cancer

Biological properties of cancer cells

When normal cells are damaged beyond repair, they are eliminated by apoptosis (A). Cancer cells avoid apoptosis and continue to multiply in an unregulated manner (B).

In a 2000 article by Hanahan and Weinberg, the biological properties of malignant tumor cells were summarized as follows:^[40]

• 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.