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Background: The results of the ACOSOG- Z0011 trial have had potential practice changing implications for the management of patients with positive sentinel lymph node (SLN) undergoing lumpectomy and radiation for breast cancer. However, some evidence suggests a shift in axillary management even prior to the initial report of data supporting sentinel lymph node biopsy (SLNB) alone in mid-2010. We analyzed data in the National Comprehensive Cancer Network (NCCN) outcomes database from NCCN centers and the Michigan Breast Oncology Quality Initiative (MiBOQI) hospitals to examine institutional practice patterns with respect to use of completion axillary dissection (CALND) for SLN positive breast cancer in the years leading up to publication of these trial results. We hypothesized that CALND would be omitted more frequently in women treated at NCCN centers compared to those treated at MiBOQI programs. Methods: We identified 2,172 women with clinical T1/T2 N0 breast cancer who underwent breast surgery and SLNB and had a positive SLN from 2007 through 2010 at one of 12 participating NCCN centers or 12 MiBOQI sites. Patient and tumor characteristics, definitive breast procedure, year of diagnosis, and institutional affiliation were analyzed as predictors of use of SLNB alone in univariate Chi-Square and multivariable logistic regression models. Results: CALND was omitted in 314 (14.5%) of the 2,172 patients. Over time, there was a dramatic increase in the use of SLNB alone (12% in 2007 to 23% in 2010). In the univariate analyses, increased patient age, later year of diagnosis, lower T stage, and lower pathologic N stage were significant predictors of use of SLNB alone (all p < .0001). There was no association between definitive breast surgery type, hormone receptor status, Her-2 Neu status, or institutional affiliation and use of SLNB alone. In the multivariable model, older age at diagnosis, later year of diagnosis, and lower pathologic N stage remained significant independent predictors of SLNB alone. There were no significant differences in rates of omission of CALND between NCCN and MIBOQI sites. Conclusions: Omission of CALND occurred frequently in women with SLN positive breast cancer cared for in both NCCN and MiBOQI institutions in advance of reporting results of ACOSOG-Z0011. This shift was seen in management of patients undergoing lumpectomy as well as mastectomy. Further study is warranted to determine the extent of durable practice changes as well as any impact on survival and local-regional control. [ABSTRACT FROM AUTHOR]