Previous studies have reported the incidence of mammary tumours in single strain, multiparous MMTV-c-myc mice as approaching 100%; however, no studies of MMTV-c-myc transgenic or myc-containing bitransgenic mice have reported mammary tumour multiplicity findings (Stewart et al, 1984; Jamerson et al, 2000). Here, MYC is linked to breast cancer.