Regeneron presented early efficacy data for ubamatamab in advanced low-grade serous ovarian cancer (LGSOC), a biologically distinct subtype with limited treatment options. In a late-breaking IGCS plenary presentation, the company reported a 73% objective response rate with an 11-month median progression-free survival in 11 heavily pretreated patients at the highest ubamatamab dose. Data were shown for an LGSOC subset within a larger program, including patients treated with ubamatamab monotherapy and in combination with cemiplimab (Libtayo). Regeneron emphasized durability of responses so far and highlighted MUC16 as the therapeutic target. Importantly for trial strategy, responses were reported without biomarker selection, an approach that could broaden the patient addressable market if confirmed in larger cohorts. The update adds to the growing effort in serous ovarian cancer to translate tumor antigen targeting and immune activation into clinically meaningful benefit for patients underserved by chemotherapy and endocrine approaches.