Snow, Justin T.

AbstractBackgroundCutaneous metastases from non‐cutaneous neuroendocrine neoplasms are rare; however, distinction from primary neuroendocrine carcinomas of the skin (Merkel cell carcinoma) guides clinical management.MethodsWe performed a retrospective review from September 1, 2010 to September 30, 2020 of the histopathologic, immunohistochemical, and clinical characteristics of metastatic neuroendocrine neoplasms to the skin from non‐cutaneous primaries.ResultsFourteen patients were identified for the study (nine males and five females; mean age of 59.5 years). Fifteen skin specimens from 14 patients were available for review. At the time of skin biopsy, a known non‐cutaneous neuroendocrine neoplasm was present in 50% of patients. Primary sites of neuroendocrine carcinoma included lung (n = 5), terminal ileum (n = 2), and one each from prostate, breast, rectum, uterus, esophagus, and sinus, with one unknown (suspected bladder malignancy). Eleven of fourteen patients are dead of disease; one was lost to follow‐up. All 15 specimens showed subcutaneous/deep dermal involvement with six involving the papillary dermis and one involving the epidermis. The tumors ranged from well to poorly differentiated. Two of fifteen specimens showed focal CK20 positivity (one metastatic uterine small cell carcinoma and one metastatic ileal carcinoid). TTF‐1 was performed in 13 specimens and was positive in six, of which two were of non‐pulmonary origin.ConclusionsWhile immunohistochemical stains, in particular CK20, CK7, and TTF‐1, are integral in the workup of confirming the origin of neuroendocrine tumors found in the skin, results vary and are often non‐specific for a single primary site. Therefore, complete radiologic imaging as well as clinical correlation should be recommended to further aid in the identification of a non‐cutaneous primary neoplasm.

AbstractBackgroundPoromas, and their malignant counterparts, porocarcinomas, harbor recurrent translocations involving YAP1‐MAML2, YAP1‐NUTM1, and infrequently WWTR1‐NUTM1; YAP1‐NUTM1 being the most common in porocarcinomas. NUT immunohistochemistry (IHC) can be used to identify NUTM1‐translocated tumors. This study sought to investigate potential novel NUTM1‐fusion partners among NUT IHC‐positive poromas and porocarcinomas.MethodsThirteen NUT IHC‐positive poroid tumors (four poromas and nine porocarcinomas) were identified within a multi‐institutional international cohort. Next‐generation sequencing (NGS) assessed for NUTM1 fusion partners.ResultsNGS detected a NUTM1 fusion in 12 of 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 one read‐spanning YAP1‐NUTM1 break point upon manual review. A NUTM1 fusion was not identified in one case; however, the sample had low RNA quality. The following fusion events were identified: YAP1 exon 4::NUTM1 exon 3 in six cases, YAP1 exon 6::NUTM1 exon 2 in one case, YAP1 exon 3::NUTM1 exon 3 in three cases, WWTR1 exon 3::NUTM1 exon 3 in one case, and YAP1 exon 8::NUTM1 exon 3 fusion in one case.ConclusionWhile no novel NUTM1 fusion partners were identified within our cohort, 12 of 13 cases had discoverable NUTM1 fusions; 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 further substantiate the utility of NUT IHC in diagnosing a subset of poroid neoplasms. In addition, two of our cases harbored fusions of YAP1 exon 6 to NUTM1 exon 3 and YAP1 exon 8 to NUTM1 exon 2, which have not been reported before in poroid neoplasms and indicate novel break points of YAP1.