International variations in the incidence of childhood bone tumours.

Bone cancers comprise about 5% of childhood neoplasms. Osteosarcoma, the most common sub-type, shows a somewhat irregular geographic pattern of incidence, with low rates in some Asian (Indian, Japanese, Chinese) and Latin American populations. Incidence is similar in the sexes and rises steeply with age, accompanied by an increasing proportion of tumours localized in the long bones of the legs. Rates in the USA are higher in blacks than in whites, as a result of a higher incidence at ages 10 to 14 and of tumours of the leg bones. The descriptive epidemiology is consistent with early observations linking risk to the amount of bone growth. Ewing's sarcoma is rare in black populations (USA and Africa) and in eastern Asia. Compared with osteosarcoma, a lower percentage of tumours is localized to the long bones, and incidence rises less steeply with age and is accompanied by an increasing proportion of pelvic tumours. Chondrosarcoma is a rare cancer in children (less than 5% of bone cancers), with an age distribution similar to that of osteosarcoma and a sub-site distribution resembling that of Ewing's sarcoma. Little is known of the aetiology of these tumours; there is clearly a strong genetic predisposition in Ewing's sarcoma but, although the proportion of osteosarcoma cases of genetic origin seems to be small, environmental determinants so far suspected can account for only a small fraction of the total cases.