Cancer in homozygotes and heterozygotes of ataxia-telangiectasia and xeroderma pigmentosum in Britain.

We have documented mortality and cancer incidence in the families of 67 patients with ataxia-telangiectasia and 48 patients with xeroderma pigmentosum resident in Britain. For both diseases, parents of patients are obligate heterozygotes and grandparents have a probability of heterozygosity of 0.5. Fourteen ataxia-telangiectasia patients had died by June 30, 1986. This was a significant excess (14 deaths observed, 1.65 expected). Only one death was from a malignancy (non-Hodgkin's lymphoma). Three parents of ataxia-telangiectasia patients had died, all from cancer. The excess from breast cancer (two deaths observed, 0.17 expected) was statistically significant, p less than 0.05. However, no excess mortality from malignant neoplasms was found in the grandparents. Five xeroderma pigmentosum patients had died, none from internal malignancies. No excess mortality from malignant neoplasms was recorded in either their parents or grandparents.