindle microtubules.
Mitotic spindle forms outside the nucleus between the 2 centrosomes.
Radial microtubule arrays (ASTERS) form around each centrosome (MTOC) - the radial arrays meet and form polar microtubules
23
Q
What happens in prometaphase?
A
Nuclear membrane breaks down.
Attachment of chromosomes to spindle via kinetochores
Microtubules from opposite pole is captured by sister kinetochore.
Chromosomes attached to each pole congress to the middle. They slide rapidly along microtubules towards the middle.
24
Q
Describe metaphase.
A
Chromosomes aligned at equator of spindle - attached by their kinetochores.
25
Describe anaphase.
Paired chromatids separate to form 2 daughter chromosomes.
Cohesin holds 2 sister chromatids together.
In anaphase A - cohesin breaks down, and daughter chromosomes are pulled towards opposite spindle poles.
In anaphase B - the daughter chromosomes migrate towards poles, and the poles (centrosomes) themselves move apart.
26
Describe telophase.
Daughter chromosomes arrive at centrosome.
Nuclear envelope reassembles at each pole.
Assembly of contractile ring.
27
Describe cytokinesis.
Acto-myosin contractile ring contracts.
New membrane inserted.
Midbody begins to form.
Nucellar structures reform, chromatin decondenses
28
Describe the spindle assembly checkpoint at the transition out of metaphase.
Required CENP-E (centromere protein E) and BUB proteins.
BUBs dissociate from kinetochore when chromosomes are properly attached to the spindle - when all are dissociated, anaphase proceeds.
hence serves to sense completion of chromosome alignment and spindle assembly.
29
How can the transition out of metaphase lead to aneuploidy?
Misattachment of microtubules to kinetochores.
Syntelic attachment : both microtubules go towards same daughter cell.
Monotelic = only 1 chromatid attached.
Merotelic = multiple microtubules attached to one kinetochore (this chromosome is lost at cytokinesis).
30
Give another cause of aneuploidy - other than misattachment of microtubules.
Aberrant centrosome/ DNA duplication.
31
How do checkpoint kinase inhibitors work as anti-cancer therapy?
They induce gross chromosomal mis-segregations by inhibiting attachment error-correction mechanisms.
They target checkpoint kinases (CHEK1 and CHEK2), which work at the G2 phase of the cell cycle to check fidelity of DNA replication.
32
How do taxanes and vinca alkaloids work as anti-cancer therapy?
They alter microtubule dynamics, producing unattached kinetochores and causing long-term mitotic arrest.
Vinca alkaloids inhibit assembly of mitotic microtubules whereas taxanes inhibit disassembly.
33
What effect can a tumour have on different checkpoints in the cell cycle?
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In the absence of stimulus, a cell enters G0, exits the cell cycle and dismantles its cell cycle apparatus. This can be blocked.
Also, G1 checkpoint (growth factors) can be enhanced,
G2 checkpoint (DNA damage) can be suppressed
Metaphase checkpoint (sister chromatid alignment) can be suppressed.
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34
How are signalling cascades stimulated?
In the presence of a ligand, receptors form dimers. These cause phosphorylation at kinase domains. Activates proteins (causes change in shape or creates docking site for another protein). Amplifies signal.
35
Briefly describe cytotoxic chemotherapy.
Given i.v. or orally. Systemic. Non-targeted (all rapidly dividing cells affected).
Pre-op = neoadjuvant
Post-op = adjuvant
Can be monotherapy or combination, with curative or palliative intent.
36
Describe alkylating agents.
A group of drugs given as cytotoxic chemotherapy which add alkyl groups to guanine residues in DNA, leading to cross-linking of DNA strands and prevention of DNA uncoiling at replication.
They trigger apoptosis.
They encourage mis-pairing, and as such are oncogenic and risk secondary malignancy.
Example = chlorambucil.
37
Describe pseudo-alkylating agents.
A group of drugs given as cytotoxic chemotherapy which add platinum to guanine residues in DNA.
Same mechanism of cell death as alkylating agents.
Example = CISPLATIN!!!!, carboplatin.
38
Describe anti-metabolites.
A group of drugs given as cytotoxic chemotherapy which masquerade as purine or pyridine residues leading to inhibition of DNA synthesis: DNA double strands breakdown and cells apoptose.
39
Describe anthracyclines.
A group of drugs given as cytotoxic chemotherapy which inhibit transcription and replication by inserting between nucleotides within DNA/RNA.
They block DNA repair (are mutagenic) and create damaging free radicals.
Examples = doxorubicin.
40
Describe topoisomerase inhibitors.
A group of drugs given as cytotoxic chemotherapy which induce temporary breaks in the DNA backbone (since topoisomerase needs to prevent DNA torsional strain).
41
How can tumour cells become resistant to cytotoxic chemotherapy?
Enhanced DNA repair, drug effluxed from the cell by ATP-binding cassette transporters, DNA adducts replaced by Base Excision Repair.
42
Why are dual-kinase inhibitors used?
Since inactivating one pathway in monogenic cancers can activate parallel pathways or feedback cascades.
Dual-kinase inhibitors prevent feedback loops but increase toxicities
43
Give 6 hallmarks of cancer cells.
Self-sufficient (sustains proliferative signalling), insensitive to anti-growth signals, anti-apoptotic, pro-invasive and metastatic, proangiogenic and non-senescent.
44
How are monoclonal antibodies used as anticancer therapy?
They target extracellular components of receptors and neutralise the ligand, prevent receptor dimerisation and cause receptor internalisation.
45
How do small molecule inhibitors work as anti-cancer therapy?
Bind to the kinase domain of the tyrosine kinase within the cytoplasm to block autophosphorylation and downstream signalling.
