Disorders of Cell Growth Flashcards
What is a tumour
- Swelling or mass
- Two general types of tumours
- Benign (non-cancerous)
- Malignant (cancerous)
What is a neoplasm
- An abnormal mass of tissue
- Growth of which exceeds and is uncoordinated with that of normal tissues
- Persists in same excessive manner after cessation of stimuli which evoked change
What is neoplasia and dysplasia
Neoplasia:
- Cancer, new growths of cells in the body
- Mutated proto-oncogenes / tumour suppressor genes
Dysplasia:
- Irreversible
- Replacement of one mature cell type with a less mature cell type
- Mutations in genome, epigenetic changes, principally in epithelia
What are the features of a benign tumour
- Nomenclature (-oma)
- Localised
- Non-invasive, slow growth
- Resemble tissue of origin
- Encapsulated / circumscribed edge, intact surface
- Exophytic growth
- Homogenous cut surface
- No metastases
What are the features of a malignant tumour
- Nomenclature (-carcinoma or -sarcoma)
- Non-localised
- Invasive, rapid growth
- Poor resemble of tissue of origin
- Poorly defined and irregular border, ulcerated, vascular permeation
- Endophytic growth
- Heterogenous cut surface / necrosis
- Metastases common
What are the common causes of cancer
- Sporadic (non-familial) cancers caused by DNA damage and genomic instability
- Oncogenic viruses carry genes that can lead to cancer (HPV / EBV)
- Inheritance of one defective copy of a tumour suppressor gene / cancer susceptibility gene
- Li-Fraumeni Syndrome - Mutant TP53
- Hereditary Breast / Ovarian Cancer (HBOC) - Mutant BCRA1 / BRCA2
- Lynch Syndrome - Abnormal DNA mismatch repair
What are some genetic mutations found in cancer
- Gene Deletion / Inactivation: Loss-of-function, tumour suppressor genes (TP53)
- Gene Amplification: Copy number changes, hyper-activity of proto-oncogenes, oncogenes (MYC, EGFR)
- Protein Activating Mutation: Gain-of-function, BRAF V600E, IDH1 R132
- Translocations: BCR-ABL
- Epigenetic Alterations: Histone H3
What are proto-oncogenes
- Encode proteins that normally control cell growth / proliferation
- When mutated become oncogenes that cause self-sufficiency
- Extracellular signalling, hormones, GFs, signal transduction and nuclear proteins
What are oncogenes
- Jammed accelerator
- Genes / proteins that activate normal cell proliferation
- These genes are mutated in cancer resulting in uncontrolled proliferation
- Gain-of-function mutation (dominant)
- MYC, RAS, EGFR/ERBB1, HER2/ERBB2
What are tumour suppressor genes
- Defective brakes
- Genes / proteins that normally prevent cell proliferation are mutated in cancer resulting in uncontrolled proliferation
- Loss of function mutation (recessive) or loss of heterozygosity
- TP53, RB, CDKN2A (Ink4a / Arf), CDKN2B (Ink4b)
What is the p53 tumour suppressor gene (loss of function mutation)
p53 - Tetramer DNA complex containing TFs (can bind DNA), - When mutated multiple cellular processes are disrupted Activated By: - Lack of nucleotides - UV / ionising radiation - Oncogene signalling - Hypoxia - Blockage of transcription Effect: - Cell cycle arrest and senescence or return to proliferation - DNA repair - Block of angiogenesis - Apoptosis
What are gain of function mutations
- Results in constitutive kinase activity, increased stimulation
- Cause of melanoma (BRAF V600E), lung cancer, colorectal cancer, thyroid carcinoma, paediatric low grade glioma and craniopharyngioma
List the 6 hallmarks of cancer
- Sustained proliferative signalling
- Resistance to anti-growth signals
- Immortality
- Resistance to apoptosis
- Sustained angiogenesis
- Invasion / metastasis
What is sustained proliferative signalling (1)
- Constitutively activated growth signalling
- Often driven by oncogenes
What is resistance to anti-growth signals (2)
- Unregulated cell cycle progression (mutated CDKs, kinases and cyclins)
- Inactivated cell cycle checkpoints (inactivation of tumour suppressors)
- Leads to cells with aneuploidy, DNA damage and incomplete DNA replication
What is immortality (3)
- No limit to cell divisions
- Telomere length extension by telomerase, infinite replicative ability
- Inactivated cell death pathways
- Hayflick Limit: Number of times cell can divide before telomeres shorten and inhibit duplication
What is resistance to apoptosis (4)
