Well-differentiated intramedullary osteosarcoma: A report of five cases

Well-differentiated intraosseous osteosarcoma (WDIOS) is a rare tumor and histologically similar to parosteal osteosarcoma. This study reports the clinicopathological features of five patients with WDIOS tumor seen at the Instituto Nacional de Cancerologia in Mexico City. The patients' ages ranged from 29 to 42 years with a median age of 32 years. Four of the five patients presented with pain and a mass that had been present for more than 3 years prior to the diagnosis. Radiologically, four of the lesions were present in the long bones and showed a predominantly trabeculated appearance with some small ill-defined lytic areas. The bony sclerosis was more prominent within the medullary cavity than in the soft tissue extension. The majority of the tumors were large, averaging 21 cm in size. Histologically, the tumors were characterized by spindle cells with areas of cytologic atypia and presence of mature bone formation. In two patients a high-grade sarcoma component was found in addition to WDIOS component: in both patients the high-grade sarcoma component was identified in the amputation specimens, and in one of these it was also recognized in the pulmonary metastasis. This study demonstrated that WDIOS is a slow-growing malignant neoplasm that may show a histologic progression to dedifferentiation (dedifferentiated osteosarcoma) and an aggressive behavior with distant metastasis.