Implications of New Lumpectomy Margin Guidelines for Breast-Conserving Surgery: Changes in Reexcision Rates and Predicted Rates of Residual Tumor.

Background: The 2014 guidelines endorsed by Society of Surgical Oncology, the American Society of Breast Surgeons, and the American Society for Radiation Oncology advocate "no ink on tumor" as the new margin requirement for breast-conserving therapy (BCT). We used our lumpectomy margins database from 2004 to 2006 to predict the effect of these new guidelines on BCT.
Methods: Patients with neoadjuvant therapy, pure ductal carcinoma-in situ, or incomplete margin data were excluded. We applied new ("no ink on tumor") and old (≥2 mm) margin guidelines and compared rates of positive margins, reexcision, and rates of residual disease found at reexcision.
Results: A total of 437 lumpectomy surgeries met the eligibility criteria. Eighty-six percent had invasive ductal carcinoma, 12% invasive lobular carcinoma, and 2% invasive ductal carcinoma and invasive lobular carcinoma. Using a ≥2 mm margin standard, 36% of lumpectomies had positive margins compared to 18% using new guidelines (p < 0.0001). Seventy-seven percent of patients with "ink on tumor" had residual disease found at reexcision. Fifty percent of subjects with margins <2 mm had residual disease (p = 0.0013) but would not have undergone reexcision under the new guidelines. With margins of ≥2 mm, residual tumor was seen in the shaved margins of 14% of lumpectomies. Residual tumor was more common in reexcisions for ductal carcinoma-in situ <2 mm from a margin than for invasive cancer (53 vs. 40%), although this was not statistically significant.
Conclusions: Use of new lumpectomy margin guidelines would have reduced reoperation for BCT by half in our patient cohort. However, residual disease was present in many patients who would not have been reexcised with the new guidelines. Long-term follow-up of local recurrence rates is needed to determine if this increase in residual disease is clinically significant.