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. [ABSTRACT FROM AUTHOR]