Commentary on “aTTom”: long-term effects of continuing adjuvant Tamoxifen to 10 years

For more than two decades, five years of adjuvant Tamoxifen remained a standard of care in women with estrogen-receptor-positive (ER+) early breast cancer (EBC). According to the most recent Oxford’s group metaanalysis of 20 trials (n=21,457), five years of Tamoxifen substantially reduced recurrence by 39% and breast cancer mortality by 30% in the treated patients (1). Nevertheless, over 50% of all recurrences in these patients will still occur after completion of five years of adjuvant Tamoxifen, denoting that late relapses are a considerable problem in luminal subtypes of breast cancer (2). Earlier studies extending Tamoxifen course beyond five years have yielded inconclusive results, with two trials reporting a detrimental effect of the longer Tamoxifen treatment [the Scottish Adjuvant Tamoxifen trial (3) and NSABP B-14 (4)] and a 3rd smaller study showing a trend for improved DFS in patients receiving extended Tamoxifen (ECOG study) (5).