Question
Pathology of Seminoma testis
Answer
Seminoma is the most common germ cell tumour of the testis, arising from germ cell neoplasia in situ (GCNIS), typically affecting men in the 3rd–4th decades.
Gross: Well-circumscribed, homogeneous, grey-white to tan, lobulated mass replacing testicular parenchyma; typically does not extend through the tunica albuginea (unlike many non-seminomatous tumours), and lacks the haemorrhage/necrosis characteristic of mixed germ cell tumours.
Microscopy: Sheets and nests of large, uniform, polygonal cells with clear/glycogen-rich cytoplasm and centrally placed round nuclei with prominent nucleoli, divided by fibrous septa infiltrated by lymphocytes (and occasionally non-caseating granulomas).
Immunohistochemistry: Positive for PLAP, OCT3/4, and CD117 (c-KIT); negative for AFP (helps distinguish from yolk sac tumour and embryonal carcinoma, and confirms pure seminoma when negative).
Behaviour: Malignant but exquisitely radiosensitive and chemosensitive, spreading primarily via lymphatics (retroperitoneal/para-aortic nodes) before haematogenous spread. Excellent prognosis (>95% cure rate) even with metastatic disease, given the tumour’s marked treatment sensitivity. Serum β-hCG may be mildly elevated if syncytiotrophoblastic giant cells are present, but AFP is not elevated in pure seminoma.