Prognostic value of ductal carcinoma in situ component in invasive ductal carcinoma of the breast: a Surveillance, Epidemiology, and End Results database analysis

Background: The prognostic implication of concomitant ductal carcinoma in situ (DCIS) in invasive ductal carcinoma (IDC) remains controversial. Our objective was to investigate whether concomitant DCIS affects survival outcomes in patients with IDC. Materials and methods: Patients with nonmetastatic breast cancer who underwent surgery in 2010-2014 were included from the Surveillance, Epidemiology, and End Results program. Statistical analyses were conducted using chi(2) test, linear-by-linear association, one-way analysis of variance, Kaplan-Meier method, Cox proportional hazards regression model, and propensity score matching (PSM). Results: A total of 61,745 patients were identified, including 44,630 (72.3%), 13,559 (22.0%), and 3,556 (5.7%) patients with no DCIS component reported (No-DCIS), DCIS <25% (L-DCIS), and >= 25% (H-DCIS), respectively. Patients with H-DCIS were more likely to be younger (p<0.001), have smaller tumors (p<0.001), good/moderate differentiation (p<0.001), human epidermal growth factor receptor 2-positive disease (p<0.001), receive mastectomy (p<0.001), and not receive radiotherapy (p<0.001) and chemotherapy (p<0.001). The median follow-up was 27 months, and the 2-year breast cancer-specific survival (BCSS) in patients with No-DCIS, L-DCIS, and H-DCIS was 97.3%, 98.0%, and 98.5%, respectively (p<0.001). Before PSM, H-DCIS was an independent favorable prognostic factor for BCSS; patients with H-DCIS had better BCSS compared to patients with No-DCIS (hazard ratio [HR] 0.674, 95% CI: 0.528-0.861, p=0.002), while the BCSS between No-DCIS and L-DCIS was similar (HR 0.944, 95% CI: 0.840-1.061, p=0.334). However, this survival advantage disappeared after PSM; there was significantly different BCSS between patients with No-DCIS and H-DCIS (HR 0.923, 95% CI: 0.653-1.304, p=0.650). H-DCIS was not associated with BCSS as compared to No-DCIS in the breast-conserving surgery (p=0.295) and mastectomy (p=0.793) groups. Conclusion: In breast cancer, patients with H-DCIS have unique clinicopathologic features compared to patients with No-DCIS. Before PSM, H-DCIS was associated with favorable BCSS as compared to No-DCIS. However, the survival advantage disappeared after PSM.