Not only are there many kinds of cancer, but even cancers that we think of as distinct can act differently in different people. Breast cancer is a case in point. But following initial discouragement upon realizing how differently breast cancer can behave in different women, scientists finally discovered that the distinguishing factor in such cases is the normally protective p53 gene. If there were a molecular category for guardian angels, it would likely be the tumor suppressor genes, including p53.
Cancer is the uncontrolled growth and proliferation of cells.
Normally, the delicate balance of a cell's life is controlled by the interplay between the tumor suppressors, which restrain cell growth, and proto-oncogenes, which stimulate it. Sometimes, however, p53 mutates also. When that happens, it fails to produce the proteins that repress the cell's growth. Patients with mutant p53 become resistant to treatment. In fact, the proliferating cells can develop other mutations and become more and more resistant.