OBJECTIVETo investigate the clinicopathologic characteristics, diagnosis, differential diagnosis and treatment of primary neuroendocrine tumor (NET) of the testis.

METHODSUsing light microscopy and immunohistochemistry, we studied 7 cases of primary NET of the testis, reviewed relevant literature, and analyzed the clinical manifestations, histomorphologic and immunohistochemical characteristics, treatment and prognosis of the tumor.

RESULTSThe 7 male patients, at the mean age of 40.6 years, all presented with testicular painless masses, none accompanied with carcinoid syndrome. Histologically, the uniform tumor cells were arranged in trabecular, island, solid and/or flake structures and locally in a tubulo glandular pattern, round and polygonal in shape, with a small amount of lipid vacuoles in the eosinophilic cytoplasm. The cells had round nuclei with fine chromatin and rarely identified mitosis. Immunohistochemical staining showed that the tumor cells were positive for Syn, CgA, NSE and CK, with a Ki-67 positive rate of < 2%.

CONCLUSIONPrimary NET of the testis is a rare and low-grade malignancy. Early diagnosis and surgical resection are essential for good prognosis. Immunohistochemistry helps its diagnosis and differential diagnosis from other metastatic neuroendocrine carcinoma, teratomas with carcinoid, seminoma, and Sertoli cell tumor.