 One of the reasons it's so difficult to study the relationship between diet and cancer is because many dietary behaviors are associated with non-dietary behaviors. For example, the reason we used to think coffee drinking caused cancer was because people who drink coffee are more likely to have a cigarette, in the other hand. When you factor that out, though, for example, by looking at just non-smokers who do or don't drink coffee, we find that if anything, coffee consumption may reduce the total cancer incidence. Not by much, but overall, according to the latest review, an increase in consumption of one cup of coffee per day was associated with about a 3% reduced risk of cancers, especially bladder cancer, breast cancer, mouth, colorectal endometrial, esophageal, liver, leukemia, pancreatic, and prostate cancers. Coffee beans aren't really beans, but one is, after all, soaking a powdered seed in some water, so a reduction in cancer risk? Not that surprising.