There are large differences among people with similar smoking habits and when they come down with lung cancer. These differences suggest that different people may have different genetic susceptibility to lung cancer from smoking. There are genes that code for cytochrome P450 detoxifying enzymes. Some chemicals are activated by detoxification and become more mutagenic and carcinogenic. It has been shown that the more cytochrome P450 is present the higher the risk of developing lung cancer.
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.