WORLD HEALTH ORGANIZATION - PATHOLOGIC CLASSIFICATION OF TESTICULAR TUMOURS

The World Health Organization classification of testicular neoplasms is most widely used scheme.
Germ Cell Tumours :
Tumours of one histologic type:
1. Seminoma
2. Spermatocytic seminoma
3. Embryonal Carcinoma
4. Yolk sac tumor (embryonal carcinoma, infantile type)
5. Polyembryoma
6. Choriocarcinoma
7. Teratoma:
a) Mature
b) Immature
c) With malignant transformation
Tumours showing more than one histologic pattern:
1. Embryonal carcinoma plus teratoma (teratocarcinoma)
2. Choriocarcinoma and any other type (specify type)
3. Other combinations (specify)
Sex Cord-Stromal Tumours:
Well-differentiated forms:
1. Leydig cell tumour
2. Sertoli cell tumour
3. Granulosa cell tumour
Mixed forms (specify) :
Incompletely differentiated forms:

Abstract: WHO classification of testicular tumors. Verh Dtsch Ges Pathol.2002;86:67-75.
Twenty years after the first edition (1977), the WHO has presented the updated version of the "Histological typing of testis tumours". The revised classification was necessary because some clinically important new entities have been described in recent years. The most important is obviously the precursor lesion of germ cell tumors, which has been called "intratubular malignant germ cells". Such atypical cells appear in the tubules adjacent to the germ cell tumors, in some few cases (6%) also in the contra lateral healthy gonad and rarely in infertile men (1%). The precursor lesion can progress to franc germ cell tumor starting probably with seminoma, which still maintain the capability of differentiation (pluripotente cells) in all other types of non-seminomatous germ cell tumors. This lesion is missed in germ cell tumors of childhood and in spermatocytic seminomas, both seem to have a histogenetic history rather different from the other germ cell in adults. The categories used in the first classification have been preserved and some new diagnoses added. Most of the new diagnoses are subtypes--called "variants"--of well known tumors. Seminoma with syncytiotrophoblastic cells is a variant which should not be confused with choriocarcinoma. Spermatocytic seminomas are perfectly benign tumors but they become a life threatening disease when combined with sarcomas (new entity). In the group of mature teratomas the "dermoid cyst" appears as a benign subtype mostly observed in children. Unfortunately, however, the old term "teratoma with malignant transformation" was changed to "teratoma with malignant areas" in the 1998 classification. This is a harmless name for an extremely dangerous tumor in which one tissue overgrows the other and gives rise to somatic type sarcomas or carcinomas. Such tumors do not respond like germ cell tumors to the usual chemotherapy. Treatment should be tailored according to that used in standard management of the respective sarcoma or carcinoma. In the comments it is mentioned that the testis carcinoid could be a part of teratoma, but the diagnosis is listed in the group of "miscellaneous" tumors together with tumors of ovarian epithelial type. This is a very questionable decision because the normal testis does not contain neuroendocrine cells from which carcinoids would have to be able to develop. Teratomas, however, show plenty of them producing all kinds of typical hormones. "Large cell calcifying Sertoli cell tumour" has been recently described and can be sporadic or inherited. This morphologically peculiar tumor can be part of the Swiss syndrome also called Carney's complex. The patients have cardiac myxomas, spotty skin pigmentation, hormone active nodular hyperplasia of the adrenals and soft tissue myxomas. The newly appearing "mixed germ cell--sex cord/gonadal stromal tumours, unclassified" has a histology similar to the well known gonadoblastomas. In contrast to gonadoblastoma, however, these tumors occur in testes of genotypic and phenotypic normal males. From the practical, diagnostic point of view the new classification does not contain dramatic changes. For the therapy of germ cell tumor an assessment of risk factors found by the pathologists is extremely important. The most important independent predictors of relapse are tumor invasion of blood or lymph-vessels, absence of yolk sac elements and the presence of an embryonal carcinoma component. In the absence of such predictors a surveillance policy allows some patients to forgo chemotherapy.