Mammographic findings and family history risk for breast cancer in American Indian women

Access to annual screening mammography among American Indians is limited, and data regarding breast cancer risk factors or mammography in these women are scarce. Although average breast cancer mortality rates are lower than those of all races in the United States, rates vary widely between tribes (3.9-24.6/100,000; 1991-1993), with the highest mortality rates in the Aberdeen Area of the Indian Health Service (AAIHS). A retrospective study of 351 American Indian women in the AAIHS (North Dakota, South Dakota, Iowa, and Nebraska) reviewed screening mammograms, mammographic records, and family history for breast cancer and determined mammographic density. A dense mammogram was defined as one with >50% mammographic density. Rates of dense breasts were compared with a database of non-American Indian women of Ann Arbor, Michigan. Of 351 women, 11.1% had abnormal mammograms, and 0.8% had breast cancer. Family history of breast cancer in ≤1 first-degree relative occurred in 10.0% of women. Dense breasts occurred in 25% of women ages 40- 49 years and in 11.4% of women ages 50-59 years. In non-Indians, 67% of women ages 40-49 years (P = 0.000001) and 25% of women ages 50-59 years (P = 0.068) had dense breasts. Rates of positive family history, abnormal mammograms, and detected malignancy were similar to other published rates, which validates the importance of breast cancer screening in this group. A statistically significant smaller proportion of American Indian women had dense mammograms, suggesting that mammography may be more sensitive in the detection of breast cancer in women in the AAIHS region.