Exacerbation of paraneoplastic cerebellar degeneration by immune checkpoint inhibitor use in endometrial cancer.

Background: Immune checkpoint inhibitors (ICIs) have transformed the management of advanced and recurrent endometrial carcinoma (EC). ICI therapy can be associated with complex, multisystemic immune-related adverse events (irAEs), which present new challenges in gynecologic oncologic care management. Anti-Yo-positive paraneoplastic cerebellar ataxia (PCA) is a rare syndrome that can be associated with gynecologic malignancies that presents with subacute gait ataxia with imbalance and falls and can demonstrate cerebellar atrophy on imaging. Case: Here we describe a patient with stage IVB uterine carcinosarcoma who developed subacute progressive gait ataxia with falls while on maintenance dostarlimab. Neurological workup revealed the presence of anti-Yo antibodies, suggesting a paraneoplastic neurological syndrome (PNS), specifically paraneoplastic cerebellar degeneration (PCD). Dostarlimab was omitted from her subsequent course of treatment, and immunosuppression started with initial improvement followed by stabilization of symptoms. Conclusion: This case demonstrates the protean nature and sometimes subtle onset of toxicities associated with these agents, requiring complex coordination of care and multidisciplinary management, particularly as these agents become increasingly important in the management of gynecologic malignancies.