Some breast cancers are thought to arise from mammary stem cells that mutate, but a study published in this week's Nature Medicine indicates that luminal cells that line the mammary ducts may also be tumor progenitors.

Basal-like breast cancers arise in women carrying mutations in the gene encoding the tumor suppressor protein BRCA1. Jane Visvader and her colleagues isolated distinct cell populations from normal mammary tissue and pre-cancerous tissue from women who have one normal BRCA1 gene and one BRCA1 gene mutation. They found that breast tissue from BRCA1 mutation women harbors an expanded luminal progenitor population. Analysis of gene expression patterns showed that basal breast cancer tumor cells were more similar to the luminal progenitor cells than to any other cell type, including the stem cell population.

The discovery of an aberrant luminal progenitor population in pre-cancerous tissue from BRCA1 mutation carriers establishes these cells as a probable target population in the fight against such breast tumors.