E.g. glivec.
46
Why are targeted therapies (monoclonal antibodies and small molecule inhibitors) good and how does resistance arise?
By acting on receptors, targeted therapies block cancer hallmarks without the toxicity observed with cytotoxics.
Resistance can arise from mutations in the ATP-kinase domain, intrinsic resistance, intragenic mutations and upregulation of downstream or parallel pathways.
47
What is a protein domain?
A functional and structural unit copied in many proteins. Some domains are important in molecular recognition: no enzymatic action, simply bring proteins together.
48
Describe the MAPK (mitogen-activated protein kinase) cascade.
EPG causes epidermal growth receptor dimerization and cross-phosphorylation at the cytoplasmic domain. Adaptor protein, Grb2 binds, associated with sos at SH3 domains. Sos causes RAS to be activated by displacing GDP for GTP. RAS activates Raf (MAPKKK), which activates MEK (MAPKK), which activates ERK (MAPK). ERK activates cMyc, a transcription factor which promotes cyclin D transcription. Cyclin D binds to Cdk4/6: this cyclin/Cdk complex binds to Rb to phosphorylate it (inactivated), releasing E2F (another transcription factor) which is involved in transcribing further cyclin, initially cyclin E.
49
Give 4 proto-oncogenes in the MAPK pathway.
RAS: can mutate so that GAP (GTPase activating protein) binding is prevented, or so GTP hydrolysis is prevented, resulting in a constitutively active RAS.
cMyc - overexpressed in many tumours.
Cyclin D - overexpressed in 50% of breast tumours.
Epidermal growth factor receptor - can be mutationally active or overexpressed, e.g. HER2.
50
Describe briefly the cyclin-dependent kinase (Cdk)/ cyclin control of the cell cycle.
Cell cycle control based on cyclically active protein kinases. The Cdks are present all the time: cyclins are transiently expressed at specific points of the cell cycle. They are synthesised then degraded.
Activated (phosphorylated) Cdks phosphorylate proteins drive cell cycle progression.
Cdk 4/6, 2, 2, 1; cyclin D, E, A ,B.
Stimulate synthesis of proteins required for next stage.
51
Describe the tumour suppressor protein Rb.
pRb binds to transcription factor E2F in G0 of the cell cycle. It inactivates the TF. Cdk4/6-cyclin D phosphorylates pRb, releasing E2F.
It then causes gene transcription, e.g. cyclin E, needed for the next phase of the cell cycle.
Cdks phosphorylate pRb at different sites to cause transcription of different genes.
52
Describe Cdk inhibitors (CKIs).
CKIs must be degraded to allow cell cycle progression.
INK4 family = G1 phase CKIs. They displace cyclin D.
CIP/KIP family = S phase CKIs. Inhibit all Cdks by binding to whole Cdk/cyclin complex.
CKIs are tumour suppressors.
53
Give 2 tumour suppressor genes in the MAPK pathway.
pRb - inactivated in many cancers.
| KIP - under-expression correlated with poor prognosis in malignancies.
54
Describe the PI3'K-Akt pathway.
Ligand binds - receptor dimerises. Adapter protein is PI3'k (a lipid) which causes PIP2 to be phosphorylated to PIP3 - resulting in PDK-1 activation which activates PKB/Akt.
PKB/Akt phosphorylates and inactivates caspase 9.
they also phosphorylate and inactive Bad, so Bcl2 is free to bind to Bak and Bax.
they bind to and phosphorylate the transcription factor FOXO, so it is inactivated. FOXO transcribes apoptotic proteins, such as caspase 9, and cell-cycle arresting proteins (KIP).
55
Describe PTEN.
A tumour suppressor phosphatase which dephosphorylates PIP3 to PIP2, resulting in less activation of PKB/Akt. PTEN promotes cell survival.
56
How can cytosine be converted to form uracil (the RNA equivalent of thymine)?
Can be deaminated to form uracil relatively easily.
| 5-methyl cytosine can be deaminated to form thymine directly.
57
What is an adduct?
A larger molecule attached to DNA.
58
Describe how radiation in the form of UV light can damage DNA.
UV absorbed by nucleic acids with the resulting influx of energy inducing chemical changes. Most frequently, bonds are formed between pyrimidines, particularly thymine. Results in thymine dimers.
59
What sort of changes do oxygen free radicals cause on DNA?
They cause double and single strand breaks, leading to apurinic and apyrimidic sites: "nicks" or "gaps".
60
What is p53?
A tumour suppressor gene which is the "guardian of the genome". It regulates cell cycle and conserves genomic stability by preventing mutation.
It responds to a wide variety of insults.
Regulates target genes, including DNA repair pathways.
61
Describe direct repair of DNA.
Direct repairs involve the reversal of the damage, e.g. photolyases repair thymine dimers.
62
Compare base excision repair (BER) and nucleotide excision repair (NER).
In BER, the base has been damaged by a mutagen. The base is removed by DNA-glycolase.
Endonucelase splits the phosphodiester backbone.
Polymerase adds a new base.
The backbone is ligated by DNA ligase.
In NER, a larger molecule, an adduct, has been added. The endonuclease makes a nick. Helicase removes the area. Polymerase adds new nucleotides, before ligase connects the backbone.
63
What are the consequences of DNA damage?
3 outcomes:
Efficient repair --> normal cell
Apoptosis --> cell death.
Incorrect repair --> DNA replication with fixed mutations leading to aberrant proteins or, if crucial targets mutated, carcinogenesis.
64
When would programmed cell death (PCD) be required?
Harmful cells (viral infection, DNA damage).
Developmentally defective (B-lymphocytes expressing self-antibodies).
Excess/unnecessary cells.
