OBJECTIVETo study the clinicopathological characteristics, immunohistochemical features and histogenesis of primary testicular carcinoid tumor and its differential diagnosis.

METHODSLight microscopy and immunohistochemical stains were performed in 4 cases of primary testicular carcinoid tumor.

RESULTSThe patients sought care for scrotum mass presented from 2 to 36 years, 2 cases accompanied with tender swelling of the testis. The tumors were described as nodular, yellowish-gray in color, 3.0-4.0 cm in the greatest dimensions, and well circumscribed, focal necrosis seen in 1 case. Histologically, they showed insular and trabecular patterns separated by fine fibrous bands. The tumor cells were round or polygonal with regular monomorphic nuclei, stippling chromatin and eosinophilic granular cytoplasm. There were rosette-like and tubuloglandular patterns with eosinophilic secretion in the cavity. Immunohistochemical staining for synaptophysin, chromogranin A, NSE and cytokeratin showed diffusely positive expression in the tumor cells.

CONCLUSIONPrimary testicular carcinoid tumor is extremely rare with good prognosis and its histogenesis remains controversial. Diagnostically it has to be differentiated from seminoma, metastatic carcinoid tumor, Sertoli cell tumor and granulosa cell tumor.