Seminomas are the most common malignant germ cell tumours of the testis. It is demographically more common in Caucasians, with mean age groups of 40-50 years. Some known risk factors include cryptorchidism in both affected and contralateral testis, infertility and Klinefelter syndrome. The majority of these tumours are detected at stage 1, and present clinically as a painless testicular mass.

Grossly they appear as well-demarcated single or multinodular grey-white masses with minimal necrosis. Histology shows uniform sheets of large sharply demarcated polygonal cells with clear cytoplasm, large central vesicular nuclei, and prominent nucleoli. These tumor sheets are poorly defined by fine fibrous septa containing plasma cells, histiocytes, lymphocytes and granulomatous inflammation. There are rare mitotic figures.

Immunohistochemically they demonstrate nuclear positivity for OCT3/4, and SALL4, membranous and cytoplasmic staining for PLAP, D2-40, AND CD117. The tumour stains negatively for AFP, hCG, and CD30. Differential diagnosis includes other testicular tumours. Treatment includes orchiectomy along with radiation or chemotherapy depending on the stage. Seminomas confined to the testis have a high curable rate of up to >95%.