Testicular cancer. Light micrograph of tissue from a testicle in the case of a teratoma, a malignant tumour that arises from germ cells, precursors to sperm cells. More specifically, this tumour is a choriocarcinoma (malignant teratoma trophoblastic, MTT), a type of teratoma that has a bad prognosis. The cells (nuclei stained dark pink) are seen in a disrupted arrangement that is typical of cancers. Treatment is by surgical removal of the testis.