Optimal management of luminal breast cancer: how much endocrine therapy is long enough?

Patients with early estrogen receptor-positive breast cancer are at continuous risk of relapse even after more than 10 years of follow up. Currently, no biomarker that identifies patients for early versus late recurrence, or one that selects patients or tumors for longer versus shorter durations of endocrine therapy (ET) is available and a crucial question is how to properly select patients who could be spared extended ET or those who require it. In the last 20 years more than 40,000 women were enrolled in randomized trials to answer the question of optimal duration of ET. According to the results of these studies extended adjuvant ET is more effective than standard 5 years of adjuvant ET. Extended ET in patients who remain premenopausal after 5 years of adjuvant tamoxifen is still tamoxifen for another 5 years. Extended ET with aromatase inhibitors (AIs) should be offered to postmenopausal women with substantial residual risk of relapse after completing 5 years of tamoxifen therapy. Extension of AI treatment to 10 years resulted in significantly better 5-year disease-free survival including disease recurrence local/distant or the occurrence of contralateral breast cancer events. Currently, new therapeutic targets are under investigation, but the beneficial effect of prolonged treatment for high-risk patients, identified by using multigenomic tests, remains unclear. Thus, further studies need to be performed to confirm the advantage of extended adjuvant ET in selected patients.