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 multiple primary cancer (MPC) and mortality in DCIS patients.
Methods: 108,416 patients first diagnosed with DCIS between 1998 and 2015 who received lumpectomy in the Surveillance, Epidemiology, and End Results (SEER) 18 database were included. Age, race, year of diagnosis, laterality, pathologic grade, surgery, radiation, estrogen receptor status, progesterone receptor status, tumor size and vital status were extracted. A comparison of lumpectomy vs. lumpectomy plus radiotherapy was performed using 1:1 propensity score-based matching.
Results: Of the 108,416 patients, 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 and 0.7444 for occurrence of MPC in the lumpectomy and radiotherapy vs. lumpectomy alone groups, respectively.
Conclusion: Lumpectomy plus radiotherapy is associated with a significant reduction in mortality and risk of MPC, mainly second primary BC. Younger patients, 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.