Cancer is one of the most dreaded diseases of human beings and is a major cause of death all over the globe. More than a million Indians suffer from cancer and a large number of them die from it annually. The mechanisms that underlie development of cancer or oncogenic transformation of cells, its treatment and control have been some of the most intense areas of research in biology and medicine. Transformation of normal cells into cancerous neoplastic cells may be induced by physical, chemical or biological agents.Early detection of cancers is essential as it allows the disease to be treated successfully in many cases. Cancer detection is based on biopsy and histopathological studies of the tissue and blood and bone marrow tests for increased cell counts in the case of leukemias. 

The characteristics of cancer cells include :

(i) These do not undergo differentiation .

(ii) These continue dividing ceaselessly 

(iii) These invade the neighbouring tissue and dislocate their functions.

(i) , (ii) and (iii) .

In our body, cell growth and differentiation is highly controlled and regulated. In cancer cells, there is breakdown of these regulatory mechanisms.

Normal cells show a property called contact inhibition by virtue of which contact with other cells inhibits their uncontrolled growth. Cancer cells appears to have lost this property. As a result of this, cancerous cells just continue to divide giving rise to masses of cells called tumors.

The malignant tumors, are a mass of proliferating cells called neoplastic or tumor cells. These cells grow very rapidly, invading and damaging the surrounding normal tissues.

As these cells actively divide and grow they also starve the normal cells by competing for vital nutrients.