Obsolete cells (mamillary epithelium at the end of lactation).
Exploitation - chemotherapeutic killing of cells.
65
Contrast necrosis and apoptosis.
Necrosis is unregulated cell death, associated with trauma, cellular disruption and an inflammatory response.
Apoptosis is PCD - controlled disassembly of cell contents without disruption and with no inflammatory response.
66
Describe necrosis.
Plasma membrane becomes permeable, e.g. trauma. Cell swelling and rupture of cellular membranes releases proteases leading to autodigestion and dissolution of the cell.
Localised inflammation.
67
Describe apoptosis.
Latent phase: death pathways are activated, but cells appear morphologically the same.
Execution phase: loss of microvilli and intercellular junctions, cell shrinkage, loss of plasma membrane and asymmetry, formation of membrane blebs.
Fragmentation into membrane-enclosed apoptotic bodies.
Plasma membrane remains intact: no inflammation
Apoptotic bodies are phagocytosed by neighbouring cells and roving macrophages.
68
Describe the role of cysteine-dependent aspartate-directed proteases (caspases) in apoptosis.
Caspases divided into initiator and effector caspases. Form homotypic protein-protein interactions be activate each other.
Initiator caspases cleave and activate effector caspases, which carry out apoptosis. Effector caspases cleave and inactivate proteins or complexes and activate enzymes.
69
Describe the extrinsic ("death by design") pathway of caspase activation in apoptosis.
Death receptors, e.g. Fas, present on cell surface. Ligand binds to receptors - cause TRIMERISATION. Adapter protein FADD binds to cytoplasmic domain of Fas via death domain (DD).
Procaspase 8 binds to each FADD via death effector domain (DED) - forming the death-inducing signalling complex (DISC). This oligomerisation of procaspase 8 leads to activation to caspase 8, which in turn activates caspase 3 (an effector caspase).
70
Describe the role of FLIP as a cytoprotective molecule.
FLIP competes with procaspase 8 for the DED domain of FADD. If prevents transcleavage of procaspase 8, preventing activation.
71
Describe the intrinsic ("death by default") pathway of caspase activation in apoptosis.
Cellular stresses lead to loss of mitochondrial membrane potential. Cytochrome C released.
Apoptotic activating factor-1 (Apaf-1) forms a heptamer. Cytochrome C can bind to each of the WD-40 domains of Apaf-1. Caspase recruitment domain (CARD) recruits and oligomerises procaspase 9 - cleaves and activated and released as caspase 9 - this is the APOPTOSOME.
72
How are the extrinsic and intrinsic apoptotic pathways linked?
Caspase 8 cleaves Bid, which enhances release of mitochondrial proteins, thus augmenting apoptosome formation.
73
Which members of the Bcl-2 family are pro- and anti-apoptotic?
Bcl-2 and Bcl-xL are anti-apoptotic. They bind to Bax and Bak (pro-apoptotic) on the mitochondrial membrane, preventing them from forming pores.
Bad (pro-apoptotic) binds to Bcl-2 to displace it from Bax and Bak.
Bid is also proapoptotic.
PKB/Akt phosphorylates Bad, inactivating it to preventing it from binding to Bcl-2.
74
What are inhibitors of apoptosis proteins (IAPs)?
Proteins which regulate the extrinsic pathway of PCD. They bind to procaspases to prevent activation and also bind to caspases to inhibit their activity.
75
Give cytoprotective molecule examples.
Intrinsic pathway: Bcl-2, Bcl-xL
Extrinsic pathway: IAPs, FLIP
Growth factor pathways via PI3'K and PKB/Akt.
76
Give the steps of angiogenesis.
Tip/stalk selection
Tip cell navigation, stalk cell proliferation.
Branching coordination.
Stalk elongation, tip cell fusion, lumen formation.
Perfusion and vessel maturation.
77
Describe how hypoxia is a trigger of angiogenesis.
Hypoxia-inducible transcription factor (HIF) controls regulation of gene expression by oxygen, including vascular endothelial growth factor (VEGF).
78
Describe the role of VEGF in sprouting angiogenesis.
In sprouting angiogenesis, specialised endothelial tip cells lead the outgrowth of blood-vessel sprouts towards gradients of VEGF.
In stable vessels, Dll4 (a transmembrane protein which acts as a notch receptor ligand)and Notch signalling maintain quiescence. VEGF activates expression of Dll4, which drives notch signalling. Notch signalling inhibits expression of VEGFR2 in the adjacent cell.
As such, the Dll4-expressing tip acquires a motile, invasive phenotype.
Adjacent (stalk cells) form the base of the emerging sprout and proliferate.
79
Describe the notch pathway.
Notch receptors and ligands (Dll4) are membrane bound proteins that associated through their extracellular domains. The intracellular domain of notch (NICD) translocates to the nucleus and binds to a transcription factor (RBP-J) to maintain quiescence.
80
Briefly describe the role of macrophages in angiogenesis.
They carve out tunnels in the ECM, providing avenues for capillary infiltration.
81
Describe angiopoietin 1 and 2.
Angiopoietin 1 binding to tie2 receptors promotes vessel stability and inhibits inflammatory gene expression.
Angiopoietin 2 antagonises ang-1 signalling, promoting vascular instability and VEGF dependent angiogenesis.
82
Which diseases may lead to a rise in angiopoietin 2 levels?
Congestive heart failure
Sepsis
CKD (chronic kidney disease)
83
What is the angiogenic switch?
A tumour less than 1 cubic mm in volume can rely on diffusion from host vasculature for O2 and nutrients.
Larger tumours require new vessel network; the angiogenic switch is a discrete step in tumour development at which point the tumour requires vascularisation for continued growth.
84
Describe tumour blood vessels.
