Testicular cancer in a 39-year-old man. The cancer is affecting the left testicle (at right), and is a malignant spermatocytic seminoma. A seminoma is a malignant tumour (cancer) of the testis (testicle). Although this is a rare cancer, it is the most common cancer in 15 to 35- year-old men. It arises from abnormal germ cells (precursors to sperm cells) in the seminiferous tubules. Surgical removal of the affected testis (orchidectomy) is followed by radiotherapy and chemotherapy if required. For a view of this patient's genitals following surgery, see image C047/8464.