Week 2 - Cancer Flashcards
What is meant by metastasis?
Tumours spreading to different sites.
What is malignant tumour?
A tumour that will spread.
Define a carcinoma.
A malignant tumour derived from epithelial cells.
Define a sarcoma.
Malignant tumour derived from mesenchymal cells.
Define a melanoma.
Malignant tumour derived from neural crest cells.
Define leukaemia.
Malignant tumour derived from circulating white blood cells.
Define a lymphoma.
Malignant tumour derived from the lymphatic system.
What is the most common classification of malignant tumours?
Caricnoma
What is the function of the basement membrane?
It delineates epithelial or endothelial tissues.
What is the basement membrane secreted by?
The cells that lie next to it:
Basal keratinocytes or endothelial cells.
Which collagen type is specific to basement membrane?
Type IV collagen
What is meant by a carcinoma in situ?
The cells are histologically malignant but still trapped in the basement membrane.
After which size will a tumour need its own blood supply?
> 1mm
What is meant by intravasation?
The process of getting into the circulation .
What is meant by extravasation?
The process of getting out of circulation.
Which 4 steps in the metastatic cascade are common to invasion and metastasis?
Reduced cell-cell adhesion
Altered cell-substratum adhesion
Increased motility
Increased proteolytic ability.
Which steps in the metastatic cascade only involve metastasis?
Angiogenic ability
Ability to intravasate and extravaste.
Ability to proliferate (locally and in ectopic sites).
What type of junction is found between cells?
Adherans junctions.
What does beta cadherin bind to?
Alpha cadherin
What is meant by homotypic adhesion?
The ligand and receptor are the same molecule.
Give an example of homotypic adhesion.
E cadherin in adjacent cells.
What are E-cadherins bound to within the cell?
Catenins
Where is E cadherin expressed?
On the cell surface of all epithelial cells.
What is the structure of catenins on the inside of the cell?
B-catenin binds on one side to E-cadherin and on the other side to a-catenin. A-catenin binds on its other side to the actin-myosin cytoskeleton
What is required in the extra cellular space for E-cadherin adhesion?
Calcium
What does loss of E-cadherin lead to?
Epithelial mesenchyme transition
What is the correlation between E-cadherin expression and tumour grade?
Negative correlation.
In which ways might a tumour disregulate E-cadherin function?
Exon-skipping
Promotor turned off
Mutation in regulators of expression
What is meant by exon-skipping?
E-cadherin is mutated and loses two exons which code for the calcium binding domain. If calcium cannot bind, the E-cadherin molecule doesn’t work.
Name 3 mutations in transcription factors that regulate E-cadherin.
Snail
Slug
Twist
Which proteins are important in cell adhesion to the substratum?
Integrins
What do integrins bind to?
ECM molecules
What is the structure of integrins?
Heterodimeric: alpha and beta chain.
Give an example of a molecule an integrin might bind to.
a5b1 - fibronectin receptor.
Which specific integrin seems to promot invasion?
Vitronectin receptor (integrin avB3).
What are the possible mechanisms by which integrins can promote metastasis?
Decrease adhesion to basement membrane surrounding epithelium.
Increase migration through stroma.
Increase adhesion to basement membrane or endothelial cells of blood vesse’s binding site for proteolytic enzymes.
What can induce epithelial cells to dissociate?
HGF/Scatter factor.
What is HGF?
A mitogen (growth factor), a motogen (motility factor) and a morphogen.
What produces HGF?
Stromal cells in the tumour microenvironment.
What happens when HGF binds to c-met?
Increased tyrosine phosphorylation of B-catenin in tumour epithelial cells, which leads to disrupted E-cadherin mediated adhesion.
Give some example of a tumour-stroma interaction.
c-met/HGF Chemokine receptor/chemokine Protease receptor/protease Integrin aB2/MMP-2 TGF/Stromelysin VEGF/VEGFR
Which cells are in the tumour microenvironment?
Cancer-associated fibroblasts Immune cells that have infiltrated the tumour Myofibroblasts Tumour-associated vasculature Pericytes
What do cells in the tumour microenviornment secrete/
Growth factors
Chemokines
Enzymes
Give two classes of proteases that could be involved in metastasis.
Serine proteases
Matrix metalloproteinases.
Give an example of a serine protease.
Urokinase plasminogen activator.
Where are membrane type - matrix metalloproteinases found?
Embedded in the membrane.
What are matrix metalloproteinases produced by?
White blood cells.
