# CD34‐Positive Acral Chondromyxoid Mesenchymal Neoplasm Harboring a Novel TCF4::ERG Fusion

## TL;DR

A new type of tumor in a young woman's finger was identified through a unique genetic fusion and specific cell markers.

## Contribution

Identification of a novel TCF4::ERG fusion in a rare acral mesenchymal neoplasm with CD34 positivity.

## Key findings

- The tumor exhibited a novel in-frame TCF4::ERG fusion in a 26-year-old female.
- CD34, ERG, and focal p63 were expressed in tumor cells.
- No metastasis or recurrence was observed after 3 months of follow-up.

## Abstract

Molecular testing has significantly transformed the field of anatomic pathology over the past several decades. Despite these advances, acral mesenchymal neoplasms remain diagnostically challenging, requiring careful integration of clinical presentation, histologic features, and molecular findings for accurate classification. Herein, we present a case of an acral chondromyxoid mesenchymal neoplasm harboring a novel in‐frame TCF4::ERG fusion involving the right index finger of a 26‐year‐old female. Morphologically, this tumor consisted of nests and sheets of monotonous small round‐to‐ovoid cells embedded in a background of chondromyxoid stroma and hyalinized collagen. The tumor cells were diffusely CD34, ERG, and focally p63 reactive, while S100 protein, cytokeratin AE1/AE3, Pan‐TRK, ALK, smooth muscle actin, and desmin were negative. Albeit short follow‐up (3 months), the patient continues to do well without evidence of metastasis or local recurrence.