Osteosarcoma- Accounts for 20% of 1° bone cancers.- Peak incidence of 1° tumor in males < 20 years.- Less common in elderly- Usually 2° to predisposing factors, such as Paget disease of bone, bone infarcts, radiation, familial retinoblastoma, Li-Fraumeni syndrome.- Metaphysis of long bones (often in knee region).- Pleomorphic osteoid-producing cells (malignant osteoblasts).- Presents as painful enlarging mass or pathologic fractures.- Codman triangle (from elevation of periosteum) or sunburst pattern on x-ray. - Aggressive. 1° usually responsive to treatment (surgery, chemotherapy), poor prognosis for 2°.

Chondrosarcoma- Medulla of pelvis and central skeleton.- Tumor of malignant chondrocytes.

Ewing sarcoma- Most common in Caucasians. Generally boys < 15 years old.- Diaphysis of long bones (especially femur), pelvic flat bones.- Anaplastic small blue cells of neuroectodermal origin (resemble lymphocytes).- Differentiate from conditions with similar morphology (eg, lymphoma, chronic osteomyelitis) by testing for t(11;22) (fusion protein EWS-FLI1).- “Onion skin” periosteal reaction in bone.- Aggressive with early metastases, but responsive to chemotherapy.