- Resistance to programmed cell death
- Activation of survival signalling pathways (AKT)
- BCL2 over-expression in cancer prevents induction of apoptosis
What is sustained angiogenesis (5)
- Formation of blood vessels
- Activated vascular endothelial GF signalling
- Tumour: Transformed or neoplastic cells, proliferating
- Stroma: Normal cells (normal DNA), connective tissue, BV and host immune/inflammatory cells, provides support to enable tumour growth
What is invasion / metastasis (6)
- Loss of cell-to-cell interactions
- Loss of contact inhibition
- Loss of anchorage dependence
- Cells in culture and in vivo exhibit contact-inhibition
- Cancer cells lack contact inhibition feedback mechanisms, clumps or foci develop
Describe how molecular understanding of cancer can be used in research
Discovery:
- Elucidation of oncogenic mechanisms
- Identification of therapeutic targets
- Identification of cancer biomarkers
Validation:
- Validation of candidate therapeutic targets and biomarker signatures
Clinical Utility:
- Classification of patients based on disease prognosis
- Stratification of patients based on predicted therapeutic response
What is multistep carcinogenesis
- Carcinogenesis is a multistep process resulting from accumulation of multiple genetic alterations
- Collectively give rise to transformed phenotype and associated hallmarks
- Most cancers have at least 6-9 different mutations
What are common translocations / genetic changes in cancer
Translocations:
- Burkitt’s Lymphoma: Affects antibody rearrangement (T cells)
- Acute Promyelocytic Leukaemia (APL): Stalls myeloid differentiation
- Acute Lymphoblastic Leukaemia (ALL): Constitutive ABL kinase activity
- Ewing’s Sarcoma: Inhibits differentiation, solid tumour
- Deletions: Loss of tumour suppressor genes
- microRNAs (miRNA): Increase expression of oncogenes, decrease expression of tumour suppressor genes
- Epigenetic Changes: Post-translational modification of histones, abnormal DNA methylation
What is grading and staging of cancers
- Staging: Progression or spread through the body
- Grading: Cell differentiation and rate of cell growth
What are common characteristics of cancer
- Genetic origin – DNA damage / change and epigenetic changes (histone modifications)
- Accumulation of specific mutations promoting cancer
- Cell division without growth control
- Parasitic in nature
- Require endocrine support of host
- Dependent on host blood supply and nutrition
- Heritable changes which get passed on to daughter cells
- Usually clonal, derived from one single cell
What are the 4 fundamental features to distinguish and characterise benign vs malignant neoplasms
- Differentiation and anaplasia
- Rate of growth
- Local invasion
- Metastasis
Describe differentiation and anaplasia in benign vs malignant
- Benign: In parenchyma fairly normal, well differentiated cells, still fulfil tissue function, mitosis rare but normal
- Malignant: In parenchyma differentiated to completely undifferentiated cells with loss of tissue function, nuclei hyper chromatic and large, several nuclei possible, anaplasia
Describe rate of growth in benign vs malignant
- Benign: Slow growth (months to years) and mitosis is rare but normal
- Malignant: Fast growth, atypical, numerous mitosis, growth rate usually inversely proportional to level of differentiation
Describe local invasion in benign vs malignant
- Benign: Remains localised at site of origin, most are encapsulated but not all
- Malignant: Progressive growth, infiltration, invasion, destruction and penetration of surrounding tissue, no development of well defined capsules
What is metastasis
- Metastasis: Spreading of malignant neoplasms
- Metastases: Secondary implants, originating from a primary lesion, of a different cellular origin (different morphology, colour, cell to cell signalling)
Describe metastasis in benign vs malignant
- Benign: Never
- Malignant: Pathways of dissemination, seeding within body cavities, lymphatic / hematogenious to liver, lungs, veins and arteries (less)
Describe the process of metastasis
- Detachment at tumour site invasion of surrounding connective tissues
- Intravasation into blood / lymph / body cavities, evasion of host defence (immune escape)
- Extravasation from blood vessel into secondary sites
- Proliferation and angioneogenesis (VEGF)
