The ideal duration of adjuvant therapy for women with lower-risk primary breast cancer remains unknown. The National Surgical Adjuvant Breast and Bowel Project (NSABP) B-15 trial, reported more than 20 years ago, found no difference in outcomes between six cycles of cyclophosphamide, methotrexate, and fluorouracil and four cycles of doxorubicin plus cyclophosphamide (AC)—although some believed that the AC arm might have fared better had they received six cycles of AC.