Irregularly shaped, dilated, tortuous.
Not organised definitively (into venules, arterioles and capillaries).
Leaky and haemorrhagic, partly due to overproduction of VEGF.
Perivascular cells (pericytes) loosely associated.
((Cancer associated fibroblasts (CAFs) secrete ECM and proangiogenic GFs (e.g. VEGF). Leaky vessels enhanced by angiopoietin 2)).
85
How does soluble VEGF-R affect angiogenesis?
It binds to VEGF and sequesters it, preventing angiogenesis.
86
What is avastin? How many resistance to it arise?
An anti-VEGF humanised Mab.
It has many side effects and limited efficacy. It has, however, been shown to be useful for age-related vascular degeneration.
Resistance due to VEGF inhibition aggravating hypoxia increasing the tumour's production of other angiogenic factors, tumour vessel lining being less sensitive and pericyte recruited in tumours being less sensitive to VEGF.
87
What is tumour cell vasculogenic mimicry (VM), also known as vascular mimicry?
Describes plasticity of aggressive cancer cells forming de novo vascular networks. The tumour cells themselves create channels for blood flow.
88
Why is sustained and aggressive antiangiogenic therapy falling out of favour?
It damages healthy vasculature, leads to loss of vessels, creates vasculature resistance to further treatment and inadequate delivery for oxygen and drugs.
Aim is to balance angiogenesis to normalise growth, reducing hypoxia and increasing efficacy of conventional therapies.
89
Briefly describe how a benign tumour becomes malignant.
The metastatic cells become de-differentiated, lose their adhesion to other neighbouring cells and lose their polarity.
They become mobile mesenchyme-like cells and enter the blood stream.
Extravasation and subsequent reformation of the tumour cell type results in a secondary tumour.
90
What are the types of tumour migration?
Individual tumour cell migration: amoeboid and mesenchymal migration (mesenchymal can be chains or single cells).
Amoeboid has low levels of integrin and cadherin.
Mesenchymal has some integrins, and chains have some cadherins.
Collective tumour cell migration: clusters and multicellular strands/ sheets.
These have high levels of cadherins and integrins.
91
What are filopodia and lamellipodia?
Filopodia are finger-like protrusions rich actin.
| Lamellipodia are sheet-like protrusions rich in actin.
92
Explain the process of cell motility.
Overview: extension, adhesion, translocation, de-adhesion.
The lamellipodium extends forward by actin polymerisation and forms a new focal adhesion.
This puts the cortex under tension, so the intracellular components move forward to relieve the tension. The retraction of the opposite pole of the cell restores normal structure.
93
What type of stimuli cause cell motility?
Chemotactic movement = chemoattractants
| Hapoptatic movement = in response to mechanical/ physical stimuli.
94
Describe how actin is found in the cell.
Found a G (globular) type (small, soluble monomers) and F (filamentous) type (large polymers).
In the cortex of the cell, found as a gel-like network.
Found as stress fibres as contractile bundles.
In filopodium, tight parallel bundles in one direction.
The process of cell movement depends on the disassembly of existing F actin and repolarisation to the direction of the stimulus and then subsequent polymerisation at that site.
95
Describe actin nucleation.
Arp2 and Arp3 combine with other proteins to form the ARP complex. G-actin form trimers and attach themselves to this complex.
96
What proteins facilitate or inhibit actin polymerisation?
Profilin facilitates polymerisation
Thymosin binds to free actin to prevent it.
ADF/Cofilin hydrolyse polymers.
97
What is actin capping?
Capping proteins attach at one end (-ve end = ARP complex, tropomodulin, +ve end = CapZ, gelsolin), which lowers rate of growth since the polymer can only grow at the uncapped end.
98
What is gel-sol transition?
The process of changing actin from a rigid gel structure to a soluble one which is allows flowing.
Faster in severing populations, slower in unsevered populations.
99
What is anchorage dependence?
The requirement of cells to be attached to ECM to grow and proliferate. It is an active process.
100
Describe how integrins are switched "off" and "on".
They have a "head" region and a "leg" region, which spans the plasma membrane. They can adopt flexed or extended conformations: at flexed conformation, there is weak or no binding of the ligand. At extension, there is strong association.
101
Describe "outside-in" cell signalling.
20 combinations of A and B integrin heterodimers. Bind to short sequences on ECM proteins, often found in more than one protein. The composition of the ECM determines which integrin complexes bind and which signal the cell receives (there is mechanical continuity between cytoskeleton and ECM via integrins). This can alter the phenotype.
102
What is the new theory to explain apparent contact inhibition of cell division, where cells which form a confluent monolater cease proliferating and slow their metabolism.
Density-dependence of cell division - the fact that competition for external factors (e.g. growth factors) is responsible for the reduced proliferation, not cell-to-cell contact.
103
Why is growth factor (density-dependence) and ECM binding (anchorage dependence) required for cellular proliferation?
Since GFs and integrin signalling complexes both activate the MAPK pathway.
Individually, this is weak/transient.
Together, activation is strong and sustained. These separate signalling pathways act synergistically.
104
Describe contact inhibition of locomotion.
When most non-epithelial cells "collide", they don't form stable cell-to-cell contacts but "repel" one another by paralysing motility at the contact site and promoting formation of a motile site at another site on the cell.
105
How does cell-cell adhesion reduce proliferation?
B-catenin binds to cadherin intercellular junctions. Unable to bind to LEF1, a transcription factor which transcribes proteins involved in cellular proliferation.
Also, some transcription factors associated with cell junctions, reducing capacity to promote proliferation.
Cadherin clustering alters GTPases, Rac activated.
106
How does a mutation in adenomatous polyposis coli (APC) complex lead to cancer?
