We know that some exposures increase the risk of cancer, but we don't know which specific combinations of environmental factors on the outside of the body combine with gene changes on the inside to lead to cancer. We don't know why two persons can have very similar environmental exposures, yet one gets cancer and the other does not. A number of individual factors are involved and there are complex relationships among them.

The individual chance that someone will develop cancer in response to a particular, single environmental exposure depends on how long and how often that person was exposed. It also depends on the person's:

• exposures to certain environmental factors (including diet, hormones)
• genetic makeup
• age and gender

< Previous  |  Index  |  Next Slide >