Ultrasound scan of the left testicle of a 29 year old man with testicular cancer. This is a seminoma, a malignant (cancerous) germ cell tumour that originates in the seminiferous tubules. It is the most common form of testicular cancer and occurs most often in men between the age of 30 to 45 years. It usually presents as a firm painless lump on a testicle. Treatment, which in 90 per cent of cases leads to a cure, is with removal of the affected testicle, a procedure known as an orchidectomy.