SNPs may cause subtle changes in a group of genes that under normal conditions are latent, i.e., they are switched "off." But when a person is exposed to precarcinogens or carcinogens, they can be switched "on."

Since the proteins from these genes regulate how fast or how slowly the harmful agents are absorbed, bound, metabolized, and excreted from the body, even a small or subtle change in any one of them may alter a person's risk for cancer.

*It is important to remember that the SNP itself does no harm under normal circumstances. Only when a person is exposed to an environmental agent that is carcinogenic, does the SNP exert an influence.