PTHrP-mediated hypercalcemia in metastatic adrenocortical carcinoma mimicking pheochromocytoma: a diagnostic challenge.

Humoral hypercalcemia of malignancy is a paraneoplastic syndrome mediated by parathyroid hormone-related peptide (PTHrP). Adrenal masses may present a diagnostic challenge when clinical, biochemical, and imaging findings overlap with endocrine tumors such as pheochromocytoma. We report an 80-year-old man presenting with severe hypercalcemia, normal phosphate levels, elevated PTHrP, and suppressed intact parathyroid hormone. Imaging revealed an 8.8 cm heterogeneous left adrenal mass with hepatic and osseous lesions along with enlarged preauricular lymph nodes, suggestive of metastatic disease. Discordant catecholamine testing raised concern for pheochromocytoma; however, biopsy confirmed adrenocortical carcinoma. This case highlights the importance of integrating biochemical, radiological, and histopathological data in evaluating adrenal masses with atypical presentations.