Long breastfeeding has been shown to be associated with decreased risk of breast cancer in humans, but the mechansim of this effect was also unknown.

Dr. Germain’s group studied mice, looking at Pappalysin-1, a protien encoded by the PAPPA gene in humans. They discovered that mice that express Pappalysin-1 in their mammary gland develop mammary tumors, but only following pregnancy. They also discovered that long but not short lactation inhibits this effect of Pappalysin-1. The Germain group reported that molecules produced during lactation can block the action of Pappalysin-1.

This is the very first mechanism that explains the protective effect of breastfeeding. Dr. Germain and her lab are working to isolate what they have now identified as a hormone that protects against breast cancer. Isolation and potential application of this hormone in a patient setting is the goal.

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