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Estrogen replacement therapy and breast cancer survival in a large screening study.

BACKGROUND
Hormone replacement therapy has been associated in some studies with reductions in breast cancer mortality among women who develop this disease. It is unclear whether this association reflects the biologic activity of the hormones or the earlier detection of tumors among hormone users. We examined breast cancer mortality among women who were diagnosed with axillary lymph node-negative and node-positive breast cancer according to the currency of estrogen use at diagnosis.


METHODS
Vital status through June 1995 was determined for 2614 patients with postmenopausal breast cancer diagnosed during the period from 1973 to January 1981. We estimated adjusted hazard-rate ratios (adjusting for tumor size, age, race, Quetelet [body mass] index, and number of positive lymph nodes in women with node-positive disease) and unadjusted cumulative probabilities of breast cancer death over time since diagnosis.


RESULTS
Among patients with node-negative disease, rate ratios for breast cancer mortality associated with current use compared with nonuse at diagnosis were 0.5 (95% confidence interval [CI] = 0.3-0.8) until 144 months after diagnosis and 2.2 (95% CI = 0.9-5.2) thereafter. Mortality was not statistically significantly lower in past users. The cumulative probabilities of breast cancer mortality at the end of follow-up were 0.14, 0.14, and 0.09 in nonusers, past users, and current users, respectively. Among women with node-positive disease, the rate ratios associated with current and past use were both 0.5 until 48 months after diagnosis (95% CI = 0.3-0.8 for current users; 95% CI = 0.3-0.9 for past users) and were 1.1 (95% CI = 0.7-1.7) and 1.8 (95% CI = 1.2-2.7), respectively, thereafter. The cumulative probabilities of breast cancer mortality were 0.32, 0.39, and 0.27 in nonusers, past users, and current users, respectively.


CONCLUSIONS
Patients with breast cancer who were using replacement estrogens at the time of diagnosis experienced reductions in breast cancer mortality, which waned with the time since diagnosis.