Extra embryonic elements in testicular tumours

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Abstract
Extra embryonic elements in germ cell tumours resemble the trophectoderm or yolk sac endoderm which are the extra embryonic membranes of the developing embryo. True chorionic (trophoblastic) differentiation with syncytiotrophoblast and cytotrophoblast, perhaps with a villous pattern, is rare and is associated with a very poor prognosis and with hCG production. Isolated syncytiotrophoblastic cells also produce hCG but are prognostically less sinister. Yolk sac elements occur in two thirds of non seminomatous germ cell tumours, and affect all age groups. Pure forms of yolk sac tumour (YST) occur but are not common except in infants. They are often associated with AFP production but AFP is not a specific marker for YST. Yolk sac tumours have a similar prognosis to malignant teratoma undifferentiated (MTU: embrvonal carcinoma).