In this study, breast-feeding was associated with a reduced risk of childhood acute leukemia. If confirmed in additional epidemiologic studies, our findings suggest that future epidemiologic and experimental efforts should be directed at investigating the anti-infective and/or immune-stimulatory or immune-modulating effects of breast-feeding on leukemogenesis in children.

Although intake of well-done red meat has been associated with an increased risk of breast cancer (1), it is unclear what component(s) of well-done red meat is associated with this risk. Meats cooked to well-done at high temperatures contain heterocyclic amines (HCAs), such as 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) (2-9). The amounts of these compounds vary according to cooking technique, temperature, cooking time, and type of meat (10,11). Although PhIP administered orally can induce mammary gland carcinomas in rats (12)(13)(14), the association of HCAs with human breast cancer is unclear. Two studies have investigated the association between meat-cooking methods and breast cancer. One study (15) did not obtain information on the degree of meat doneness, from which levels of HCA can be estimated, and the other study (16) used HCA estimates from laboratory-cooked meat samples from one country and subjects from a different country.We used a newly created database [for details, see (10) and (11)] to estimate HCAs in a breast cancer casecontrol study of 41 836 cohort members participating in the Iowa Women's Health Study (1). Of the selected subjects, 273 case patients (60% of all women with breast cancer diagnosed from 1992 through 1994) and 657 control subjects (75% of randomly selected cohort members who were alive and free of cancer on January 1, 1992, and participated in the 1992 follow-up survey) participated in this study. All subjects completed a self-administered foodfrequency questionnaire that included validated questions on frequency of intake and cooking techniques of 15 meat items. The participants reported their usual preference for level of doneness by using a series of color photographs that represented increasing levels of doneness of a hamburger patty and beef steak (four photographs for each) as well as bacon (three photographs) (10,11).We estimated HCA intake by use of our database (10,11,17) and the responses from the food-frequency questionnaire. First, we estimated gram consumption by frequency, portion size, cooking technique, and doneness level. Second, we derived HCA intake by multiplying grams of meat by the HCA concentration measured for each cooking technique/doneness level for that meat type and summed across the three meats. To estimate the doneness levels, we added the gram amounts for "rare/ medium," "well-done," and "very welldone" steak, hamburger, and bacon. Dietary intakes of each HCA and each type of red meat were lower among the control subjects than among the case patients, with the case patients consuming 50% more PhIP (Table 1).Odds ratios (ORs) were computed with unconditional logistic regression (18), with test of trends based on continuous variables (Table 2). The association between HCA and risk was determined for each HCA individually and with adjustment for the other HCAs. ORs for DiMeIQx, MeIQx, and PhIP are presented in two ways: i...