Exceptional Response to a Single Dose of Pembrolizumab as Salvage Therapy for Metastatic Adrenocortical Carcinoma.

A 19-year-old woman presented with severe hypertension, hypokalemia, and clinical signs of Cushing syndrome (CS). Computed tomography imaging revealed a large left adrenal mass encasing a major vessel, a left renal lesion, a right ovarian teratoma, and multiple pulmonary micronodules. F-fluorodeoxyglucose positron emission tomography (18-FDG-PET) showed hypermetabolism in the adrenal mass, lung nodules, and teratoma. Biochemical work-up confirmed adrenocorticotropin-independent CS and elevated adrenal androgens, consistent with metastatic, unresectable adrenocortical carcinoma. The patient was started on mitotane and metyrapone, followed by 8 cycles of etoposide-doxorubicin-cisplatin plus mitotane. Despite treatment, the disease progressed. Adrenal biopsy revealed high tumor-infiltrating lymphocytes, low tumor mutation burden, low programmed death-ligand 1 expression, and microsatellite stability. Germline testing identified a pathogenic variant, confirming Li-Fraumeni syndrome. A single dose of pembrolizumab was administered as salvage therapy but led to grade 3 immune-related hepatitis and prolonged hospitalization, requiring cessation of both pembrolizumab and mitotane. Remarkably, a follow-up scan 3 months later showed 60% regression of the adrenal mass, stable renal and ovarian lesions, and resolution of lung nodules. The patient underwent complete surgical resection, achieving full remission. More than 1 year later, she remains disease free.