When B-catenin isn't bound (no cell-to-cell junctions) it is rapidly broken down by APC complex.
If it is inactive, free B-catenin increases. Leads to cell proliferation by activating LEF1 TF.
107
How do changes in cell motility lead to cancer?
Loss of behaviour restraints: proliferate uncontrollably (lose density dependence), less adherent (lose anchorage dependence), multilayer (lose inhibition of locomotion).
For a primary tumour to metastasise, cell-cell adhesion must be downregulated (cadherin reduced), and cells must be motile.
Degradation of ECM must occur: matrix metalloprotease (MMP) increases.
N.B. degree of carcinoma cell-cell adhesion is an indicator of how differentiated the primary tumour is and indicates its invasiveness and prognosis.
108
What are proto-oncogenes?
Genes that code for essential proteins involved in maintenance of cell growth, division and differentiation.
109
What is an oncogene?
A proto-oncogene which has mutated to form a protein product which no longer responds to control influences
110
How do protooncogenes mutate to form oncogenes?
```
Can be a single mutation. Results include an aberrantly active protein, an aberrantly expressed or over-expressed protein.
Chimeric genes (genes formed by combinations of portions of one or more coding sequences to produce new genes, a problem if one of the pieces of translocated DNA is a gene promoter or if the fusion gene forms an abnormal protein).
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111
How can Ras become an oncogene?
Mutant Ras fails to dephosphorylate GTP and remains constitutively active.
This is an example of how mutations can lead to downstream activation of signalling pathways such that they no longer respond to upstream stimuli.
112
What are tumour suppressor genes?
Typically proteins whose function is to regulate cellular proliferation and maintain cell integrity.
Each cell has 2 copies of each tumour suppressor gene.
Mutation or deletion of just one gene is usually insufficient to promote cancer.
113
Describe Knudson's 2-hit hypothesis.
For mutation of tumour suppressor genes to cause cancer sporadically, you need to acquire 2 mutations.
In hereditary cancer, one allele may be mutated already, so only one mutation needs to be acquired.
Leads to early onset cancers, cancers in bilateral organs, and synchronous and successive tumours in affected individuals.
114
What is important about the susceptibility of the tumour suppressor gene p53 to mutations?
Mutations act in a dominant manner, so mutation of a single copy is sufficient for dysregulation of activity.
115
Describe the pathway for the development of colorectal cancer.
Adenomatous polyposis coli (APC) is a tumour suppressor, which binds to B-catenin, rapidly degrading it, preventing it from binding to the transcription factor LEF1 (whose activation leads to cell proliferation). This leads to hyperproliferation of the epithelium: benign adenomatous polyps.
DNA hypomethylation (epigenetic) combined with a Ras (oncogene) mutation will make the polyps develop into adenomas.
The mutation of p53 will result in the development of carcinoma.
116
Contrast oncogenes and tumour suppressors.
Oncogenes active in tumours; tumour suppressors inactive.
Oncogenes arise from translocations/ point mutations; tumour suppressors from deletions or mutations.
Oncogenes are rarely inherited, tumour suppressor mutations can be inherited.
Oncogenes dominant at cell level; TSGs are recessive.
Oncogenes has broad tissue specificity; tumour suppressors have considerable specificity.
117
How do migrant studies help identify carcinogenic factors?
Extent and role of change are informative.
A rapid change in risk following migration implies that lifestyle/environmental factors act late in carcinogenesis.
A slow change suggests that exposures early in life are most relevant.
Persistence of rates between generations suggests genetic susceptibility is important in determining risk.
118
In HIGH income countries, describe the changes in incidence and mortality of cancer which have been seen over the last few decades.
Incidence has increased, but is not starting to plateau.
| Despite the increases in incidence, mortality has decreased in recent decades.
119
What is meant by "westernisation" of lifestyle?
Energy-dense diet, rich in fat, refined carbs and animal protein.
Low physical activity.
Smoking and drinking.
120
When are mammograms used and what do we look for?
Breast screening: all women aged 50-64 (being extended to age 70) are invited for screening.
Asked to attend every 3 years in this range -> 70% of women attend these.
If a woman does have breast cancer and it has been treated successfully, surveillance mammograms are conducted annually for at least 5 years to make sure it hasn't returned.
One looks for calcification.
121
In staging of breast cancer, what distinguishes T1, 2 and 3?
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T1 = tumour less than 2cm across.
T2 = tumour 2-5cm across
T3 = tumour >5cm across.
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122
Describe the role of oestrogen in normal breast and breast cancer.
Oestrogen binds to the oestrogen receptor (ER) which binds to specific DNA sequences called oestrogen response elements to promote gene expression. The products, e.g. progesterone receptors, cyclin D1, c-Myc, TGF-A, which increase cell proliferation. ER overexpressed in 70% of breast cancers - resulting in breast cancer.
123
Describe how oestrogen withdrawal is useful in breast cancer.
Results in responses in 70% of ER+ breast cancer, and 5-10% of ER- breast cancer.
ER+ cancers have good prognosis in women, poor prognosis in men.
Paradoxically, post-menopausal breast cancers can respond to high-dose therapy with oestrogen analogues (down-regulates ER via negative feedback).
124
Describe how ovarian ablation can be useful in the treatment of pre-menopausal ER+ breast cancers.
The ovaries are the major source of oestrogen biosynthesis in pre-menopausal women. Surgical oophorectomy or ovarian irradiation successful in 1/3 of pre-menopausal breast cancers.
However, morbidity and irreversibility are issues with this treatment.
125
Describe the role of medical ovarian ablation (endocrine therapy).
Reversible and reliable.
