From ATLAS to HORIZONTAL: musings on five key trials

The ATLAS trial For decades, 5 years of tamoxifen has been the standard of care for the adjuvant therapy of women with estrogen receptor positive breast cancer, although in recent years for postmenopausal women this treatment has been largely replaced with aromatase inhibitors (AIs). Would extending tamoxifen therapy to 10 years provide further benefit or merely increase toxicity? Do the results of the ATLAS trial, in which nearly 13,000 women were recruited and randomized to receive 5 more years of tamoxifen or to stop tamoxifen at 5 years, provide us with a new standard of care for premenopausal women?