It is *extremely* unlikely that the breast lump in the baby is due to estrogens in the mother's milk. Why don't other 8 month old babies have it? Eh? (That's Canadian). Why didn't it show up before, presumably when the baby was breastfeeding more? Why only one side? Stop breastfeeding for three weeks! Let me tell you what the pediatrician would say if the baby were not breastfed. He would say we need a biopsy to make sure it is not a malignant tumour. It is easier to do a needle biopsy on the baby than on a woman. Jack Newman, MD, FRCPC