Breast cancer is the third most common cancer world-wide. The cause of breast cancer is not well understood. It has been established that women who menstruate early, have late first babies, go through menopause late, and are obese are at high risk for developing breast cancer. These associations are probably all due to hormonal factors. These genes are known to be tumor suppressing genes.
Colorectal cancer is the second most common cancer in developed countries.
It is much rarer in developing countries. Nutritional factors are being studied due to the variation in disease rates between populations with different diets. There is also a hypothesis that the contents of the colon and rectum could affect the risk of cancer. Epidemiological studies have been done on the affects of meat, animal fat, fiber, fruits, and vegetables. The results of the studies have varied.