| Question |
Answer |
| Malignancies are |
clonal (derived from a single abnormal cell) |
| Malignicies are Initiated by |
change in cell’s DNA sequence (somatic mutation) |
| Changes in DNA/gene expression result in |
selective growth advantage for some cells |
| A single genetic alteration is usually |
not enough |
| genes involved in cancer process |
Proteins in signaling pathways for cell proliferation |
| genes involved in cancer process |
Cytoskeletal components involved in contact inhibition |
| genes involved in cancer process |
Regulators of the mitotic cycle |
| genes involved in cancer process |
Components of programmed cell death machinery |
| genes involved in cancer process |
Proteins involved in detecting and repairing mutations |
| Different mutations cause cancer |
Activating gain-of-function mutations in one allele of proto-oncogene, Loss of function of both alleles of tumor suppressor gene, Chromosomal translocations that cause misexpression of genes or create chimeric, genes with altered or new function |
| Different types of mutations cause cancer |
Activating gain-of-function mutations in one allele of proto-oncogene |
| Different types of mutations cause cancer |
Loss of function of both alleles of tumor-suppressor gene |
| Different types of mutations cause cancer |
Chromosomal translocations that cause misexpression of genes or create chimeric genes with altered or new function |
| Cytogenetic abnormalities are common in cancer |
Random rearrangements/aneuploidy/loss; Specific translocations are associated with specific cancers; loss of specific chromosomes |
| Chromosomal translocations and proto-oncogenes |
Translocations lead to disruption and rearrangement of genes and their regulating elements; Chimeric (fusion) genes to chimeric proteins; New “gain of function” for proto-oncogene corresponds to activation/deregulation |
| Burkitt lymphoma |
B-cell tumor, Translocation; positioning of MYC proto-oncogene near actively transcribed immunoglobulin heavy chain gene; MYC activation/deregulation; Lymphomatous transformation |
| Chronic myelogenous leukemia and the Philadelphia chromosome |
Involves translocation and Fusion of (ABL) proto-oncogene to BCR gene; Chimeric BCR-ABL; altered protein kinase expression and function of (ABL) oncogene |
| Tumor supressor genes |
prevent tumor development, loss of function leass to cancer |
| gatekeepers |
regulate cell growth |
| caretakers |
genes involved in repairing DNA damage and maintaining genomic integrity (mismatch repair genes) |
| Mechanisms which lead to loss of function |
point mutation in TS gene; deletion of TS gene and surrounding chromosomal material; other structural rearrangements epigenetic events |
| epigenetic events |
transcriptional silencing, alterations in DNA methylation and chromatin configuration |
| In Tumor suppressor genes |
recessive in the cell (both copies of tumor suppressor gene must be mutated to see initiation of malignancy) |
| Tumor suppressor genes |
loss of function may occur in germline or somatic tissue |
| germline mutation confers |
autosomal dominant predisposition to malignancy (familial cancer syndrome) |
| Tumor suppressor genes Examples |
Breast/ovarian – BRCA1/2 and Familial adenomatous polyposis (FAP) |
| Two-Hit Origin of Cancer |
Basis for both hereditary & sporadic cancers; Involves loss of tumor suppressor function; Retinoblastoma (RB) as the model; Loss of both copies of RB1 gene leads to tumor |
| Retinoblastoma (RB) as the model for two hit origin of cancer |
Sporadic cases - 2 somatic mutations same cell; Hereditary cases - inherited (germline) mutation (first hit); second somatic mutation in same cell (second hit) |
| Loss of heterozygosity (LOH) |
Molecular evidence for the existence of a tumor suppressor gene; Involves analysis of DNA polymorphisms near tumor suppressor gene; Testing is done on tumor tissue |
| Loss of RB1 gene function without loss of heterozygosity seen with |
point mutations, gene conversion, transcriptional silencing |
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