Do All Positive Margins in Breast Cancer Patients Undergoing a Partial Mastectomy Need to Be Resected?

Positive margins have been reported in 20% to 40% of patients undergoing a partial mastectomy, often resulting in re-excision. How often the re-excision yields additional cancer and whether there are predictors of residual disease remain unknown.

Patients who had a positive margin (defined as tumor at ink for patients with invasive disease or within 1 mm for patients with ductal carcinoma in situ) in the SHAVE (A Randomized Controlled Trial of Routine Shave Margins Versus Standard Partial Mastectomy in Breast Cancer Patients) trial before randomization were evaluated to determine the rate of additional disease either in cavity shave margins or at re-excision. Details of the SHAVE trial can be found elsewhere.

Of the 235 patients in the trial, 82 (34.9%) had a positive margin before randomization; 58 of these patients underwent either cavity shave margins excision or a re-excision of the positive margin(s). Twenty-one (36.2%) patients had residual disease. On bivariate analysis, residual disease was associated with younger patient age (median 51 vs 62 years; p = 0.007), and the presence of high-grade ductal carcinoma in situ (57.1% vs 31.3% for grade 2 and 0% for grade 1; p = 0.025). The following factors were not associated with further disease: patient race; ethnicity; BMI; volume of resection; number of positive margins; extent of ductal carcinoma in situ; and extent, grade, and histologic subtype of invasive cancer. On multivariate analysis, only patient age younger than 60 years remained a significant predictor of residual disease (odds ratio 3.920; 95% CI 1.081 to 14.220; p = 0.038).

Positive margins are associated with further disease in more than one-third of patients and, aside from young age, there are no predictors of this. These findings support continued re-excision of positive margins, particularly in patients younger than 60 years of age.