Cancer cells and precancerous cells are so common that nearly everyone by middle age or old age is riddled with them, said Thea Tlsty, a professor of pathology at the University of California, San Francisco. That was discovered in autopsy studies of people who died of other causes, with no idea that they had cancer cells or precancerous cells. They did not have large tumors or symptoms of cancer. “The really interesting question,” Dr. Tlsty said, “is not so much why do we get cancer as why don’t we get cancer?”
The earlier a cell is in its path toward an aggressive cancer, researchers say, the more likely it is to reverse course. So, for example, cells that are early precursors of cervical cancer are likely to revert. One study found that 60 percent of precancerous cervical cells, found with Pap tests, revert to normal within a year; 90 percent revert within three years.