Cells from patients with ataxia telangiectasia are abnormally sensitive to the cytotoxic effect of a tumor promoter, phorbol-12-myristate-13-acetate.

Fibroblast strains from 6 patients with ataxia telangiectasia (A-T) were found to be markedly hypersensitive to the cytotoxic action of the tumor promoter phorbol-12-myristate-13-acetate (PMA), their D37 values being 5 times lower than those of two normal controls. Two A-T heterozygous strains were slightly hypersensitive to PMA, while a third one showed normal sensitivity. It is concluded that the DNA lesion which is critical in A-T cells is an important component of the damage caused by PMA-induced free radicals and may play a role both in the tumor-promoting activity of PMA and the cancer proneness of A-T patients.