CCND1 and breast cancer: Extensive copy number characterisation using comparative genomic hybridisation (CGH) technology has led to remarkable insights into the somatic genetics of breast cancer, including identification of recurrent whole arm gains and losses, homozygous deletions (e.g. CDKN2A/B, PTEN) and large, common, recurrent driver amplifications (e.g. ERRB2, CCND1) [1–4].