The ovarian hormones oestrogen and progesterone increase breast cancer risk but the cellular mechanisms are unclear. Here it is shown that the size of the mammary stem cell pool in mice is regulated by steroid hormone signalling, although these cells lack the receptors for oestrogen and progesterone. The augmented pool could lead to clonal expansion of a mutated cell, possibly accounting for the increased incidence of breast cancer associated with pregnancy.
- Marie-Liesse Asselin-Labat
- François Vaillant
- Jane E. Visvader
