[Parosteal osteosarcoma (POS). Clinical and therapeutic aspects]

Parosteal osteosarcoma is a malignant bone-forming tumor, which is characterized by its superficial origin and its high structural differentiation. Because of the radiological and histological variability, finding the right diagnosis is a great challenge for physicians, radiologists, and pathologists, especially at the time of primary manifestation. Usually there is a low-grade malignancy. Often a benign tumor is imitated so that finding the correct diagnosis is indispensable. Wide resection with sufficient margin is the adequate therapy. High-grade parosteal osteosarcoma needs adjuvant chemotherapy. Our own experience with secondary dedifferentiation and the possibility of primary undergrading shows that regarding diagnostics, operative therapy, and follow-up parosteal osteosarcoma should be treated like conventional osteosarcoma.