Risk Factors for Breast Cancer among American Indian Women

Abstract

Objective: This study was designed to identify risk factors associated with breast cancer among American Indian women, as the first step for developing a risk prediction model similar to the Gail model established for non-Hispanic white women. Methods: A case-control study design was undertaken. Cases and controls were selected from among women undergoing mammograms at the Quentin N. Burdick Medical Care Facility (Indian Health Service) in Belcourt ND. For each woman with breast cancer (n=141), two controls were selected when possible (n=278). All women completed a breast cancer risk questionnaire at the time of their mammogram. This questionnaire was the primary source of data, supplemented by electronic and medical chart files. The risk factors examined were those included in the Gail model, including woman’s age, age at first live birth, age of menarche, the number of previous benign breast biopsies, and the total number of first-degree relatives with breast cancer. In addition, body mass index and parity were also collected. Odds ratios and 95% confidence intervals were calculated using logistic regression. Results: I did not find an association for American Indian women in North Dakota between most of the risk factors commonly identified in other populations and breast cancer. The majority of the associations were weakly positive with confidence intervals including the null value. Of all the risk factors examined, nulliparity was the only one that consistently showed a positive significant association. Conclusion: Disparities in breast cancer incidence, mortality and screening among Northern Plains American Indians emphasize the need to better understand the risk factors associated with breast cancer in this population. It is my hope that this study will contribute to the development of a National Cancer Institute Breast Cancer Risk Assessment Tool that reflects the risk of breast cancer among American Indian women. Based on the results of my study, the value of risk prediction models in American Indian communities is uncertain and clinicians should be cautious in using the current Gail Breast Cancer Risk Assessment Tool to inform their American Indian patients of their risk for breast cancer.