Abstract

Background: Poromas, and their rare malignant counterparts, porocarcinomas, are shown to harbor recurrent translocations involving YAP1-MAML2, YAP1-NUTM1, and rarely WWTR1-NUTM1, YAP1-NUTM1 being the most common in porocarcinomas. NUT immunohistochemistry (IHC) is widely used to identify NUTM1-translocated tumors. We sought to find novel NUTM1-fusion partners among our NUT IHC-positive poromas and porocarcinomas. Methods: 13 NUT IHC-positive poroid tumors (4 poromas, 9 porocarcinomas) were identified within our multi-institutional international cohort. Next Generation Sequencing (NGS) assessed for NUTM1 fusion partners. Results: NGS detected a NUTM1 fusion in 12/13 cases: YAP1-NUTM1 (11/12 cases) and WWTR1-NUTM1 (1/12 cases). Two of the cases (2/12) with NUTM1 fusion were not called by the NGS algorithm but had at least 1 read spanning YAP1-NUTM1 breakpoints upon manual review. The remaining case had no evidence of a NUTM1 fusion, however, this sample had low RNA quality. Conclusion: No novel NUTM1 fusion partners were identified within our cohort. Twelve of 13 cases had a NUTM1 fusion; YAP1-NUTM1 fusion was detected in 11 cases (92%) and WWTR1-NUTM1 in 1 case (8%). These data corroborate findings from other recent investigations and underscore the utility of NUT IHC in diagnosing a subset of poroid neoplasms.

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