Reproductive determinants of breast cancer in Mexican women.

Abstract

Both the incidence of breast cancer and the proportion of breast cancer cases diagnosed at a late stage have increased dramatically in Mexico since 1980. An epidemiologic study conducted in Mexico City in 1994-95 analyzed the relevance of a set of known reproductive risk factors for breast cancer among Mexican women recruited at four hospitals. Enrolled were 277 cases with histologically confirmed breast cancer (average age 50.1 years) and 201 controls without breast disease (average age 49.7 years); also enrolled were 326 women with benign breast disease (average age 34.2 years). Both age at menarche and at natural menopause were the same (13 and 46 years respectively) in all three groups. Women with breast cancer were significantly older (22 years) than both controls and women with benign breast disease (20 years) at the time of their first birth. Mean duration of breast feeding the first child was significantly longer in controls (8.1 months) than cases (6.5 months). A family history of breast cancer was significantly more prevalent among women with breast cancer (11.9%) than controls (4%). The body-mass index was similar in all three groups as was socioeconomic status. The adjusted odds ratios for breast cancer risk were 1.84 (95% confidence interval (CI) 1.23-2.75) for first birth after compared with before 20 years of age 2.59 (95% CI 1.73-8.42) for nulliparity 0.42 (95% CI 0.22-0.79) for breast feeding after 3 months and 3.29 (95% CI 1.39-7.79) for a family history of breast cancer. These findings are consistent with those of other national and international studies and underscore the importance of breast feeding promotion.