Differential expression of the PTEN tumor suppressor protein in fetal and adult neuroendocrine tissues and tumors: progressive loss of PTEN expression in poorly differentiated neuroendocrine neoplasms.

Genetic alteration and loss of expression of tumor suppressor gene PTEN has been found in carcinomas of the breast, prostate, and endometrium, as well as in gliomas. PTEN expression in neural crest/neuroendocrine (NC/NE) tissues and in neoplasms has not been reported. This study examines PTEN expression in embryonal, fetal, and adult tissues by immunohistochemistry. The authors found high PTEN expression in embryonal, fetal, and adult NC/NE tissues. The authors also study the PTEN expression in NC/NE neoplasms (N = 37), including 5 melanocytic nevi, 2 melanomas, 9 carcinoids, 2 moderately differentiated neuroendocrine carcinomas, 13 poorly differentiated neuroendocrine carcinomas, 2 paragangliomas, 2 pheochromocytomas, 2 medullary thyroid carcinomas, and 1 neuroblastoma. All carcinoid tumors and melanocytic nevi showed moderate or strong immunostaining for PTEN. In contrast, the majority of poorly differentiated neuroendocrine carcinomas (7 of 13) were negative for PTEN (54%); the remainder showed diminished reactivity. The two melanomas studied were also negative for PTEN immunostaining. The paragangliomas, pheochromocytomas, medullary thyroid carcinomas, and neuroblastoma all showed a strong PTEN stain. The authors postulate that PTEN is a differentiation marker for NC/NE tissue and tumors and that loss of PTEN expression may represent an important step in the progression of NE tumors.