Somatostatin receptor expression in parathyroid neoplasms

INTRODUCTION: Parathyroid carcinoma represents a rare cause of primary hyperparathyroidism. Distinguishing carcinoma from the benign tumors underlying primary hyperparathyroidism remains challenging. The diagnostic criteria for parathyroid carcinoma are local and/or metastatic spreading. Atypical parathyroid adenomas share other histological features with carcinomas but lack invasive growth. Somatostatin receptors are commonly expressed in different neuroendocrine tumors, but whether this also holds for parathyroid tumors remains unknown. Our aim is to examine the immunohistochemical expression of somatostatin receptor 1-5 in parathyroid typical adenomas, atypical adenomas, and carcinomas. METHODS: We used a tissue microarray construct from a nationwide cohort of parathyroid carcinomas (n = 32), age- and gender-matched typical parathyroid adenomas (n = 72), and atypical parathyroid adenomas (n = 27) for immunohistochemistry of somatostatin receptor subtypes 1-5. We separately assessed cytoplasmic, membrane, and nuclear expression and also investigated the associations with histological, biochemical, and clinical characteristics. RESULTS: All parathyroid tumor subgroups expressed somatostatin receptors, although membrane expression appeared negligible. Except for somatostatin receptor 1, expression patterns differed between the three tumor types. Adenomas exhibited the weakest and carcinomas the strongest expression of somatostatin receptor 2, 3, 4 and 5. We observed the largest difference for cytoplasmic somatostatin receptor 5 expression. CONCLUSIONS: Parathyroid adenomas, atypical adenomas, and carcinomas all express somatostatin receptor subtypes 1-5. Somatostatin receptor 5 may serve as a potential tumor marker for malignancy. Studies exploring the role of somatostatin receptor imaging and receptor-specific therapies in patients with parathyroid carcinomas are needed.