The association between surgical margins and local recurrence in women with ductal carcinoma in situ treated with breast conserving therapy: Observational study

Introduction: The incidence of DCIS (DCIS) constitutes 25 % of the newly identified breast cancers. Approximately 35 % of DCIS cases are detected in asymptomatic women during routine mammography screening. The 20-year breast-cancer-specific mortality rate was 3.3 %. Breast-conserving surgery(BCS), followed by radiotherapy, is the treatment of choice. However, an adequate margin for BCS remains unclear. Therefore, we need to investigate the relationship between the margin distance and cancer recurrence. Methods: A total of 4,355 patients with DCIS were assessed between January 1, 2010, and January 31, 2020. Of these, 4,123 patients who had invasive ductal carcinoma co-existing DCIS and who were treated with mastectomy were excluded. Thus, 232 patients with pure DCIS treated with BCS were included. All distant radial margins were measured. Results: A total of 232 patients with DCIS underwent breast-conserving surgery, 169 patients received whole breast radiotherapy, and 63 did not. Most patients received hormone therapy, and as indicated, the median follow-up was 73 months. Recurrence was observed in seven patients. Among them, four had margins <2 mm, while the others had margins > 2 mm. There were no significant differences in disease-free survival (DFS) among the margin statuses. Conclusion: Margins wider than 2 mm did not demonstrate a reduction in local recurrence for women receiving adjuvant whole-breast radiation therapy, supporting the recommendation of a negative margin threshold for surgical management of DCIS.