Adnexal skin tumors are diagnostically challenging with few known molecular signatures. Recently, however, YAP1âMAML2 and YAP1âNUTM1 fusions were identified in poroid adnexal skin tumors.
Herein, we subjected eight poroid adnexal skin tumors (three poromas and five porocarcinomas) to fusion gene analysis by whole transcriptome sequencing and nextâgeneration DNA sequencing analysis.
YAP1 fusions were identified in six cases. YAP1âNUTM1 fusions were identified in two poromas and three porocarcinomas. A single case of porocarcinoma harbored a YAP1âMAML2 fusion. Two cases were negative for gene fusion. All cases that harbored YAP1âNUTM1 fusions showed nuclear protein in testis (NUT) expression by immunohistochemistry, with NUT being negative in the YAP1âMAML2âpositive case. In this case series, we provide a detailed histopathologic description of six YAP1âfused poroid skin tumors, which we show harbor reproducible histopathologic features, to include broad, bulbous tumor tongues with admixtures of basaloid, poroid cells punctuated by squamatized cuticles and ductules, with uniform tumor nuclei featuring frequent grooves and pseudonuclear inclusions.
Awareness of the characteristic histopathologic features of YAP1âfused poroid adnexal skin tumor is a step toward a more reproducible classification of adnexal skin tumors as well as a step toward targeted therapy for metastatic and/or unresectable examples of this poroid group of neoplasms.