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Cuticular Poroma: A Rare Poroma Variant Simulating a Malignant Neoplasm That Often Harbors YAP1::NUTM1 Fusions Similar to Their Conventional Counterparts

Publication at Faculty of Medicine in Pilsen |


Cuticular poroma is a rare variant of poroma composed of exclusively or predominantly cuticular cells, namely of large cells with ample eosinophilic cytoplasm. We report 7 cases of this rare tumor identified among 426 neoplasms diagnosed as poroma or porocarcinoma.

The patients were 4 males and 3 females, ranging in age from 18 to 88 years. All presented with a solitary asymptomatic nodule.

The location included knee (2 cases), shoulder, thigh, shin, lower arm, and neck (each 1). All lesions were surgically removed.

No evidence of disease was observed in 5 patients with available follow-up (range 12-124 months).Microscopically, all neoplasms were composed of variably sized, focally closed packed, or interconnecting nodules constituted mostly of cuticular cells. Small poroid cells were a focal feature in 5 tumors, whereas in the remaining 2 cases, poroid cells with conspicuous but still in minority.

Five neoplasms were somewhat asymmetric, with irregular outlines. Ductal differentiation and intracytoplasmic vacuoles were seen in 6 tumors.

Other features variably encountered were conspicuous intranuclear pseudoinclusions, cystic change, occasional multinucleated cells, increased mitoses, and stromal desmoplasia. Four of the 5 tumors analyzed with next-generation sequencing yielded YAP1::NUTM1 fusions.

In addition, various mutations, mostly of unknown significance were identified in one neoplasm.