Testis tumors can arise from several different cells within the testicle. The most common (and aggressive) type of testis tumor are germ cell tumors. Germ cell tumors may be either seminomas (the most common germ cell tumor) or non-seminomatous tumors (including embryonal cell cancers, choriocarcinomas and teratomas).

Other testis tumors are interstitial tumors or secondary cancers (tumors that arise from another organ and have spread to the testis.)