The formation of tumors can typically be traced back to a single "bad cell," in which mutations have developed on chromosomal DNA. By analyzing the data graphed below, scientists hypothesized that one mutation in a cell's chromosomes is not sufficient to cause cancer.

After analyzing the data within this graph, it is easy to understand why scientists believe the risk of developing cancer increases exponentially with age. Scientists believe that multiple mutations must accumulate in one cell over its lifetime for the cell to cause invasive cancer. You can see from the graph that the incidence of cancer in young people is very low, while quite high in older people. Your cells constantly accumulate mutations as a result of carcinogen exposure, ultraviolet light, or just random chance. If a combination of "bad" mutations develop in the same cell, that cell may be the precursor of cancer.