Osteosarcoma is treated with a multimodality approach that consists of (1) neoadjuvant chemotherapy, (2) surgery, and (3) chemotherapy. The amount of chemotherapy-induced necrosis found at surgical resection is an important prognostic finding. These aggressive neoplasms spread hematogenously to the lungs. Although the prognosis has improved substantially since the advent of chemotherapy, with 5-year survival rates reaching 60% to 70% in patients without detectible metastases at initial diagnosis, the outcome for patients with metastases, recurrent disease, or secondary osteosarcoma is still poor.
Fig.21.18Fine,lacelikepatternofneoplasticboneproducedbyanaplasticmalignanttumorcellsinanosteosarcoma.Notetheabnormalmitoticfigure(arrow).
These tumors are characterized by the formation of hyaline cartilage. Benign cartilaginous tumors are much more common than malignant ones.
Osteochondroma, known clinically as exostosis, is a benign cartilage-capped tumor that is attached to the underlying skeleton by a bony stalk. About 85% are solitary. The remainder are seen as part of the multiple hereditary exostoses syndrome (see later). Solitary osteochondromas are usually first diagnosed in late adolescence and early adulthood, but multiple osteochondromas become apparent during childhood. Men are affected three times more often than women. Osteochondromas develop in bones of endochondral origin and arise from the metaphysis near the growth plate of long tubular bones, especially near the knee (
Fig. 21.19 ). They present as slow-growing masses, which can be painful if they impinge on a nerve or if the stalk is fractured. In many cases they are detected incidentally. In multiple hereditary exostoses, the underlying bones may be bowed and shortened, reflecting an associated disturbance in epiphyseal growth.
Hereditary exostoses are associated with germline loss-offunction mutations in either the EXT1 or the EXT2 gene and subsequent loss of the remaining wild-type allele in chondrocytes of the growth plate. Reduced expression of EXT1 or EXT2 also has been observed in sporadic osteochondromas. These genes encode enzymes that synthesize heparan sulfate glycosaminoglycans. The reduced or abnormal glycosaminoglycans may prevent normal diffusion of Hedgehog factors, which are local regulators of cartilage growth, thereby disrupting chondrocyte differentiation and skeletal development.
MORPHOLOGYOsteochondromasaresessileorpedunculated,andtheyrangeinsizefrom1to20cm.Thecapiscomposedofbenignhyalinecartilage(
Fig.21.20 )andiscoveredperipherallybyperichondrium.Thecartilagehastheappearanceofadisorganizedgrowthplateandundergoesendochondralossification,withthenewlymadeboneformingtheinnerportionoftheheadandstalk.Thecortexofthestalkmergeswiththecortexofthehostboneresultingincontinuitybetweenthemedullaoftheosteochondromaandthehostbone.
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Fig.21.19Thedevelopmentofanosteochondroma,beginningwithanoutgrowthfromtheepiphysealcartilage.
Fig.21.20Osteochondroma.(A)Radiographofanosteochondromaarisingfromthedistalfemur(arrow).(B)Thecartilagecaphasthehistologicappearanceofdisorganizedgrowthplate–likecartilage.