Prophylactic nipple-sparing mastectomy leaves more terminal duct lobular units in situ as compared with skin-sparing mastectomy.

Prophylactic skin-sparing mastectomy (SSM) is associated with major breast cancer risk reduction in high-risk patients. In prophylactic nipple-sparing mastectomy (NSM) it is unknown how many terminal duct lobular units (TDLUs) remain behind the nipple-areola complex (NAC) additionally to those behind the skin flap. Therefore, safety of NSM can be doubted. We compared amounts of TDLUs behind the NAC as compared with the skin. In prophylactic SSM and conventional therapeutic mastectomy patients, the NAC and an adjacent skin island (SI) were resected as if it were an NSM. NAC and SI were serially sectioned perpendicularly to the skin and analyzed for the amount of TDLUs present. Slides of NAC and SI were scanned, and slide surface areas (cm) were measured. TDLUs/cm in NAC versus SI specimen, representing TDLU density, were analyzed pairwise. In total, 105 NACs and SIs of 90 women were analyzed. Sixty-four NACs (61%) versus 25 SIs (24%) contained ≥1 TDLUs. Median TDLU density was higher in NAC specimens (0.2 TDLUs/cm) as compared with SI specimens (0.0 TDLUs/cm; P<0.01). Independent risk factors for the presence of TDLUs in the NAC specimen were younger age and parity (vs. nulliparity). The finding of higher TDLU density behind the NAC as compared with the skin flap suggests that sparing the NAC in prophylactic NSM in high-risk patients possibly may increase postoperative breast cancer risk as compared with prophylactic SSM. Studies with long-term follow-up after NSM are warranted to estimate the level of residual risk.