an GENOME INTEGRITY

The incidence of breast cancer increases dramatically with age. We have generated a large collection of cul-tured normal human mammary epithelial cells (HMEC) strains to better understand whether the aging process alters, the mammary epithelia in potentially deleterious ways [1]. This resource consists of multiple strains of normal finite lifespan pre-stasis HMEC established from discarded reduction mammoplasty and peripheral to tumour mastectomy tissues from women aged 16 to 91 years. Evaluation of lineage distributions within this diverse collection of pre-stasis HMEC strains revealed that, whereas myoepithelial (MEP) cells decreased proportionately, luminal epithelial (LEP) and cKit-expressing progenitors (cKit+) with a differentiation defect increased proportionately with age; comparison to uncultured samples and tissue specimens confirmed those changes also occur in vivo. Myoepithelial cells are thought to be tumour-suppressive [2,3], and * Correspondence