A deciduoid vulvovaginal tumour that can point to germline BAP1 variants

Design

Case series with immunohistochemical and molecular profiling

Population

4 women aged 34–48 with vaginal or Bartholin region tumours

Primary outcome

Morphological, immunohistochemical and molecular features; recurrence

Effect

ER/PR diffusely positive in all; BAP1 loss with germline variant in 2 of 4; no recurrence at 8 months to 15 years

A report in the American Journal of Surgical Pathology, published on 12 October, describes four cases of a mesenchymal tumour of the vagina or Bartholin gland region in women aged 34 to 48. The tumours were 25 to 55 mm, solid and well circumscribed, made mostly of epithelioid cells with abundant glassy, granular eosinophilic cytoplasm resembling decidua, with prominent vessels and a mild lymphoid infiltrate.

All were diffusely positive for oestrogen and progesterone receptors, CD63 and vimentin. Two showed loss of BAP1 on immunohistochemistry, and both of those patients carried inactivating germline BAP1 variants. All four had copy number loss at 14q and/or 17q and alterations in MAPK pathway genes. None recurred over follow-up of 8 months to 15 years.

The authors propose it as a new entity within BAP1 tumour predisposition syndrome. The practical point for a reporting pathologist is that a hormone receptor-positive epithelioid tumour with deciduoid cytoplasm at this site warrants BAP1 immunohistochemistry, because loss raises the possibility of a germline syndrome with implications for the patient and her family.

• Consider this entity for a well-circumscribed epithelioid vulvovaginal tumour with glassy deciduoid cytoplasm and ER/PR positivity.
• Request BAP1 immunohistochemistry on such tumours.
• If BAP1 is lost, recommend genetic referral; BAP1 predisposition carries risks of uveal and cutaneous melanoma, mesothelioma and renal cancer.
• Exclude true decidual change and other epithelioid mesenchymal tumours in the differential.

Why it matters

A benign-behaving tumour may be the first sign of a germline cancer predisposition syndrome.

Don't overread it

Four cases define a pattern, not its frequency or full behaviour.

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