In mammary adenocarcinomas, the levels of apoptosis were significantly different for each of the three evaluated genotypes (P=0.001 for myc bax+/+ vs myc bax+/−; P=0.033 for myc bax+/− vs myc bax−/−; and P=0.017 for myc bax+/+ vs myc bax−/−) as well as between the adenocarcinomas and dysplastic mammary lesions in tumour-bearing, parous MMTV-c-myc/bax-hemizygous study mice (P=0.001). The gene discussed is BAX; the disease is breast adenocarcinoma.