Primary Cutaneous Epithelioid Mesenchymal Tumor With a Novel ATP2B4::GLI1 Gene Fusion

ABSTRACT

GLI1 gene alterations (rearrangement or amplification) have been found in several bone and soft tissue tumors including pericytic tumors, gastric plexiform fibromyxoma, gastroblastoma, and a various group of epithelioid tumors with regional recurrence or distant metastasis. In this article, we describe a case of primary cutaneous epithelioid mesenchymal tumor harboring hitherto not reported ATP2B4::GLI1 gene fusion. A 42-year-old man presented with a growing firm lesion on the left postauricular scalp. Microscopically, the shave biopsy specimen revealed a dermal-based nodular proliferation of relatively monotonous epithelioid cells with round to ovoid nuclei and pale eosinophilic cytoplasm, accompanied by prominent stromal vasculature. Significant cytologic atypia, necrosis, and mitotic activity were absent. The tumor cells were partially positive for CD34 and S-100 protein, but were negative for other markers, including SOX-10, keratins, and myogenic markers. An ATP2B4::GLI1 gene fusion was identified by next-generation sequencing. Array CGH was also performed, but it did not show relevant chromosomal copy number changes. Awareness of this rare cutaneous tumor, and thus, reporting of additional cases is necessary for further delineating its full clinicopathologic spectrum.

MAML2 Gene Rearrangement Occurs in Nearly All Hidradenomas: A Reappraisal in a Series of 20 Cases

ABSTRACT

Hidradenoma is a benign cutaneous adnexal neoplasm that occurs across a wide age range and at a variety of anatomic sites. Its most characteristic morphologic feature is the presence of diverse cell types including squamoid, clear, plasmacytoid, and mucinous cells. Hidradenoma is morphologically and molecularly similar to mucoepidermoid carcinoma, and both tumors are characterized by recurrent CRTC1-MAML2 cytogenetic translocations. Previous studies have suggested that approximately half of hidradenomas possess this translocation. This finding raised the question of whether translocation-negative hidradenomas might have an alternate molecular basis. Here, we sought to reevaluate the frequency of MAML2 translocation in hidradenoma in a series of 20 cases. We find that 90% show evidence of MAML2 translocation, suggesting that this genetic event is a nearly invariant feature of hidradenoma. These results inform our molecular understanding of this tumor and may be useful in challenging cases to distinguish hidradenoma from its histologic mimics.

Molecular analysis of NUT-positive poromas and porocarcinomas identifies novel break points of YAP1::NUTM1 fusions

BACKGROUND

Poromas, 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.

METHODS

13 NUT IHC-positive poroid tumors (4 poromas, 9 porocarcinomas) were identified within a 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 one read spanning YAP1-NUTM1 breakpoints 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.

CONCLUSION

While no novel NUTM1 fusion partners were identified within our cohort, twelve of thirteen 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. Additionally, 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.