DNA repair and its possible involvement in the origin of multiple cancer.

Multiple skin cancers and other cancers in patients with xeroderma pigmentosum (XP) were investigated in relation to DNA repair defects in the cells of the patients. Multiple skin cancers of the same or different histopathological types were found in many patients and six patients had cancers, one each, in organs other than the skin. The frequency of basal cell carcinoma was higher than that of squamous cell carcinoma in XP patients, while the two types were reported to be approximately equal in frequency in all skin cancers in Japanese. Defect in the excision-resynthesis type of repair presumably enhances the error-prone type of repair of DNA damage in XP patients and may lead to the development of cancer. Although a similar DNA repair defect of damage caused by ionizing radiation has been suspected in ataxia telangiectasia (AT), induction of mutation by gamma-rays in AT cells was lower than that in normal cells at the same survival levels. The high incidence of malignancy in AT patients could be due to factors not associated with DNA repair.