INNV-45. DICER1-Mutant Primary Intracranial Sarcoma in an Elderly Patient: A Rare Case with Diagnostic and Therapeutic Implications

Abstract INTRODUCTION Primary intracranial sarcoma, DICER1-mutant (DIS) is a recently classified, high-grade CNS tumor characterized by aggressive behavior and a predilection for pediatric and young adult patients. Its occurrence in older adults is exceedingly rare, and there are no standard treatment guidelines for this population. Management typically involves surgical resection followed by radiation and chemotherapy. We present a rare case of DIS diagnosed in a geriatric patient, managed with surgery, radiation, and immune checkpoint inhibition. Given the patient’s age, frailty, and preferences, chemotherapy was omitted in favor of immunotherapy, reflecting emerging evidence for its potential role in sarcoma management and highlighting the importance of individualized, shared decision-making in rare tumor cases. CASE PRESENTATION We report the case of a 79-year-old man who presented with progressive generalized weakness, nausea, and vomiting. Neuroimaging revealed an enhancing mass in the right parietal lobe. He underwent gross total resection, and subsequent histopathologic analysis with integrated molecular profiling identified a high-grade primary intracranial sarcoma harboring a pathogenic DICER1 mutation. Comprehensive work-up demonstrated no evidence of systemic disease, confirming isolated intracranial involvement. Adjuvant radiation therapy was administered to the resection cavity. Given the patient’s advanced age, medical frailty, and personal preferences, cytotoxic chemotherapy was deferred and immunotherapy with pembrolizumab was initiated. At the time of this report, the patient is alive at approximately 13 months post-diagnosis. DISCUSSION DIS remains exceptionally rare in older adults, with this case representing one of the oldest reported patients to date. In the absence of defined treatment protocols, individualized management is critical. This case highlights the potential role of immune checkpoint inhibitors as a possible alternative to chemotherapy in select DIS patients. It underscores the value of molecular diagnostics and shared decision-making in optimizing care for rare CNS tumors, particularly when standard therapies pose a significant risk due to age or comorbidities.