Abstract P3-12-02: Patient prognostic score and survival benefit offered by radiotherapy for ductal carcinoma in situ
Authors: Sagara Y , Freedman RA , Vaz-Luis I , Mallory MA , Wong S , Aydogan F , DeSantis S , Barry WT , Golshan M 
Published: May 2016

Background: In general, radiotherapy (RT) follows breast-conserving surgery (BCS) and remains the standard of care for the surgical management of both invasive carcinoma and ductal carcinoma in situ (DCIS). Although it is associated with better local control, the magnitude of survival benefit conferred by RT for DCIS has not yet been established. We sought to evaluate whether a survival benefit exists with the addition of RT for patients with DCIS and to validate a patient prognostic score to predict survival benefit.

Methods: We performed a retrospective longitudinal cohort study by using the Surveillance Epidemiology and End Results database (SEER 17). Between 1988-2007, we identified 32,144 eligible patients who underwent BCS for DCIS. Using age, year of diagnosis, race, tumor size, hormone receptor status, tumor grade, marital status and SEER region, we calculated propensity score weights to balance clinicopathologic factors between patients receiving only surgery and those receiving surgery and RT. This cohort was divided into seven groups according to the previously validated patient prognostic score proposed by Smith et al. Breast cancer mortality (BCM) was assessed using a log-rank test and a multivariable Cox proportional hazards model.

Results: Of 32,144 cases of DCIS, 20,329 cases (63%) were treated with RT (+RT group) and 11,815 cases (37%) were treated with surgery alone (-RT group). There were 304 breast cancer-specific deaths observed over the follow-up period (median 96 months). The weighted cumulative incidence of BCM at ten-years was 1.8% for the +RT group compared to 2.1% for the -RT group (p= 0.003). The effect of RT on survival differed by nuclear grade (p= 0.007), age (p= 0.004), and tumor size (p=0.02). We found that the survival benefit for the +RT group was significantly greater than for the –RT group in subgroups of patients with higher nuclear grade, younger age, and larger tumor size, whereas a statistical reduction of BCM with RT was not observed among patients without these prognostic factors. Moreover, the magnitude of survival benefit was significantly correlated with the patient prognostic score [p&lt;0.0001, Table].

Conclusion: In this population-based cohort study, the patient prognostic score for DCIS accurately estimated the magnitude of survival benefit offered by radiotherapy after BCS, suggesting that decisions for RT could be tailored based on prognostic score and patient preference. Limitations of this study include unmeasured confounders such as a lack of information about patients' comorbidities, margin status and endocrine therapy, and further external validation is needed to confirm our results.

Patient Prognostic Score and Hazard Ratio (HR) Comparing Mortality between Radiotherapy Group and non-Radiotherapy GroupPatient Prognostic ScoreNumber of patients in -RT groupNumber of patients in +RT groupWeighted HR of BCM95% CIWeighted HR of OM95% CI078213881.20.67 - 2.10.910.76 - 1.11267744801.00.70 - 1.50.880.78 - 0.992410570800.690.51 - 0.940.710.63 - 0.793304854170.730.48 - 1.10.680.58 - 0.81496517010.310.16 - 0.580.420.30 - 0.5852232480.290.09 - 0.910.430.21 - 0.9161515N.A. N.A. Abbreviation: RT, Radiotherapy; BCM, Breast Cancer Mortality; OM, Overall Mortality: N.A., not available

Citation Format: Sagara Y, Freedman RA, Vaz-Luis I, Mallory MA, Wong S, Aydogan F, DeSantis S, Barry WT, Golshan M. Patient prognostic score and survival benefit offered by radiotherapy for ductal carcinoma in situ. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-12-02.