While there is a paucity of information regarding lactation in the setting of benign breast disease, lactation generally is possible and successful.  Non-proliferative benign breast disease that affects people of childbearing age includes but is not limited to fibroepithelial lesions, hamartomas, cysts, and idiopathic granulomatous mastitis (IGM).  Proliferative breast disease, both with atypia and without atypia, may also present in lactating people.  An example of proliferative breast disease without atypia is a radial scar or complex sclerosing lesion, while an example of a proliferative disease with atypia is atypical ductal hyperplasia (ADH).¹

While these lesions themselves do not preclude lactation, those with atypia may sometimes need to use endocrine therapy (e.g. tamoxifen, a Selective Estrogen Receptor Modulator, or SERM) to reduce future risk of breast cancer development.  SERM’s are known to inhibit lactogenesis II.  There is no data regarding transfer into breastmilk and therefore they are not recommended during lactation.² Patients should engage in shared decision making regarding the benefit of SERMs versus the risk-reducing benefits of breastfeeding, which is most significant in those with a first-degree relative with breast cancer³ and those with a BRCA I mutation.⁴

It should be noted that if a mass is in close proximity to the nipple areolar complex prior to pregnancy, it may present a challenge for lactation if it interferes with latch or obstructs the retroareolar region.  Therefore, we recommend these patients be referred for evaluation by a breast surgeon and breastfeeding and lactation medicine specialist to determine whether the risk of removal and potential damage to underlying parenchyma, lymphatics, and neurovascular structures outweighs the risk of the mass itself causing a significant breastfeeding complication.⁵ If the patient does undergo surgical excision, they should be referred to lactation during pregnancy and be monitored closely in the postpartum period for assistance with lactation.

For more detailed information and references on specific medications including specific SERMs, please refer to LactMed, e-lactancia, Infant Risk, or Mother to Baby.