International variations in the incidence of childhood soft-tissue sarcomas.

In the study of international childhood cancer incidence coordinated by the International Agency for Research on cancer, soft-tissue sarcomas comprised between 4 and 8% of all cancers between 0 and 14 years of age. Among predominantly white populations, the age-standardised annual incidence rate (ASR) for all soft-tissue sarcomas was between 5 and 9 per million. The most common histological subtypes were rhabdomyosarcoma (ASR 4-7 per million) and fibrosarcoma, including other malignant fibromatous tumours (ASR 1-2 per million). In the United States the incidence of rhabdomyosarcoma for black girls was only half that for white girls, while the rates for boys were similar in the two ethnic groups; fibrosarcoma had a higher incidence among black people than white people for both sexes. Throughout most of Asia, soft-tissue sarcomas almost invariably had a total ASR below 6 per million, rhabdomyosarcoma and fibrosarcoma again being the most common histological types. In Africa, incidence rates could not generally be calculated, but there were substantial numbers of registrations for rhabdomyosarcoma and fibrosarcoma. The majority of cases of Kaposi's sarcoma were in African children, and in eastern and southern Africa where Kaposi's sarcoma is endemic among adult men it comprised 25-50% of soft-tissue sarcomas and 2-10% of all childhood cancers; the sex ratio (M/F) was 2.2:1, in contrast to the overwhelming male predominance among adults. Variations between ethnic groups in the incidence of rhabdomyosarcoma and fibrosarcoma, together with their occurrence in a number of heritable syndromes, suggest that genetic predisposition is important in their aetiology. There was little evidence for an environmental aetiology in rhabdomyosarcoma and fibrosarcoma but an infectious agent may be responsible for childhood Kaposi's sarcoma.