Cause:Neoplasia from suppressor gene inactivation
Pathophys:Osteoid, lytic, and sclerotic forms may all coexist, or 1 may predominate. Bloodborne metastases usually, lymphatic spread rare; may involve joints in persons with mature epiphyses; originate in metaphysis; and spread via haversian system; double q 34 days
Incidence in males twice that in females; 900/yr in US; more common under age 20 yr. Associated with Paget’s, radiation exposure (takes 12+ yr) esp in children rx’d for Ewing’s and retinoblastoma with chemotherapy and radiation (Nejm 1987;317:588). Not associated with trauma, though trauma often leads to discovery of the tumor
20-40% relapse, mostly within 1 yr; all that will relapse do so within 2 yr; 80-90% relapse in the 20% with gross metastases on presentation; relapse correlates w p-glycoprotein presence, which is assoc w drug resistance (Nejm 1995;333:1380)
Lab:
Path:Osteoid, lytic, and/or sclerotic osteoblasts seen in wild formations, no longer lined up along bony trabeculations (contrast myositis ossificans)
Xray: “Ray” formation subperiosteally in sclerotic form; calcified area expands constantly in time