Extended Adjuvant Intermittent Letrozole Versus Continuous Letrozole in Postmenopausal Women With Breast Cancer (SOLE): A Multicentre, Open-Label, Randomised, Phase 3 trial
Colleoni M, Luo W, Karlsson P, et al; SOLE Investigators Lancet Oncol. 2018;19:127-138
Study Summary
The optimal duration of adjuvant therapy for postmenopausal women with estrogen receptor-positive (ER+) early-stage breast cancer is unknown. Adjuvant therapy with aromatase inhibitors (AIs) after 5 years of tamoxifen has been shown to improve outcomes. However, the magnitude of benefit for women who were previously treated with AIs has not been well characterized, with one study (the MA.17R trial) showing a possible benefit[1] and another (NSABP B-42) showing no improvement.[2] In addition, animal models of breast cancer have shown that resistance to AIs can be overcome by withdrawal of therapy followed by reintroduction.
The SOLE study was designed to explore whether extended intermittent use of an AI, letrozole, would improve breast cancer outcomes compared with continuous use in postmenopausal women. It was a multicenter, open-label, phase 3 randomized, controlled trial that enrolled 4884 women between 2007 and 2012 at 240 sites in 22 countries. Participants were postmenopausal women with ER+, node-positive breast cancer who had undergone local therapy and had completed 4-6 years of adjuvant therapy and clinically had "no evidence of disease." Women were randomly assigned to a continuous schedule or to an intermittent schedule consisting of 9 months of use, followed by a 3-month drug holiday for years 1-4 and continuous use for year 5 of the study. The primary endpoint was disease-free survival.
