Several genes called cellular oncogenes (c-onc) or proto-oncogenes have been identified in normal cells which, when activated under certain conditions, could lead to oncogenic
transformation of the cells by reducing the dependence of cells on growth like factors and thus undergo uncontrolled cell division.

Cancer 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. They secrete chemicals that promote the formation of new blood vessels for the cancer cells. This is called angiogenesis. Cells sloughed from such tumors reach distant sites through blood, and wherever they get lodged in the body, they start a new tumor there. This process is called metastasis