The Study: Nearly 3700 women with newly diagnosed and surgically removed hormone receptor-positive breast cancer were enrolled in a massive Italian study to help answer this question. With this kind of enrollment, there was no reason not to go all out with sei post-op treatment arms: “upfront” AI therapy with 5 years of anastrozole [arm 1], exemestane [arm 2], or letrozole [arm 3] or “switch” therapy (a close cousin of intermittent therapy) with 2 years of tamoxifen followed by 3 years of anastrozole [arm 4], exemestane [arm 5], or letrozole [arm 6]. Can you guess the results? There was no difference among any of the arms in terms of the primary endpoint of progression-free survival (PFS), which was ~90% across the board at 5 years. Also to no surprise, grade 1 joint pains were more common with upfront AI therapy (52%) versus switch therapy (42%), and no arm had a non-musculoskeletal grade 3-4 event rate over 2%.
Bottom Line: AI therapy is safe, but unpleasant, in most women with no difference in PFS among different agents. So find the one your patient can tolerate best to optimize what is generally pretty poor compliance.