# Acral Mesenchymal Spindle Cell Neoplasm With a Novel HMGA2::NCOA2 Fusion

## TL;DR

This paper reports the first case of a rare skin tumor in a young woman with a new genetic fusion, HMGA2::NCOA2, highlighting the importance of genomic testing in diagnosing unusual tumors.

## Contribution

The paper presents the first documented case of an HMGA2::NCOA2 fusion in an acral mesenchymal tumor.

## Key findings

- The tumor had a novel HMGA2::NCOA2 fusion identified through next-generation sequencing.
- The tumor showed benign features but was surgically removed due to the fusion's unpredictable behavior.
- The case underscores the need for further research and clinical follow-up on this genetic fusion.

## Abstract

Molecular profiling has revolutionized the field of soft tissue pathology, enhancing diagnostic precision and treatment strategies. The integration of molecular analysis and immunohistochemistry has been crucial for classifying diagnostically challenging acral mesenchymal neoplasms. Herein, we report the first documented case of an acral mesenchymal spindle cell neoplasm harboring an HMGA2::NCOA2 fusion. The neoplasm presented as a slow‐growing verrucous papule on the right thumb of an 18‐year‐old female. Histological examination revealed spindled cells of varying cellularity with intervening sclerotic collagen and dilated vasculature. The cells had patchy S100 and focal GLUT‐1 reactivity but were negative for CD34, EMA, Sox‐10, Pan‐TRK, p63, CKAE1/3, MUC4, ALK, Factor 13A, actin, desmin, and ERG. Given the unusual morphology and non‐diagnostic immunohistochemical profile, the specimen was sent for additional molecular profiling. Next‐generation sequencing revealed a novel in‐frame HMGA2::NCOA2 fusion. The tumor was likely benign, with 4 mitoses per 10 high‐powered fields (HPF), but was excised due to the unpredictable behavior of the fusion. As the first known case to date with this fusion, these findings contribute to the emerging research on genomic testing in acral soft tissue tumors. Additional cases and longer clinical follow‐up are needed to better characterize the novel HMGA2::NCOA2 fusion.