Clues to the appropriate malignant diagnosis include a more aggressive, infiltrative lesion on imaging studies, and the presence of nuclear atypia, atypical mitoses, and/or
malignant osteoid production on histologic examination.
There is abundant cartilage with focal endochondral ossification and trabeculae bone formation without
malignant osteoid formation.
Osteosarcoma is a malignant primary tumor of bone consisting of malignant stroma with evidence of
malignant osteoid, bone and cartilage formation (Spjut et al., 1971).
Presence of
malignant osteoid showing variable mineralization interspersed among the tumor cells.
In non-productive osteoblastic osteosarcomas, areas of
malignant osteoid tissue might be very difficult to found (5,7).
The diagnosis of cutaneous osteosarcoma is made on the basis of the histologic Finding of disorderly dermal deposition of
malignant osteoid and exclusion of a bony primary osteosarcoma and/or metastases.
Moreover, the regularly spaced spicules of woven bone seen in FD are not present in osteosarcoma, where
malignant osteoid is often deposited in broader and irregular trabeculae.