Breast cancer histology and non-sentinel lymph node involvement following a positive sentinel lymph node biopsy: A multi-institutional cohort study.

1043Background: Management of the axilla in early breast cancer has shifted towards a more conservative surgical approach. The omission of a completion axillary lymph node dissection (cALND) in the context of a positive sentinel lymph node (SLN) has become common, even though this practice may result in residual non-sentinel positive nodes left behind. Furthermore, the axillary management of both invasive ductal and invasive lobular carcinomas (IDCs and ILCs) has traditionally been the same despite the different pattern of invasion and metastases in ILCs. The objective of this study was to determine if lobular histology is an independent predictor of non-sentinel lymph node (NSLN) involvement following a positive SLN biopsy (SLNB). Methods: A multi-institutional cohort study was completed. Patients with node positive IDC or ILC who were treated with both a SLNB followed by cALND from November 1997 to June 2009 were included. The primary outcome was NSLN involvement, defined as having at least one positive...