Genetic analysis of childhood sarcoma. A survey of cancer in 159 3-year survivors of childhood soft tissue sarcoma and their relatives revealed a cancer excess in first-degree relatives primarily due to cancers occurring before the age of 35 years and a highly significant excess in relatives of patients with second malignant neoplasms. Tumors of soft tissue and bone, breast, and brain were in excess in relatives and as second malignant neoplasms in patients. To determine the most likely explanation for the observed cancer distribution, we applied segregation analysis under a unified version of the mixed model. The observed data were most compatible with a rare autosomal dominant gene with high penetrance (gene carriers had a 50% probability of cancer by age 30, increasing to 90% by age 60) as compared with a chance occurrence or a multifactorial explanation. We contrasted the relative odds of observing each pedigree under a sporadic, multifactorial, or major gene model, and identified 11 pedigrees in which familial clustering of cancer was significant, with the distribution of cancer strongly favoring a major gene in 9 pedigrees. The tumors in these kindreds have been associated with alterations in specific genetic loci by tumor-specific genetic analysis. In particular, we observed soft tissue sarcoma, osteosarcoma and premenopausal ductal breast carcinoma tumors, perhaps attributable to loss of the Rb-1 suppressor gene on chromosome 13q, in the same patients and families. Study of the cancer predisposition segregating in 10 families by genetic linkage with markers of chromosome 13q and the Rb-1 gene have to date given negative LOD scores at 0 = 0 of Z = -1.2 to -13.0.(ABSTRACT TRUNCATED AT 250 WORDS)