Epithelioid osteosarcoma, light micrograph

Epithelioid osteosarcoma, light micrograph. Osteosarcoma is a malignant neoplasm in which the tumour cells produce immature bone or osteoid. Based on the morphology, the most common types of osteosarcomas are osteoblastic, chondroblastic, and fibroblastic. Less common subtypes include epithelioid, giant cell-rich, clear cell, and telangiectatic osteosarcomas. This is an epithelioid osteosarcoma. Epithelioid osteosarcoma consists of a predominant population of poorly-differentiated epithelioid cells mimicking a carcinoma (upper right). 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. Haematoxylin and eosin stain., by WEBPATHOLOGY/SCIENCE PHOTO LIBRARY