Quoted from Living Downstream:
[I]f heredity is suspected as the main cause of a certain kind of cancer, we would not expect to see its incidence rise rapidly over the course of a few human generations because genes cannot increase their frequency in the population that quickly.
[I]n 1973, 99 out of every 100,000 women living in the United States were diagnosed with breast cancer. By 1998, the incidence had risen to 141 out of 100,000. The rate of breast cancer has declined since then and in 2005 stood at 118. Thus, we are still standing on higher ground than we were in 1973, when the federal registry was founded, but we seem to be in a better place than we were a decade ago.
These numbers are also age-adjusted. That is, the data from all the differently aged people from any given year are weighted to match the age distribution of a particular census year. Thus standardized, the statistics from various years can be compared to each other. In this way, we know that the 43 percent rise in breast cancer between 1973 and 1998 did not happen because the population was aging.
Steingraber, Sandra. Living Downstream: An Ecologist’s Personal Investigation of Cancer and the Environment (p. 36, 37). Da Capo Press. Kindle Edition.