Regeneron presented initial clinical results at IGCS showing durable responses in advanced low-grade serous ovarian cancer (LGSOC) with ubamatamab. In a late-breaking plenary, the company reported a 73% objective response rate and 11-month median progression-free survival among 11 evaluable patients treated with the highest dose of ubamatamab. The report focuses on a disease subset that has limited options and typically low response rates to chemotherapy and endocrine therapy. Regeneron said biomarker selection was not required to see durable outcomes, pointing to MUC16 as a therapeutic target in a hard-to-treat tumor state. Patients in the IGCS update included a median of four prior lines of therapy, and dosing regimens included ubamatamab monotherapy at 800 mg as well as combinations with cemiplimab (Libtayo). For biotech decision-makers, the key near-term watch item is whether these durability and ORR signals replicate across a broader cohort and how response correlates with prior therapies and MUC16 expression.