Invasive Acantholytic Extramammary Paget's Disease of the Vulva With Mammary Carcinoma-Like Differentiation and MMR Loss: Report of an Unusual Case and Its Clinical Mimics.

BACKGROUND: Paget's disease (EMPD) of the vulva primarily affects postmenopausal women and can present significant challenges in early clinical detection.Case Presentation: We report an exceedingly rare case of invasive acantholytic extramammary Paget's disease in a 78-year-old female patient. After biopsy-proven carcinoma, a radical hemivulvectomy of the left vulva was performed, which revealed an invasive adenocarcinoma, most consistent with primary extramammary Paget's carcinoma. Histologic examination demonstrated a unique morphology, featuring an in-situ component with suprabasal intraepidermal acantholysis and an invasive component with various morphologies, including basaloid, skin adnexal-like, focal squamoid, and mammary-like differentiation, resembling ductal carcinoma in situ (DCIS) with comedonecrosis and invasive ductal carcinoma. This varied morphology has not been described before. Interestingly, the tumor shows loss of MMR protein (MSH2, MSH6).

CONCLUSION: In the literature, acantholytic Paget's disease and acantholytic anaplastic Paget's disease have been used interchangeably. While anaplastic Paget's disease has been reported in the mammary and extramammary sites (scrotum, esophagus), involvement of the vulva has been reported only once in the literature. However, the current case is the first documented loss of MMR. Both cases presented with invasive disease ranging in depth from 3-5 mm, and positive lymph nodes emphasizing on the urgent need to further explore prognostic factors of this rare entity and to differentiate it from other acantholytic lesions, such as squamous cell carcinoma in situ and other acantholytic dermatoses.