Testicular cancer. Light micrograph of a section through a seminoma (down left) of the testis. A seminoma is a malignant (cancerous) tumour (neoplasm) that appears as a swelling, which is often painless. The tumour consists of sheets of uniform, tightly packed, polygonal cells with large round nuclei. The cells are divided into clumps by fine fibrous divides (septa), in which there are a type of white blood cells (lymphocytes). Treatment requires the surgical removal of the testis (orchidectomy). Anticancer drugs and radiotherapy are used to control the spread of tumour cells. Magnification unknown.