Multiple Primary Cancer and Survival after Lumpectomy with or without Radiotherapy for Ductal Carcinoma in Situ: A Propensity Score Matching Case-Control Study

Abstract Background: Radiotherapy combined with breast-conserving surgery is widely performed in patients with ductal carcinoma in situ (DCIS). This research was conducted to evaluate the use of radiotherapy to reduce the risk of MPC and mortality in DCIS patients.Methods: 128,416 patients first diagnosed with DCIS between 1998 and 2015 who received lumpectomy in the Surveillance, Epidemiology, and End Results (SEER) 18 database were included. Information on age, race, year of diagnosis, laterality, pathologic grade, surgery, radiation, estrogen receptor status, progesterone receptor status, tumor size and vital status was extracted. A comparison of lumpectomy alone vs. lumpectomy plus radiotherapy was performed using 1:1 propensity score-based matching.Results: Of the 128,416 patients with DCIS, 39,039 patients were treated with lumpectomy alone, and 69,377 were treated with lumpectomy and radiotherapy. The adjusted hazard ratio (HR) for death was 0.801 (95%CI: 0.7728-0.8301) and 0.7444 (95%CI: 0.7139-0.7761) for occurrence of MPC in the lumpectomy and radiotherapy vs. lumpectomy alone groups, respectively. Radiotherapy decreased the standardized incidence ratio (SIR) of MPC from 1.36 to 1.34. The incidence rate of a second breast cancer was reduced by 1.83% with radiotherapy (from 5.93% (2,177/36,688) to 4.10% (1,504/36,688)) in the matched cohort. Conclusion: Lumpectomy plus radiotherapy is associated with a significant reduction in mortality and risk of MPC, mainly second primary BC. Of those patients younger than 40 years, Black women with high-grade tumors were likely to benefit most. Radiotherapy reduced the risk of occurrence rather than the mortality of MPC patients to reduce the overall mortality.