world cancer report - iarc

Mechanisms of tumour development
The phenotypic changes which a cell undergoes in the
process of malignant transformation is a reflection of the
sequential acquisition of genetic alterations. This multi-step
process is not an abrupt transition from normal to malignant
growth, but may take place over 20 years or more. The mutation
of critical genes, including suppressor genes, oncogenes
and genes involved in DNA repair, leads to genetic instability
and progressive loss of differentiation. Tumours enlarge
because cancer cells lack the ability to balance cell division
by cell death (apoptosis) and by forming their own vascular
system (angiogenesis). The transformed cells lose their ability
to interact with each other and exhibit uncontrolled
growth, invade neighbouring tissues and eventually spread
through the blood stream or the lymphatic system to distant
organs.
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