Background and methods: The Scottish Adjuvant Tamoxifen Trial (main trial) was initiated in April 1978 to assess the effect of tamoxifen given to patients with breast cancer immediately after mastectomy (or mastectomy plus radiation therapy) (adjuvant arm) or only after the patients had had a relapse (control arm); 1323 patients were randomly assigned (667 to the adjuvant arm and 656 to the control arm). Results have been reported for the follow-up period from 2.5 through 8 years. In this article, we report updated results after a median follow-up of 15 years. If agreeable and eligible, patients who were disease free at 5 years in the adjuvant arm of the main trial were entered into a duration trial and randomly assigned either to stop taking tamoxifen (169 patients) or to continue taking it indefinitely until relapse or death (173 patients). For this update, we analyzed information on death, recurrence, survival, and other malignancies for all but 21 of the 560 living patients from the original and duration trials to determine the probabilities of total survival, systemic relapse of disease, and death from breast cancer. All statistical tests are two-sided.
Results: The beneficial effect of adjuvant tamoxifen given for 5 years on the probability of total survival (P =.006), systemic relapse (P =.007), and death from breast cancer (P =.002) has been maintained through 15 years. No additional benefit was observed in those randomly assigned to continue taking tamoxifen beyond 5 years.
Conclusion: Information from this study suggests that, if adjuvant tamoxifen is given to women with operable breast cancer, it need not be for more than 5 years.