Undiff. Pleomorphic Sarcoma: Microscopic

Comments:
Microscopic Features: The background in undifferentiated pleomorphic sarcomas (UPS) contains scant collagenous stroma, which is sometimes extensive. Some cases show osteoid or chondroid matrix. Depending upon the amount and appearance, such cases are more appropriately diagnosed as osteosarcoma or chondrosarcoma.

The vascular spaces in UPS are generally delicate and slit-like. They are barely discernible in this image. However, in some cases, they are dilated and acquire staghorn configuration (hemangiopericytomatous; see next image).