Use GnRH agonists, bind to GnRH receptors in the adenohypophysis which leads to receptor downregulation and suppression (negative feedback) - which inhibits ovarian function (which includes oestrogen production).
126
Other than medical ovarian ablation, what other types of endocrine therapy are available for treatment in ER+ breast cancers?
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Aromatase inhibitors (prevent peripheral conversion of androgens to oestrogens).
Antioestrogens binds to the ER without gene expression. High efficacy, few side effects (most common is hot flush).
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127
What class of drugs does tamoxifen belong to, and why are they particularly useful?
Belong to selective oestrogen receptor modulators (SERMs).
Tamoxifen acts as an antioestrogen in the breast (desired).
In bone, where oestrogen is important in maintenance, tamoxifen is pro-oestrogenic.
In the CVS, where oestrogen lowers LDL and raises HDL, tamoxifen is also pro-oestrogenic.
However, it raises the risk of thromboembolisms and is pro-oestrogenic in the uterus, promoting endometrial cancer.
It also promotes cataracts.
128
Why are aromatase inhibitors particularly useful in post-menopausal women?
The major source of oestrogen in post-menopausal women is conversion of adrenal hormones to oestrone (E2). Conversion occurs at extra-adrenal sites, such as fat (hence obesity is a risk factor for breast cancer), liver and muscle.
Type I = irreversible
Type II = reversible
129
What factors increase lifetime oestrogen exposure?
Obesity (fat is a site of oestrogen production)
Early menarche (first menstrual cycle)
Late onset of menopause
Use of contraceptives containing oestrogen.
Late first full-term pregnancy (or no pregnancies)
Use of hormone replacement therapies containing oestrogen.
130
What is the principal treatment for ER- breast cancers?
Chemotherapy (6 months).
131
Define polyp
Any projection from a mucosal surface into a hollow viscus (viscus = singular of viscera) and may be hyperplastic, neoplastic, inflammatory, hamartomatous etc.
132
In colon cancer, what is an adeoma?
A benign neoplasm of the mucosal epithelium cells - a type of polyp.
133
Describe hyperplastic polyps.
Very common, <0.5cm, 90% of all large intestine, often multiple with NO malignant potential (non-cancerous, non-adenomas).
134
Describe adenomatous polyps.
Tubular, villous or tubulovillous
Tubular - columnar cells with nuclear enlargement, elongation, multilayering and loss of polarity. Increased proliferative activity, reduced differentiation, complex and disorganised.
Villous - mucinous cells - same features. Exophytic, frond-like extensions, rarely hypersecretory.
135
Describe the epidemiology of colorectal carcinomas (CRCs)
25% of adults have adenomas at age 50. 5% of these become cancers if left. Lead time around 10 years.
Cancers may stay at curable stage for around 2 years.
Most CRCs arise from adenomas, residual adenoma in 10-30% of CRCs.
Endoscopic removal of polyps decreases the incidence of subsequent CRC.
136
Summarise the genetic predisposition to colon cancer.
HNPCC (hereditary non-polyposis colorectal cancer) - microsatellite instability. Repeat sequences prone to misalignment, which can be in coding sequences of genes which inhibit growth or apoptosis.
FAP - inactivation of APC tumour suppressor genes.
137
How does diet affect colon cancer risk?
High fat, low fibre, high red meat, refined carbohydrates increase risk. Food contains both carcinogens and anti-cancer agents though!
Heterocyclic amines (HCAs) found in meat cooked at high temperatures are mutagenic.
Folates are co-enzymes for nucleotide synthesis and DNA methylation. Deficiency leads to disruption in DNA synthesis leading to DNA instability.
Vitamins C & E are ROS scavengers - anti-cancer.
138
How do colon cancer patients present?
Change in bowel habit, bleeding via rectum, unexplained iron deficiency anaemia, mucous in faeces, bloating, cramps, weight loss, fatigue.
N.B. patients and doctors rationalise these symptoms as getting old.
139
Where are colon cancers most commonly found?
Rectosigmoid colon = 55%
Ascending colon/ caecum = 22%
Transverse colon = 11%
Descending = 6%
140
How is colon cancer treated at its different stages?
Stage I = surgery
Stage II = surgery + 5-FU (chemo)
Stage III = surgery + multiple chemotherapy
Stage IV = surgery + metastasectomy + chemo +/- palliative care.
141
Who do we screen for colon cancer?
NHS screening: FOB/FIT kit. Positives referred: 60-75 = colonoscopy, 55-60 = sigmoidoscopy.
Screen high-risk individuals: previous adenoma, FHx, uterine carcinomas, ulcerative colitis and Crohn's disease.
142
What is the order to adenoma carcinoma sequence?
APC, K-ras, p53, telomerase activation.
143
Define leukaemia.
Mutations in a single lymphoid or myeloid stem cell leads to abnormalities in proliferation, differentiation or cell survival leading to steady expansion of the leukemic clone. N.B. abnormal cells not always present in the blood (a bone marrow disease), and leukaemia means "white blood".
144
Describe Duke's classification for colon cancer.
Dukes A = growth limited to mucosa/ submucosa.
Dukes B1 = growth into muscularis propria, but not penetrating through it
Dukes B2 = growth penetrating through muscularis propria.
Dukes C1 = growth into muscularis propria, not penetrating through it, NODES involved.
Dukes C2 = growth penetrating through muscularis propria - nodes involved.
Dukes D = distant metastatic spread.
145
How it leukaemia a unique type of cancer.
Most cancers are solid tumours - uncommon for leukaemia to have tumours (the cells circulate in the blood, with haematopoietic stem cells and their derivatives being able to enter tissues. The concepts of invasion and metastasis can't be applied. Leukaemias which behave in a relatively "benign" manner are chronic, whereas those behaving in a relatively "malignant" manner are ACUTE - very aggressive, with swift patient death if untreated.
