OBJECTIVE: Diabetes has been associated with an increased risk of breast cancer in several epidemiologic studies. Age at diabetes onset may be an important modifier of risk, with younger age at diabetes having a protective effect against breast cancer in some studies. No studies have been able to adequately assess the relationship between diabetes and breast cancer in Hispanic women, a population with a high prevalence of diabetes. We investigated the association between diabetes and breast cancer risk in a population-based case-control study of Hispanic and White, non-Hispanic (WNH) women living in Arizona (AZ), New Mexico (NM), Colorado (CO) and Utah (UT). METHODS: Breast cancer cases diagnosed in 1999-2004 were identified through state cancer registries (n=1,526 WNH; n=798 Hispanics). Controls were frequency-matched to cases on age and ethnicity, and selected from either driver’s license records (NM and UT) or commercial mailing lists (AZ and CO) for those ages <=65, and social security records for those ages 65+ (n=1,599 WNH; n=924 Hispanics). History of diabetes was assessed through interviewer-administered questionnaire. Associations between diabetes and breast cancer were calculated using logistic regression, adjusting for age, study site, menopausal status, body mass index (BMI), number of full-term pregnancies, and age at first pregnancy. RESULTS: Diabetes of any type was reported by 11.7% of cases and 13.1% of controls, and was not associated with breast cancer overall (odds ratio (OR)=0.96, 95% confidence interval (CI)=0.80-1.15). Diabetes was more prevalent among Hispanics (19%) than WNH (9%), although there was no association with breast cancer in either ethnic group. No differences in risk were observed after stratification by age at diabetes onset. Gestational diabetes, reported by 3.3% of cases and 4.2% of controls, tended to be protective against breast cancer overall (OR=0.71, 95% CI=0.48-1.05). This effect depended on age at gestational diabetes: women with a history of gestational diabetes at ages <=35 years had a statistically significant 44% reduction in breast cancer risk (OR=0.56, 95% CI=0.39-0.82), while women with gestational diabetes at older ages experienced no risk reduction (OR=1.32, 95% CI=0.71-2.47). The inverse association between gestational diabetes at age <=35 and breast cancer was present in both WNH (OR=0.69, 95% CI=0.43-1.10) and Hispanics (OR=0.38, 95% CI=0.20-0.73), and consistently observed for both premenopasual and postmenopausal women, and across strata of BMI. CONCLUSION: History of gestational diabetes, especially at younger ages, may be protective against breast cancer in white, non-Hispanic and Hispanic women. Other types of diabetes, although prevalent among Hispanics, were not associated with an increase in breast cancer risk.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA