A Delicate Balance: Immunotherapy for Endometrial Cancer in a Patient With Multiple Sclerosis.

Multiple sclerosis (MS) is a chronic immune-mediated disease that may complicate oncological management, particularly when immune checkpoint inhibitors (ICIs) are indicated. Evidence regarding the safety of ICIs in patients with pre-existing MS remains limited, especially in older patients and in the first-line treatment of endometrial cancer (EC). We present the case of a 71-year-old woman with relapsing-remitting MS (radiologically stable for > 12 months) and stage IIIC1 mismatch repair-deficient/microsatellite instability-high EC who was treated with first-line carboplatin-paclitaxel combined with programmed cell death protein 1 (PD-1) inhibitor dostarlimab. Ozanimod, which had been used to manage her MS, was temporarily discontinued prior to chemotherapy. No clinical relapses or new magnetic resonance imaging (MRI) activity were observed during combination therapy or throughout a 12-month interim follow-up. Dostarlimab maintenance therapy is ongoing. This case suggests that ICIs may be cautiously integrated into the treatment of selected patients with MS and advanced EC when baseline neurological stability, patient age, and prior disease-modifying therapy are carefully considered. Close interdisciplinary collaboration and structured neurological monitoring are essential. Longer follow-up is required to confirm long-term neurological safety.