Prolonging Tamoxifen Therapy for Primary Breast Cancer. Findings from the National Surgical Adjuvant Breast and Bowel Project Clinical Trial.

OBJECTIVE: To determine whether prolonging the duration of tamoxifen administration beyond the cessation of a combined chemotherapy regimen benefits patients with primary breast cancer with positive findings in axillary nodes who benefit initially from the combined regimen. DESIGN: Nonrandomized, nonconcurrent cohort study. SETTING: National Surgical Adjuvant Breast and Bowel Project, conducted in 68 institutions in North America. PATIENTS: Women were included if they had breast cancer with positive nodes and were aged 49 years or less with both estrogen and progesterone receptor levels of 10 fmol or more, aged 50 to 59 years with progesterone receptor levels of 10 fmol or more, or aged 60 to 69 years. Two cohorts were compared: patients who were randomly assigned to the tamoxifen arm of the adjuvant chemotherapy trial (randomized patients) and women who were added to this arm after randomization had ceased (registered patients). Three hundred seventy-seven women in each group who were disease free at the end of the initial 2-year treatment period were followed for an additional 3 years. INTERVENTIONS: All received melphalan, fluorouracil, and tamoxifen (10 mg twice daily by mouth) for 2 years. Registered patients (but not randomized patients) were offered tamoxifen for a third year after the initial 2-year treatment period, and 273 (72%) agreed. MEASUREMENTS AND MAIN RESULTS: Women receiving a third year of tamoxifen had a better disease-free survival rate (odds ratio, 1.54; 95% confidence interval, 1.14 to 2.07; p = 0.004) and survival rate (odds ratio, 1.56; 95% Cl, 1.02 to 2.37; p = 0.04) through their fifth postoperative year. Women aged 50 years or more benefited, but those aged 49 years or less did not. CONCLUSIONS: The benefit of tamoxifen given to tamoxifen-responsive patients in conjunction with melphalan and fluorouracil appears to be enhanced when the tamoxifen treatment is continued beyond cessation of treatment with these agents