Undiff. Pleomorphic Sarcoma : Introduction

Comments:
Introduction (continued from previous image): Undifferentiated pleomorphic sarcoma (UPS) shows no identifiable line of differentiation with immunohistochemistry. It remains a diagnosis of exclusion. There is no agreement on the definitional criteria for UPS as well as the extent to which pleomorphic sarcomas should be worked up with ancillary studies. By electron microscopy, the tumor cells have fibroblastic/myofibroblastic features.

When faced with a high-grade pleomorphic sarcoma, a panel of immunohistochemical markers is often used, including keratins, p63, p40, S-100 protein, melanocytic markers (HMB45, melan-A), muscle markers (SMA, desmin, MyoD1, myogenin), CD30, and ALK1. The selection of specific markers is guided by tumor morphology.

The distinction of UPS from its mimics is clinically important. Pleomorphic sarcomas with myogenic differentiation are more aggressive than those without myogenic differentiation. Dedifferentiated retroperitoneal liposarcoma (which often presents as inflammatory MFH) has a more indolent course than de novo pleomorphic sarcoma.