Early Adoption of the SSO-ASTRO Consensus Guidelines on Margins for Breast-Conserving Surgery with Whole-Breast Irradiation in Stage I and II Invasive Breast Cancer: Initial Experience from Memorial Sloan Kettering Cancer Center.

Background: Reexcision rates in patients undergoing breast-conserving surgery (BCS) for early-stage invasive breast cancer are highly variable. The Society of Surgical Oncology (SSO) and American Society for Radiation Oncology (ASTRO) published consensus guidelines to help standardize practice. We sought to determine reexcision rates before and after guideline adoption at our institution.

Methods: We identified patients with stage I or II invasive breast cancer initially treated with BCS between June 1, 2013, and October 31, 2014. Margins were defined as positive (tumor on ink), close (≤1 mm), or negative (>1 mm), and were recorded for both invasive cancer and ductal carcinoma-in situ (DCIS) components. Reexcision rates were quantified, characteristics were compared between groups, and multivariable logistic regression was performed.

Results: A total of 1205 patients were identified, 504 before and 701 after the guideline adoption (January 1, 2014). Clinical and pathologic characteristics were similar between time periods. Reexcision rates significantly declined from 21.4 to 15.1 % (p = 0.006) after guideline adoption. A multivariable model identified extensive intraductal component (odds ratio [OR] 2.5, 95 % confidence interval [CI] 1.2-5.2), multifocality (OR 2.0, 95 % CI 1.2-3.6), positive (OR 844.4, 95 % CI 226.3-5562.5) and close (OR 38.3, 95 % CI 21.5-71.8) ductal carcinoma-in situ margin, positive (OR 174.2, 95 % CI 66.2-530.0) and close (OR 6.4, 95 % CI 3.0-13.6) invasive margin, and time period (OR 0.5, 95 % CI 0.3-0.9 for post vs. pre) as independently associated with reexcision.

Conclusions: Overall reexcision rates declined significantly after guideline adoption. Close invasive margins were associated with higher rates of reexcision than negative invasive margins in both time periods; however, the effect diminished in the postguideline adoption period. Thus, we expect continued decline in reexcision rates as adherence to guidelines becomes more uniform.