In order to assess the influence of loss of allelic bax on c-Myc-induced apoptosis and tumorigenesis in the mammary gland, 10—week-old female study mice (myc bax+/+, n=10; myc bax+/−, n=9; myc bax−/−, n=10) were housed with male mice, bred repetitively, and followed bi-weekly for evidence of mammary tumour development. This evidence concerns the gene BAX and breast cancer.