Fibroepithelial Stromal Polyp of the Vulvovaginal Region as Part of the RB1 Family of Tumors: Friend or Foe?

Fibroepithelial stromal polyps (FSPs) are benign mesenchymal lesions occurring in the vulvovaginal region. Following the identification of loss of Retinoblastoma 1 (RB1) on immunohistochemical staining in routine practice, we stained a series of FSPs and performed additional fluorescence in situ hybridization (FISH) and copy number variation (CNV) sequencing to detect losses/deletions in the Retinoblastoma transcriptional corepressor 1 (RB1) gene. Fifteen FSP cases were stained for RB1, and subsequently, 9 cases were examined by FISH to detect a loss of RB1 (13q). Next, CNV sequencing was performed to assess genomic alterations. The mean age of the patients was 50 years. Loss of RB1 expression on immunohistochemistry was seen in 13 cases, and heterogeneous RB1 staining in the remaining 2 cases. FISH showed deletion of RB1 in all of the cases. CNV sequencing failed in almost all cases due to a low tumor content. Based on our findings, we hypothesize that FSPs are part of a spectrum of genetically related lesions, namely the 13q/RB1 family of tumors (which includes pleomorphic fibromas and spindle cell/pleomorphic lipomas). Due to the clinical, morphologic, and molecular overlap, we suggest that FSPs are pleomorphic fibromas occurring in the specialized stroma of the genital region.