Prognostic Score-Based Stratification Analysis Reveals Universal Benefits of Radiotherapy on Lowering the Risk of Ipsilateral Breast Event for Ductal Carcinoma In Situ Patients with Different Risk Levels.

Abstract

We aimed to analyze the effects of radiotherapy (RT) on the incidence rate of ipsilateral breast event (IBE) in ductal carcinoma in situ (DCIS) patients with lumpectomy after being stratified by prognostic score. We identified DCIS patients who received lumpectomy, from the Surveillance, Epidemiology, and End Results (SEER) database from 1988 to 2015. Cumulative incidence functions for competing risk were used to evaluate the effects of RT on IBE risk over time. Three multivariate regression models (weighted, non-weighted, and Fine-Gray) were applied to compare the IBE risk between the RT and non-RT groups after stratifying patients by prognostic score. Overall, 72,623 DCIS patients were identified from the SEER database and 49,206 (66.8%) patients received RT. During the follow-up period (ranging from 7 to 347months), the cumulative probability of invasive and in situ IBE was significantly lower in the RT group than in the non-RT group (p < 0.001). After being stratified by prognostic score, the weighted IBE incidence rate increased as the risk level increased (p < 0.050). In multivariate regression models, RT lowered the IBE incidence rate by at least 30% in low-, moderate-, and high-risk DCIS (p < 0.010). In particular, the in situ and invasive IBE incidence rate decreased by over 50% in low-risk DCIS with RT (p < 0.001). RT is associated with a lowered IBE incidence rate in DCIS patients, regardless of the assigned risk levels for patients. The significant reduction in the IBE incidence rate in low-risk DCIS patients also indicates the potential benefits for recommending RT to such a patient population in clinical practice.