Primary malignant bone tumors are rare. In one large series they constituted 0.2% of all neoplasms . In the year 2000, the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) program estimated 1,220,000 new cancer cases in the USA . Of these patients, 20-85% may develop bone metastases [3, 4]. During the same period it was estimated there would be 1,400 sarcomas of bone . In the UK, there were 527 new cases of primary bone cancer in 1999, with a rate of eight per million of the female population and 10 per million for the male population . Despite their relative rarity, or perhaps because of it, radiologists need to be familiar with these lesions, which can mimic or be mimicked by benign and non-neo-plastic reactive lesions, so that imaging beyond the radiograph and biopsy is performed on a logical and knowledgeable basis. The spectrum and breadth of primary bone tumors is extensive, as outlined by the 2002 tables of the World Health Organization . (WHO) and the American Joint Committee on Cancer (AJCC) . The relative frequencies of bone sarcomas according to histological type, sex, and race are shown in Table 1 . No classification system, however, is so allencompassing as to include traumatic reactive and infective lesions, all of which have to be considered by the radiologist when faced with a seemingly neoplastic lesion. Primary bone tumors as a group are bimodal, the first peak occurring during the second decade of life and the second peak in patients older than 60. Osteosarcoma, the most common non-hematological primary malignancy of bone, occurs predominantly in individuals younger than age 20, and in 80% of these patients the tumor is found in a long bone of the extremity. The predilection for the appendicular skeleton tends to decrease with age, and in patients older than 50, osteosarcoma accounts for 50% of extremity lesions . Chondrosarcomas show a gradual increase in incidence rates up to the age of 50. Half of chondrosarcomas occur in the long bones; other major sites are the pelvis and ribs. Ewing's sarcoma is similar to osteosarcoma in its age incidence and affinity for the long bones but, unlike osteosarcoma, it occurs almost exclusively in the white population (Table 1). Other selective primary tumors will be discussed under separate headings. The modality that has been introduced to the realm of orthopedic oncology since the previous edition of this volume is positron emission tomography (PET). Elevated 18-fluoro-2-deoxyglucose (18-FDG) accumulation has been demonstrated in a variety of malignant tissues, including sarcomas, and this information can be used to augment the information obtained from conventional imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) (Table presented).
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