HOW MUCH NEGATIVE MARGIN IS ENOUGH FOR PATIENTS WITH DUCTAL CARCINOMA IN SITU RECEIVING BREAST CONSERVING SURGERY WITH OR WITHOUT RADIOTHERAPY? A BAYESIAN META-ANALYSIS

Purpose: There is no consensus in the surgical literature about whether there is a minimum width of negative margin that is associated with optimum reduction in risk of ipsilateral breast tumor recurrence (IBTR) for women  with ductal carcinoma in situ (DCIS) treated with breast conserving surgery (BCS).

Method: We conducted a comprehensive search of published studies that examined the relationship between IBTR and margin status after BCS for DCIS. We stratified the abstracted data from 21 studies of women treated with BCS with or without radiotherapy. We applied a Bayesian approach to investigate the effect of width of negative margin on IBTR. To deal with the considerable variability across studies in how margin status was defined, we categorized margin less than 1-mm or 0-mm as positive, and correspondingly larger than 1-mm or 0-mm as negative. We also constructed six mutually exclusive categories of positive margin, negative margin, margin 0-2 mm, margin >2-mm, margin 2-10mm and margin>10-mm to examine specific margin thresholds.

Result: Of the 7582 patients identified, 3110 received BCS alone and 4472 BCS with radiotherapy. Patients with negative margins were less likely to experience IBTR than patients with positive margin: Odds ratio (OR) = 0.48; 95% credible interval (CI) 0.35-0.63 in patients with radiotherapy; and OR = 0.55; 95% CI 0.37-0.76 in patients without radiotherapy. Specific margin thresholds were further examined using a Bayesian hierarchical model for indirect comparisons. The IBTR in patients with greater than 2-mm margin was better than that in patients with a negative margin. Using patients with positive margin as the reference group, we found a probability of 0.97 that the OR for negative margin is larger than the OR for margins greater than 2-mm in patients receiving BCS with radiotherapy and 0.83 in patients without radiotherapy. The probability that the OR for margins greater than 2-mm is larger than OR for margins greater than 10-mm is 0.34 in patients receiving BCS with radiotherapy and 0.38 in patients without radiotherapy.

Conclusion: A 2-mm surgical margin free of DCIS should be obtained after BCS in order to achieve maximum reduction of risk of IBTR. More studies are warranted to understand whether wider margins are necessary.