146
What types of leukaemia are there?
Depends on cell of origin - can be myeloid or lymphoid, which can itself be of B or T cell lineage.
Acute lymphoBLASTIC leukaemia (ALL), acute myeloid leukaemia (AML), chronic lymphoCYTIC leukaemia (CLL), chronic myeloid leukaemia (CML).
147
Is leukaemia preventable? (Philosophy).
Leukaemia is an acquired genetic disease resulting from somatic mutation. The fact that it is caused by random events rather than exogenous influence means that leukaemia may be a result of the nature of the human genome: an inevitable part of the ability of mankind to change through evolution.
Obviously, things like Down's syndrome, chromosomal fragility syndromes, irradiation, chemotherapy, cigarettes and chemicals like benzene increase chromosomal breaks - increasing risk.
148
Describe acute lymphoblastic leukaemia (ALL)
Increase in lymphoblasts (failure to mature into T and B cells).
Largely a disease of children.
Crowding out of normal cells leads to fatigue, lethargy, pallor, breathlessness (anaemia), fever and other features of infection (neutropenia), bruising, petechiae, bleeding (thrombocytopenia).
Anaemia (normocytic, normochromic), leukocytosis, neutropenia, replacement of bone marrow by lymphoblasts, thrombocytopenia.
149
Describe acute myeloid leukaemia (AML)
Cells continue to proliferate but no longer mature. Build up of myeloblasts or "blast cells" in bone marrow which spread into the blood. Failure of normal function
(failure of production of end cells).
Hemorrhage and swelling (infiltration) of gums
150
Describe chronic myeloid leukaemia (CML)
Mutations affect genes encoding proteins in signalling pathway between a cell surface receptor and the nucleus. Cell kinetics and function not as seriously affected. However, the cell becomes independent of external signals (apoptosis) leading to increased production.
151
Describe chronic lymphocytic leukaemia (CLL)
The leukaemic cells are mature B or T cells, but abnormal.
152
What are the signs and symptoms of leukaemia?
Accumulation of abnormal cells leads to leukocytosis, bone pain (if acute), hepatomegaly, splenomegaly, lymphadenopathy (if lymphoid), thymic enlargement (if T-cells), skin infiltration, testicular enlargement.
Metabolic effects = hyperuricemia, renal failure, weight loss, low grade fever, sweating, anaemia, neutropenia, thrombocytopenia.
153
What social influences affect leukaemia risk?
Early exposure to pathogens protects against leukaemia. Evidence relates to family size, new towns, socio-economic class.
154
How can we detect which type of leukaemia a patient has?
Difficult to tell if lymphoblast or myeloblast. Cytogenetic analysis useful for management as it informs prognosis.
Hyperdiploidy = good prognosis. Translocation (fusion gene) = poor prognosis. Translocations can be detected by fluorescent probes: fusion leads to a mix of colours.
155
How is acute lymphoblastic leukaemia (ALL) treated?
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Supportive therapy (red cells, platelets, antibiotics).
Systemic and intrathecal chemotherapy (need to kill abnormal cells in CNS otherwise residual CNS cells will cause relapse after remission). Alternatively, give high dose systemic chemo which can cross BBB.
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156
The vast majority of skin cancers are derived from the epidermis. Briefly, give the basic structure of the epidermis, from superficial to deep.
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Stratum corneum = dead keratinocytes
Stratum lucidum
Stratum granulosum
Stratum spinosum (living keratinocytes)
Stratum basale (dividing keratinocytes, stem cells and melanocytes).
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157
What type of skin cancers are there?
Keratinocyte derived e.g. basal cell carcinoma, squamous cell carcinoma (aka non-melanoma skin cancers (NMSCs)).
Melanocyte derived e.g. malignant melanoma.
Vasculature derived e.g. Kaposi's sarcoma, angiosarcoma.
Lymphocyte derived e.g. mycosis fungoides.
BCC and malignant melanoma incidence increasing, but only in white people.
158
What can cause skin cancer?
Genetic syndromes, viral infections (HPV in SCC), UV light (BCC, SCC, malignant melanoma), immunosuppression (Drugs, age, HIV).
159
Describe how UV light can cause skin cancer.
UVB (280-310nm) most important for causing skin cancer.
UVA (310-400nm) contributes to skin carcinogenesis and is a major cause of skin ageing. 100x more UVA penetrates to Earth's surface than UVB.
UVB - directly introduces abnormalities (photoproducts - pyrimidine dimers T=T, C=C, T=C). Usually repaired quickly by nucleotide excision repair.
UVA induces pyrimidine dimers less efficiently than UVB. Free radicals damage DNA and cell membrane.
If UV causes damage leads to DNA damage in gene controlling cell division, DNA repair or cell-cycle arrest, can lead to UV-induced skin carcinogenesis.
160
Describe xeroderma pigmentosum.
A genetic condition with defective nucleotide excision repair, meaning UV-induced photoproudcts aren't repaired,
161
Describe sunburn.
UV leads to keratinocyte cell apoptosis. Sun burn cells are apoptotic cells in UV overexposed skin. Apoptosis removes UV damaged cells in the skin which might otherwise become cancer cells.
162
Describe how UV light is involved in immunomodulation.
UVA and UVB affect the expression of genes involved in skin immunity - deplete Langerhans cells in the epidermis.
Leads to reduced skin immunocompetence and immunosurveillance (basis for UVA phototherapy for, e.g. psoriasis). This further increases the cancer causing ability of sun exposure.
163
Host responses to UV light determined by skin phototype (genetic influence). Describe the Fitzpatrick phototypes.
