MONDO_0003001 (seminoma) is a radiosensitive malignant germ cell tumor found in the testis (especially undescended), and extragonadal sites (anterior mediastinum and pineal gland). It is characterized by the presence of uniform cells with clear or dense cytoplasm which contains glycogen, and by a large nucleus which contains one or more nucleoli. The neoplastic germ cells form aggregates separated by fibrous septa. The fibrous septa contain chronic inflammatory cells, mainly lymphocytes. Also known as: seminoma, malignant, seminoma, pure.