A new classification of germ cell tumours of the testis.

The partially conflicting British and WHO classifications of testicular tumours are confusing and fail to give due prominence to their histogenesis from carcinoma in situ (CIS). Spermatocytic seminoma does not originate from CIS and should be renamed 'spermatocytoma'. All other germ cell tumours are gonocytomas arising from CIS cells which have many of the characteristics of the gonocytes of the early embryo and fetus. Gonocytomas are subdivided into seminoma, if they retain their gonocyte characteristics, or teratogenic gonocytoma if the tumour stem cell has differentiation potential. A new category of anaplastic germ cell tumour is intermediate between seminoma and teratogenic gonocytoma. The teratogenic gonocytoma is an epiblastoma if no differentiation is manifest, but may differentiate along embryonic lines into teratoma or may show extraembryonic differentiation towards yolk sac tumour or choriocarcinoma. The new classification uses unambiguous terminology and is midway between the British and WHO classifications. Those familiar with either of these classifications should have no difficulty in adapting to the new proposals, and the new classification should help others to acquire a better understanding of the biology and pathology of testicular germ cell tumours.