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I = always burns, never tans
II = usually burns, sometimes tans
III = sometimes burns, usually tans
IV = never burns, always tans
V = moderate constitutive pigmentation (Asian)
VI = marked constitutive pigmentation (Afro Caribbean)
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164
Describe melanin.
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Pigment responsible for skin colour. Produced by melanocytes within basal layer of epidermis - colour depends on amount produced not density of melanocytes.
2 types: eumelanin (brown or black) and pheomelanin (yellowish or reddish brown).
MCR1 gene (>20 polymorphisms) leads to variation in eumelanin and is responsible for different hair and skin colours.
In response to UV exposure, keratinocytes release MSH (paracrine signalling) which increases melanocyte production by melanocytes. Melanin taken into melanosomes which are mobilised to surround the nucleus to protect from UV light.
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165
Describe malignant melanoma
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Melanocytes abnormal (atypical cells and architecture) - caused by UV exposure and genetic factors.
Superficial spreading = lateral proliferation, invading basement membrane.
Nodular = vertical proliferation (moles).
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166
Describe lentigo maligna
Melanoma in situ - proliferation of malignant melanocytes within the epidermis - growth along the stratum basale - no risk of metastasis.
Irregular shape, light and dark brown colours. Usually >2cm.
If it invades - becomes lentigo maligna melanoma.
167
How are melanomas diagnosed?
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ABCD rule:
asymmetry
border irregular
colour variation (dark brown - black)
diameter >0.7cm
(erythema)
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168
What are the types of malignant melanoma?
Superficial spreading, nodular, lentigo maligna melanoma, acral lentiginous (common on soles of feet), amelanotic (apigmented).
169
How is the prognosis of melanoma determined?
Breslow thickness: measurement from granular layer to bottom of tumour.
170
What are the risk factors for malginant melanoma?
FHx, UV, sunburns in childhood, personal history of melanoma, atypical/dysplastic nevi, skin types I/II.
171
Describe squamous cell carcinoma (SCC) (a NMSC).
A malignant tumour of keratinocytes, caused by UV exposure, HPV, immunosuppression. Risk of metastasis.
Well differentiated = keratin horn.
Poorly differentiated = no horn.
172
Describe basal cell carcinoma (BCC) (a NMSC)
Malignant tumours arising from basal layer of epidermis. Caused by sun exposure and genetics. Slow growing (3-4mm per year), invades tissue but DOES NOT metastasise.
Common on face.
Can be nodular or superficial.
173
Describe mycosis fungiodes
A cutaneous t-cell lymphoma. Slowly progressing. Pink scaly plaques.
174
What are the symptoms of prostate hyperplasia (whether benign or malignant)?
Problems with urination (due to the prostate surrounding the urethra).
More rarely, the patient may suffer from lower back pain or blood in the urine.
Tumours may spread to seminal vesicles/ bladder or metastasise to bone: the major symptom of metastatic disease is bone pain.
175
How is PSA used to detect prostate cancer?
The prostate is an exocrine gland and PSA is a normal component of seminal fluid. Normally, epithelial gap junctions, the basal cell layer and basement membrane prevent PSA entering the tissue and blood serum, so PSA levels in the blood serum of men with no prostate disease is usually undetectable. Any damage to the prostate allows PSA to escape into the serum: 4ng/ml is taken to indicate the possibility of prostatic disease.
Raised PSA may be due to benign or malignant disease, as well as mechanical damage (e.g. bike riding), urinary tract infections and prostatitis. Hence, further tests are required to determine the cause.
176
Explain the Gleason scoring system of prostate cancer.
Two largest areas of tumour (From biopsies) are scored 1-5 (1 is least aggressive, 5 = most) and the two scores are quotes, plus their sum (e.g. 3+4,7).
2-4 = low grade, 5-7 = intermediate, 8-10 = high grade.
177
What is the argument against routine PSA screening in men?
Once a raised PSA is detected, the man will have to have further, invasive tests as well as a period of acute anxiety. If malignancy is detected, he will undergo treatment with unpleasant side effects, which will reduce quality of life dramatically. Meanwhile, it is probable that the lesion, if left alone, wouldn't have been problematic in his lifetime.
178
When would "watchful waiting" or "active observation" be the favoured "treatment" for prostate cancer?
In older patients with low-grade tumours.
179
What are the criteria for radical prostatectomy?
Tumour confined to the gland
PSA < 10-12 ng/ml
Age <70
180
Describe the hormonal treatment of prostate cancer.
Leuprorelin - a GnRH (LHRH) agonist. Overstimulates pituitary GnRH-R, causing them to be desensitised so that they no longer respond to LHRH. Hence, LH production ceases and testosterone production by testes drops.
Flutamide - an androgen receptor antagonist - given to block the effects of weak-adrenal androgens and residual testicular testosterone.
181
What are some of the side effects of hormonal therapy of prostate cancer?
Osteoporosis, loss of libido, anaemia, muscle atrophy, memory loss, gynaecomastia.
182
By what mechanisms can prostate cancer advance to
| "androgen independence"?
Amplification of the response of androgen receptor to low residual levels of androgens, or weak androgens.
Decreased levels of co-repressors
Mutation of the androgen receptor causing it to become activated by other ligands (e.g. oestrogen).
Amplification/ over-expression of androgen receptor
Androgen receptor pathway bypassed (e.g. loss of PTEN). PTEN antagonises androgen signalling.
Change in intracellular transduction pathway so it works better.
183
What is the principle progestin used in breast cancer therapy and why are progestins useful?
The progestin response in breast is complex but has effects on proliferation and differentiation. They have shown to be anti-neoplastic.
Poor absorption has been overcome with synthetic derivative progestins. The principal progestin is megestrol acetate.
