SEMINOMAS OF THE CANINE TESTIS - COUNTERPART OF SPERMATOCYTIC SEMINOMA OF MEN

BACKGROUND: Dogs develop germ cell tumors of the testis at a relativel y high rate. It is not known to what degree these tumors resemble vari ous human testicular neoplasms. EXPERIMENTAL DESIGN: The epidemiology and morphology of a series of spontaneous canine testicular tumors, co llected between 1985 and 1991, was analyzed, and compared with human t esticular germ cell tumors. DNA content analysis of representative sam ples was performed using flow cytometry and image cytometry. Eight hum an spermatocytic seminomas were studied in parallel. RESULTS: All cani ne tumors had the histopathologic features reported as typical for dog testis seminomas. These tumors could show both an intratubular and an invasive component. Most of them were pure (78%), while they could be combined with a Leydig cell tumor, a Sertoli cell tumor, or both. No somatic, placental or yolk sec cells were identified, and there was no carcinoma in situ (CIS). A bimodal age distribution, with a peak arou nd 1 year of age and between 4 and 16 years of age, was found for ail pure and mixed testicular tumors, except for those composed of a Leydi g cell and a seminoma component. These tumors were all present in dogs older than 7 years, being significantly more older (p < 0.01) than do gs with a pure tumor of either type. All Sertoli cell and Leydig cell tumors were diploid. No consistent peritriploid DNA content, character istic of human testicular germ cell tumors, was found for canine semin omas, which most often had a diploid DNA content. Human spermatocytic seminomas always contained diploid tumor cells, and showed a relativel y low number of high ploidy cells, comparable to canine seminomas of t he testis. CONCLUSIONS: The so-called seminomas of the testis are tumo rs of old age. Histologically, these tumors are composed of a single c ell type with some variation without evidence of differentiation. It i s proposed that canine seminoma correspond to human spermatocytic semi nomas. It is thought that the Leydig elements in these tumors represen t a reactive change rather than biphasic differentiation of a single s tem cell capable of germinal and sex-cord cell development.