Vulvar yolk sac tumor diagnosed during pregnancy, with recurrence during subsequent second pregnancy

A Subset of SMARCB1 (INI-1)-deficient vulvar neoplasms express germ cell markers

AIMS

SMARCB1 (INI-1)-deficient vulvar neoplasms comprise a group of rare tumours that include epithelioid sarcoma (ES), myoepithelial carcinoma (MEC), the recently described myoepithelioma-like tumour of the vulvar region (MELTVR), and sarcomas that are difficult to classify. It has been suggested that so-called vulvar yolk sac tumours (YST) may represent morphologic variants of SMARCB1-deficient tumours; thus, we investigated the immunoreactivity of germ cell markers in SMARCB1-deficient vulvar neoplasms.

METHODS AND RESULTS

Ten SMARCB1-deficient vulvar neoplasms were stained with germ cell tumour markers (SALL4, glypican-3, OCT3/4, and AFP) and re-reviewed for morphologic features. The tumours occurred in adult females (median age 41 years) and included ES (n = 7), MELTVR (n = 2), and MEC (n = 1). All cases showed loss of SMARCB1 expression. Four cases (40%) were focally positive for SALL4 in areas with morphology of typical-appearing ES. One of these cases also showed focal staining for OCT3/4. One ES showed a transition from typical-appearing ES to YST-like morphology, with diffuse expression of SALL4 and glypican-3, and focal expression of AFP, in these latter areas. All other tested cases were negative for AFP.

CONCLUSION

Our study reveals that SALL4, glypican-3, and OCT3/4 are positive in a subset of SMARCB1-deficient vulvar neoplasms, which may pose a diagnostic challenge and result in consideration of a germ cell tumour. We also highlight a case with transition from ES to YST-like morphology, lending further support that YSTs of the vulva are somatically derived SMARCB1-deficient neoplasms and do not represent true germ-cell neoplasia.

Vulvar Yolk Sac Tumors Are Somatically Derived SMARCB1 (INI-1)-Deficient Neoplasms

So-called primary yolk sac tumors of the vulva are very rare and often have an aggressive disease course. Their molecular features have not been previously characterized. There is also a well-documented group of SMARCB1 (INI-1)-deficient vulvar neoplasms, which includes proximal-type epithelioid sarcoma and myoepithelial carcinoma. Until now, "vulvar yolk sac tumors" and SMARCB1-deficient neoplasms were considered unrelated diseases. After reviewing an index case of a vulvar yolk sac tumor with loss of SMARCB1 by immunohistochemistry, we retrospectively identified 2 additional cases diagnosed as vulvar yolk sac tumors. Patient ages were 34, 32, and 25 years old, and 2 tumors were associated with a pregnancy. All 3 cases showed morphology typical of a yolk sac tumor, and by immunohistochemistry all were positive for SALL4, glypican-3, keratins, and lacked CD34 positivity. All tumors also demonstrated loss of SMARCB1 in tumor cells. Targeted molecular profiling was performed in 2 cases and identified 2 copy deletion of SMARCB1, without genomic alterations typically seen in gonadal yolk sac tumors. In the third case, isochromosome 12p was not identified by fluorescence in situ hybridization. All 3 patients had either local recurrences or distant metastases, and 2 died of disease. One patient had progressive disease while receiving the enhancer of zeste homolog 2 inhibitor tazemetostat. Overall, these findings suggest that vulvar tumors with pure yolk sac-like morphology may represent morphologic variants of SMARCB1-deficient tumors and not veritable germ cell neoplasia. This potential reclassification may have both prognostic and treatment implications and warrants study of additional extragonadal yolk sac tumors.

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

AIMS

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.

METHODS AND RESULTS

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.

CONCLUSIONS

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.