GENES AND CANCER

                 Cancer refers to a set of diseases in  which cells somehow escape the control mechanisms that normally keep a check on their growth or signal pathways or receptors. The sources of mutations can be several, ranging from environmental influences viz. UV radiation or chemical carcinogens viz, food additives, preservatives, pesticides, insecticides, etc. or X-rays and other high energy radiation to certain cancer-causing viruses or even tobacco smoke and air pollutants.

 

                  The breakthrough in understanding cancer came in 1911, when Peyton Rous, an American

 virus pathologist, discovered a virus that causes cancer in chickens. Since the, scientists have discovered a number of tumor viruses that cause cancer in various animals including humans e.g.

Epstein-Barr  virus - Burkitt's lymphoma

Papilloma virus -Cancer of cervix

HTLV-1- a type of adult leukemia

*Retro virus -HIV, (AIDS)

Corona virus - Severe Acute Respirator Syndrome (SARS)

         Research on these tumor viruses lead to the discovery of cancer-causing genes called oncogenes (derived from the Greek word " Onico" meaning tumor) in certain retroviruses. Subsequently, close relatives of these oncogenes were also found in the genomes of animals and humans. The unmutated or normal version of these genes is called proto -oncogenes which codes for proteins stimulates normal cell growth an division. These genes can regulate growth factors or receptors or signals molecules during cell cycle, Now, if these normal or protooncogenes undergo genetic changes, i.e., mutations, they are transformed into oncogenes. This disrupts the cell cycle and therefore can lead to cancer.

         However, there are also some cellular genes that normally function to inhibit cell division. Such genes are called tumour-suppressor genes because these prevent uncontrolled cell growth. As, transformation of proto-onogenes to oncogenes can cause cancer by mutation, similarly mutation of tumour-suppressor genes can also lead to malignant growth, e.g., Retinol blastoma (Wilm;s tumour)

This does not mean that cancer can be caused only by genes, but it also arise spontaneously by non-inheritable causes.