Adoption of SSO-ASTRO Margin Guidelines for Ductal Carcinoma in Situ: What Is the Impact on Use of Additional Surgery?

Background: Historically, more than one-third of patients with ductal carcinoma in situ (DCIS) treated with breast-conserving surgery (BCS) underwent additional surgery. The SSO-ASTRO guidelines advise 2 mm margins for patients with DCIS having BCS and whole-breast radiation (WBRT). Here we examine guideline impact on additional surgery and factors associated with re-excision.
Patients and Methods: Patients treated with BCS for pure DCIS from August 2015 to January 2018 were identified. Guidelines were adopted on September 1, 2016, and all patients had separately submitted cavity-shave margins. Clinicopathologic characteristics, margin status, and rates of additional surgery were examined.
Results: Among 650 patients with DCIS who attempted BCS, 50 (8%) converted to mastectomy. Of 600 who had BCS as final surgery, 336 (56%) received WBRT and comprised our study group. One hundred twenty-eight (38%) were treated pre-guideline and 208 (62%) were treated post-guideline. Characteristics and margin status were similar between groups. The re-excision rate was 38% pre-guideline adoption and 29% post-guideline adoption (p = 0.09), with 91% having only one re-excision. Re-excision for ≥ 2 mm margins was uncommon (6% pre-guideline vs. 5% post-guideline). On multivariate analysis, younger age (OR 0.97, 95% CI 0.94-0.99, p = 0.02) and larger DCIS size (OR 1.43, 95% CI 1.2-1.8, p < 0.001) were predictive of re-excision; guideline era was not. Younger age (OR 0.93, 95% CI 0.9-0.97, p < 0.001) and larger size (OR 1.64, 95% CI 1.3-2.1, p < 0.001) were predictive of conversion to mastectomy, but residual tumor burden was low.
Conclusions: The SSO-ASTRO guidelines did not significantly change re-excision rates for DCIS in our practice, likely since re-excision for margins ≥ 2 mm was uncommon even prior to guideline adoption, dissimilar to historically observed variations in surgeon practices. Younger age and larger DCIS size were associated with additional surgery.