Epithelioid Osteosarcoma

Epithelioid osteosarcoma consists of a predominant population of poorly-differentiated epithelioid cells mimicking a carcinoma (upper right in this image). The presence of conventional areas with osteoid production (lower left) points to the correct diagnosis. However, some epithelioid osteosarcomas have greater resemblance to carcinoma and show little or no osteoid production. The tumor cells are round or polygonal with vesicular nuclei containing one or more prominent nucleoli. They may appear cohesive and even show gland-like areas, rosettes, or papillary configuration. When face with a poorly-differentiated carcinoma in the bones of a young patient, the possibility of epithelioid osteosarcoma should always be considered.