EP1733 - LBA_ECE_1473 - The role of pembrolizumab immunotherapy in metastatic adrenocortical carcinoma: a case series study

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Abstract Background Adrenocortical carcinoma (ACC) is a rare endocrine malignancy with a poor prognosis in advanced stages. Standard first-line treatment for metastatic disease involves mitotane and cytotoxic chemotherapy (EDP-M); however, therapeutic options following progression are limited. Immunotherapy with immune checkpoint inhibitors, such as the anti-PD-1 agent pembrolizumab, has shown potential in solid tumors, particularly those with high microsatellite instability (MSI-H) or deficient mismatch repair (dMMR). This study presents the clinical experience, safety, and outcomes of patients treated with pembrolizumab at a specialized Endocrine Unit of a University Hospital. Methods This retrospective observational case series study analyzed a cohort of seven adult patients with metastatic ACC followed between 2020 and 2026. Among them, three patients receiving pembrolizumab as salvage therapy for advanced disease were evaluated. Data collection included demographic profiles, clinical and histopathological characteristics, progression-free survival (PFS), overall survival (OS), and treatment-related toxicity. Results Case 1: A 30-year-old female with functional, symptomatic ENSAT stage IV ACC (pulmonary, hepatic, bone metastases) and Ki-67 35%-40% (Weiss score 8). Following surgery, adrenolytic therapy, and chemotherapy, pembrolizumab was initiated three years post-diagnosis. Treatment was discontinued after a single administration due to severe drug-induced hepatitis. Although a partial reduction in pulmonary metastases occurred, the brief treatment duration precluded a definitive attribution of this response to immunotherapy. Case 2: An 89-year-old female with functional ENSAT stage IV ACC (pulmonary, diaphragmatic, nodal, perirenal involvement) and a Ki-67 index of 50% (Weiss score 8), received pembrolizumab postoperatively alongside mitotane as salvage therapy. Efficacy could not be assessed as the patient succumbed shortly after initiation; death was attributed to rapid disease progression. Case 3: A 56-year-old female with symptomatic ENSAT stage IV oncocytic ACC (renal, hepatic, IVC involvement) with low grade malignancy (Weiss score 4, Ki-67 15%). Following surgery and standard therapies, she received pembrolizumab for two years. She achieved a sustained initial response with disease progression occurring 2 years later. Conclusion Pembrolizumab demonstrates heterogeneous outcomes in metastatic ACC. While it may provide prolonged disease control in selected patients. The risk of severe immune-related adverse events, should be considered. Immunotherapy remains a viable second/third line option, though, optimal patient selection and predictive biomarker identification are essential.

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