Roche reported positive Phase III results for its oral selective estrogen receptor degrader (SERD) giredestrant in the adjuvant setting for estrogen-receptor–positive, HER2-negative early breast cancer, meeting the Lidera study’s primary endpoint by extending invasive disease-free survival versus standard endocrine therapy. Roche said a clear positive trend on overall survival was observed but noted it is too early to claim a definitive survival benefit. The data represent the first large-scale adjuvant win for an oral SERD and could broaden use beyond current late-stage indications if regulators accept the benefit-risk profile. The readout intensifies competition among oral SERDs—AstraZeneca and Lilly are key peers with trials pending—and could shift adjuvant practice patterns if confirmed. Market and equity reactions showed notable uplift for SERD-focused peers that could benefit from accelerating class validation.