Yolk sac tumours of the female genital tract in older adults derive commonly from somatic epithelial neoplasms: somatically derived yolk sac tumours

To report 18 yolk sac tumours (YSTs) of the female genital tract (17 ovary, one uterus) in patients aged 40 years or over, most arising from a somatic epithelial neoplasm.Six patients had pure YST, two were associated with immature teratoma (one with an endometrioid adenocarcinoma) and in 11 there was an epithelial neoplasm comprising high-grade serous carcinoma (HGSC) (n = 5), clear cell carcinoma (n = 1), borderline clear cell adenofibroma (n = 1), endometrioid adenocarcinoma (n = 2), serous tubal intra-epithelial carcinoma (n = 1) and large-cell neuroendocrine carcinoma (n = 1). In one case of pure YST, there was an ipsilateral endometriotic cyst but no other neoplastic component. In two cases, the YST was a hepatoid variant and in most of the others it exhibited predominantly glandular morphology, closely mimicking an epithelial neoplasm.Pathologists should be aware of the association between YST and an epithelial neoplasm, the former probably arising from the latter through a process of neometaplasia/retrodifferentiation. Those rare gynaecological pure glandular YSTs in adults may arise secondary to total overgrowth of an epithelial neoplasm. Pathologists need a high index of suspicion to diagnose the YST component, as the morphology is characteristically of a glandular variant with marked morphological overlap with adenocarcinomas. There is also often significant immunophenotypical overlap with epithelial neoplasms, as the YST component may be positive with epithelial membrane antigen (EMA), BerEP4 and cytokeratin 7 (CK7), as well as YST markers. We propose the term 'somatically derived YSTs' for these neoplasms and suggest unification of the terminology between different sites where such neoplasms occur.