Testicular cancer. Cross-section through a gross specimen of a testicle with a teratoma, a malignant (cancerous) tumour arising from the germ (sex) cells. Cystic spaces (dark brown) are seen within the testicle. These areas of solid tissue have replaced lobules that are normally filled with seminiferous tubules. Because germ cells are pluripotent, that is they can differentiate into any cell type, teratomas contain a mixture of tissues. Hair and teeth may grow in the tumour. Treatment is with chemotherapy or removal of the testicle.