Transformation and maturation of breast tissue has been a signal part of mammalian evolution.

Histological maturity of the breast occurs with lactation. Formula feeding and shorter durations of breastfeeding have  been associated with a poorer prognosis and a higher death rate from breast cancer.

The maturation of progenitor cells in the breast requires preferably at least 6 months of lactation for their optimal development with a clear improvement shown in cancer statistics.

Normal maturation of these cells appears to be associated with a lower risk of developing aggressive hormone receptor negative  types of breast cancer, and more commonly luminal A tumours responding well to hormone therapy.

A 30% decrease in risk of breast cancer recurrence with breastfeeding more than 6 months and a 28% death rate reduction has been reported.

J Nat Cancer Inst  Kwan M L et al 2015:107 Annals of Oncology 2015

Reset of cellular morphology with lactation and weaning sometime after 6 months

The Lancet 2002;360 (9328), 187-195 Formula feeding and breast cancer.