What does a tumour cell express when it is hypoxic?
HIF - hypoxia inducible factor.
What is the effect of expression of HIF?
Upregulation of VEGF.
What does VEGF bind to?
Nearby endothelial cells.
What is the effect of VEGF binding to endothelial cells?
Induces them to multiply and form tubes towards the tumour. New blood vessels are leaky - fibronogen and other plasma proteins leak out. Pro-coagulants will convert fibrinogen to fibrin. The fibrin clot is a good surface for endothelial cells to migrate on.
What is the rolling and sticking model of extravasation?
WBCs slow down by weak adhesion and adhere more firmly to vessel walls. That’s a precursor to them moving into the surrounding tissue.
What is selectin important for?
Rolling and sticking
Where is selectin expresssed?
WBC surface
What was the experiement used to look at the role of selectin in mice?
A transgenic mouse has been created that only expressed L-selectin in the pancreas (rat insulin promotor has been stuck onto 5’ end of L-selectin). The same lab generated a line of mice with the rat insulin promotor controlling T-antigen (a molecule that make human cells grow out of control). When they crossed both lines of mice the progeny had metastatic disease - 2 step process.
What are the principal sites of metastasis for breast cancer?
Bone
Lungs
Liver
Brain
What are the principal sites of metastasis for lung adenocarcinoma?
Brain
Bones
Adrenal gland
Liver
What are the principal sites of metastasis for skin melanoma?
Lungs
Brain
Skin
Liver
What are the principal sites of metastasis for colorectal cancer?
Liver
Lungs
What are the principal sites of metastasis for pancreatic cancer?
Liver
Lungs
What are the principal sites of metastasis for prostate cancer?
Bones
What are the principal sites of metastasis for sarcoma?
Lungs
What are the principal sites of metastasis for uveal melanoma?
Liver
What is the seed and soil theory?
Tumour cell is the seed but needs an appropriate microenvironment to grow.
What is the argument against seed and soil theory?
Lack of contralateral breast and kidney tumours.
What is the mechanical hypothesis?
It’s all about blood supply.
What are the arguments against the mechanical hypothesis?
Dudoenal tumour fails to seed liver metastasis.
What are the general theories as to why tumours grow in different distance sites?
Selectins
Selective response to growth factors.
Selective migration to chemokines expressed in different tumours.
Factors released by tumour cells precondition certain distant organs to be receptive when the tumour gets there.
Balance of local angiogenic factors versus systemic anti-angiogenic facotrs.
What is the first thing that identifies cancer cells as foreign?
Down regulated MHC class 1 receptors.
How does the body respond to cells with downregulated MHC class 1 receptors?
NK, NKT look for damaged cells and attack. Either directly or by releasing interferon gamma which triggers a response around the tumour.
What will interferon gamma activate?
Local macrophages and dendritic cells which will start to kill tumour cells.
What do dendritic cells initiate?
The adaptive immune response.
How does the adaptive immune system respond to cancer cells?
T cells directed against the tumours.
B cells attack.
Plasma cells start producing antibodies
How do tumour cells avoid the immune system?
Genetic heterogeneity means there are new versions of the same cells constantly being produced.
What are the three E’s of immunoediting?
Elimination
Equilibrium
Escape
What is meant by elimination in reference to immunoediting?
Default mechanism - in most cases the immune system removes the cancer before it ever becomes established.
What is meant by equilibrium in reference to immunoediting?
A state in which the immune system has no eliminated the cancer, but the cancer is not growing further. This phase can last for years or decades, until a person is immunosuppressed at which point the immune system loses the ability to suppress the cancer cells.
What is meant by escape in reference to immunoediting?
Tumour cells generate new variants of themselves all the time until they produce a type of cell that is able to avoid, evade or suppress the immune system. This is called an escape clone and is where a tumour arises from.
What are the four different approaches to immunotherapy?
Vaccination strategies.
Non-specific therapies.
Antibody therapies.
Cell-based therapies.
What was William Coley’s non-specific therapy?
William Coley found if you injected a mixture of killed bacteria into a tumour it caused a non-specific inflammatory reaction and sometimes killed the tumour.
Give an example of a current non-specific therapy.
Imiquimod (Toll-like receptor antagonist.)
IL2
What is the problem with non-specific therapies?
The immune response is very different in different patients.
What is IL2?
A T cell growth factor.
What is the problem with IL2?
You have to be a specialised IL2 physician to administer it because its therapeutic window is so narrow. It is therefore a very expensive therapy to use.