This epidemiologic case-control study examined the relationship between replacement estrogen use and breast cancer risk in 2 population groups in Hawaii. No significant associations were observed when 161 Caucasian cases were compared with either their neighborhood controls (RR = 0.9; 95% CI = 0.5-1.3)5 or their hospital controls (RR=0.7; 9 5 2 CI=O.4 to 1.1) and when 183 Japanese cases were compared with either their neighborhood controls (RR = I . I ; 95% CI = 0.7-1.6) or their hospital controls (RR = I .O; 95% Cl=O.6-1.4). The results indicate that the use of replacement estrogens cannot account for the large difference in breast cancer incidence between the 2 Hawaiian ethnic groups. However, further data analysis involving neighborhood controls was suggestive of a possible increase in breast cancer risk with estrogen use for certain sub-groups of women who are at high risk for the disease. These included estrogen users with a family history of breast cancer or a history of benign breast disease. These findings are in agreement with other studies which have used non-hospitalized controls. Because the numbers of cases in this study are not substantial, it is recommended that a large population-based case-control study be undertaken to clarify the relationship between breast cancer risk and replacement estrogen use, especially in sub-groups of women at high risk for the disease.
Many studies have looked at the association of breast cancer with the use of replacement estrogens. They have either noted the lack of any association (Kelsey