An international team of researchers has released the results of a major clinical trial of a new hormonal drug, giredestrant, developed for the treatment of early-stage hormone receptor–positive, HER2-negative breast cancer. The study, published in The New England Journal of Medicine, is already being described as one of the most significant breakthroughs in the field in decades.

The trial included 4,170 patients who had undergone surgery and, when required, chemotherapy. They were then assigned to receive either giredestrant or one of four standard hormonal therapies, including tamoxifen and aromatase inhibitors. Treatment continued for up to five years, with a median follow-up of 32.3 months at the time of analysis.

The results were striking: patients taking giredestrant experienced about a 30% reduction in the risk of recurrence compared with those receiving standard therapy. The new drug was also associated with fewer distant metastases. At the same time, its side-effect profile was similar to that of standard treatments — the most common reactions were moderate joint pain, hot flashes, and headaches. Fewer patients in the giredestrant group discontinued treatment due to adverse effects than in the control group.

Researchers emphasize that these findings may mark the beginning of a new era in adjuvant hormonal therapy. Since roughly 70% of all breast cancers are hormone receptor–positive, a more effective and potentially more tolerable medication could substantially reduce recurrence rates and improve long-term outcomes.

If confirmed in ongoing follow-up, giredestrant may become a new standard of care, replacing regimens that have been in use for more than two decades.