Coffee and methylxanthines and breast cancer: a case-control study.

A dietary case-control study based on 818 newly diagnosed breast cancer (BC) patients was conducted in Israel between 1975 and 1978. The role of coffee and total methylxanthine intake from coffee, tea, cola, chocolate, and cocoa drinks was evaluated in the BC patients as compared to that in two matched control populations [surgical controls (SC) and neighborhood controls (NC)]. Because it has been suggested that caffeine enhances mammary carcinogenesis in rats fed high polyunsaturated fat diets, analysis was done also in relation to fat consumption. When comparison was done to both matched control groups, a nonsignificant negative association was found between consumption of cups of coffee and BC (odds ratios of greater than or equal to 4 cups of coffee/day vs. less than or equal to 1 per week = 0.6 for BC/NC and 0.7 for BC/SC). This association was observed in all 3 ethnic subgroups studied. The pattern was stronger among the high-fat consumers after controlling for several hormonal confounding factors (two-tailed P-value for linear trend = 0.06 for SC and P = 0.05 for NC). In addition, when the consumption of methylxanthine of BC patients was compared to that of benign breast patients, adjusted by age and ethnic group, a diminished risk was found (odds ratio for BC of the highest level of methylxanthine vs. lowest level = 0.59).