Although many oncogenic drivers for tumourigenesis remain elusive, because the absence of Brca1 initially triggers the lethal block by inducing mitotic catastrophe and apoptosis, researchers have hypothesised the existence of secondary “hits” to modifying some cancer drivers (oncogenes or tumour suppressors) to attenuate this block, allowing Brca1-mutant cells to overcome mitotic catastrophe and ultimately resulting in mammary tumourigenesis18. This evidence concerns the gene BRCA1 and cancer.