Much research has been devoted to understanding the causes of cancer and finding cures. Unfortunately, there are no simple answers, partly because specific types of cancer have distinct and multiple risk factors and also because it can take a long time for cancers to manifest after exposure to these risk factors. Nevertheless, this review article summarizes the compelling evidence that avoiding dairy products reduces the risk of prostate cancer, avoiding meat decreases the risk of cancers of the colon, rectum, breast, prostate, kidney, and pancreas, consuming soy products during adolescence reduces the risk of breast cancer in adulthood and also decreases the risk of recurrence and mortality for women previously treated for breast cancer, and consumption of fruits and vegetables reduces risk of several common forms of cancer.
 
For additional information, take a look at the data on cancer rates in vegetarians (very little data exists for vegans) provided by Jack Norris, Registered Dietitian and Executive Director of Vegan Outreach. Also, the Physicians Committee for Responsible Medicine (PCRM) argues that a low-fat, fiber-rich vegan diet containing whole grains, vegetables, fruits, and beans, without added fats, can contribute to both cancer prevention and survival.