Effects of adjuvant tamoxifen over three decades on breast cancer–free and distant recurrence–free interval among premenopausal women with oestrogen receptor–positive breast cancer randomised in the Swedish SBII:2pre trial

Abstract

AimsThe primary aim was to compare 2 years of adjuvant tamoxifen versus no systemic treatment in premenopausal patients with oestrogen receptor (ER)–positive tumours, regarding breast cancer–free interval (BCFi) and distant recurrence–free interval (D-RFi), with 30 years of follow-up and for specified intervals. Moreover, we aimed to investigate the effects of adjuvant tamoxifen on the incidence of secondary malignancies and survival after distant recurrence. MethodsPremenopausal patients with primary breast cancer were randomised to 2 years of tamoxifen (n = 277) or no systemic treatment (n = 287), irrespective of ER status. Information regarding events was collected by a review of medical records and from national registers. ResultsThe median follow-up for all patients without events was 28 years, and only four of the patients alive had a follow-up of <20 years. With 30 years of follow-up, tamoxifen prolonged BCFi in the intention-to-treat population (hazard ratio [HR] = 0.76, 95% confidence interval (CI) 0.61–0.94, p = 0.011) compared with no treatment. In patients with ER-positive tumours (n = 362), tamoxifen prolonged BCFi (HR = 0.62, 95% CI 0.47–0.82, p = 0.001) and D-RFi (HR = 0.73, 95% CI 0.54–0.99, p = 0.043). The positive effect on BCFi was significant also for the interval >15–30 years (HR = 0.53, 95% CI 0.28–0.98, p = 0.042). For patients with ER-positive tumours who were diagnosed with distant recurrence (n = 165), survival after distant recurrence was shorter among tamoxifen-treated patients (median, 29 months versus 43 months). The incidence of contralateral breast cancer was 42% lower in the tamoxifen group (HR = 0.58, 95% CI 0.35–0.96, p = 0.035), whereas no differences were observed regarding other secondary malignancies. ConclusionsWith three decades of follow-up, 2 years of adjuvant tamoxifen reduced the incidence of breast cancer–related events and distant recurrence, and the carryover effect seems to extend beyond 15 years. Moreover, adjuvant tamoxifen seems to be associated with shorter survival after diagnosis of distant recurrence.