Biological properties of cancer cells

In a 2000 article by Hanahan and Weinberg, the biological properties of malignant tumor cells were summarized as follows:^[36]

• Acquisition of self-sufficiency in growth signals, leading to unchecked growth.
• Loss of sensitivity to anti-growth signals, also leading to unchecked growth.
• Loss of capacity for apoptosis, in order to allow growth despite genetic errors and external anti-growth signals.
• Loss of capacity for senescence, leading to limitless replicative potential (immortality)
• Acquisition of sustained angiogenesis, allowing the tumor to grow beyond the limitations of passive nutrient diffusion.
• Acquisition of ability to invade neighbouring tissues, the defining property of invasive carcinoma.
• Acquisition of ability to build metastases at distant sites, the classical property of malignant tumors (carcinomas or others).

The completion of these multiple steps would be a very rare event without :

• Loss of capacity to repair genetic errors, leading to an increased mutation rate (genomic instability), thus accelerating all the other changes.

These biological changes are classical in carcinomas; other malignant tumor may not need all to achieve them all. For example, tissue invasion and displacement to distant sites are normal properties of leukocytes; these steps are not needed in the development of leukemia. The different steps do not necessarily represent individual mutations. For example, inactivation of a single gene, coding for the p53 protein, will cause genomic instability, evasion of apoptosis and increased angiogenesis. Not all the cancer cells are dividing. Rather, a subset of the cells in a tumor, called cancer stem cells, replicate themselves and generate differentiated cells