What is Cancer?

Cancer is an uncontrolled growth of cells. It is responsible for 13% of deaths worldwide (an estimated 7.7 million deaths in 2007). Cancer results from mutation in genes controlling cell growth, differentiation and death. Uncontrolled growth is a character of cancer and of benign neoplasms. Anaplasia, invasion and metastasis sets cancer apart from a benign tumour. Cancer is lethal because of it's ability to metastasize. Metastasis kill 90% of cancer patients.

The genes causing cancer
Why should the human genome have genes capable of causing cancer? Were it not for these genes a zygote would not develop into a foetus. Normal development depends on an adequate number and appropriate type of cells populating each developing organ. Cell division, tissue invasion, migration of these cells to sites distant from the origin and loss of unwanted cells are necessary for normal embryonic development. These process are very precise. This is evident from the extremely low levels of conginital anomalies. Cancer results when these processes get derranged.

Cancer causing genes fall into two categories, oncogenes and tumour supressor genes. About 1% of the genome (over 200 genes) are involved in malignant transformation. Some commonly mutated cancer genes and their normal function are listed below (oncogenes in blue, tumour suppressor genes in red).

1. Growth Factors




1. PDGFB: Platelet Derived growth factor beta.




2. Receptors




1. EGFR, ERBB2: Epithelial growth factor receptors


2. PDGFA, PDGFB: Platelet derived growth factor receptors


3. FLT1, KDR, FLT4: Vascular endothelial growth factor receptor




3. Signal Transduction




1. Small G Proteins: HRAS, KRAS, NRAS


2. MAPK/ERK Pathway: RAF1


3. JAK/STAT: JAK2, STAT5A/B


4. Hedgehog Pathway:PTCH1, SMO, SUFU




4. Transcription factors




1. MYC




5. Genes involved in maintaining DNA integrity:
   




1. Repair of double stranded DNA breaks: BRCA1, BRCA2


2. Mismatch repair genes: MLH1, MSH2, MSH6, PMS1, PMS2




6. Cell cycle Regulators




1. CCND1: Cycline D1 Gene


2. RB1: Retinoblastoma tumour suppressor gene




7. Genes involved in apopotosis




1. TP53:




8. Cytoskleton




1. APC:


2. NF2: