# Evaluation of PRDM10 gene rearrangement by immunohistochemistry and molecular methods in unclassifiable undifferentiated soft tissue tumors

## TL;DR

This study finds that PRDM10 gene rearrangement occurs in some undifferentiated soft tissue tumors, not just CD34-positive fibroblastic tumors, and highlights the limitations of immunohistochemistry for detection.

## Contribution

The study expands the known occurrence of PRDM10 gene rearrangement to undifferentiated pleomorphic sarcomas and compares detection methods.

## Key findings

- PRDM10 gene rearrangement was found in two undifferentiated pleomorphic sarcomas.
- Immunohistochemistry showed low sensitivity for detecting PRDM10 rearrangements.
- Fluorescence in situ hybridization is more reliable than immunohistochemistry for this detection.

## Abstract

Soft tissue sarcomas are heterogenous groups of tumors that show variable morphology as well as clinical behavior. Morphological features do not always directly reflect clinical behavior. Certain mesenchymal tumors exhibit an indolent clinical course. Among them are superficial CD34-positive fibroblastic tumors characterized by PRDM10 fusion. In our study, we aimed to detect PRDM10 gene rearrangement in superficial CD34-positive fibroblastic tumors and other pleomorphic sarcomas included in its differential diagnosis by immunohistochemistry and Fluorescence in situ hybridization. Totally, 33 cases were enrolled into this study. The results showed that two cases diagnosed as superficial CD34-positive fibroblastic tumor and two cases diagnosed as undifferentiated pleomorphic sarcoma have PRDM10 gene rearrangement. Immunohistochemically, not all rearranged tumors showed PRDM10 staining that suggests a low sensitivity of PRDM10 antibody. In conclusion, we suggested that PRDM10 gene rearrangement is not limited to superficial CD34-positive fibroblastic tumors; undifferentiated pleomorphic sarcomas may exhibit this molecular alteration and immunohistochemistry has lower sensitivity than fluorescence in situ hybridization.