Invasive ductal carcinoma with coexisting ductal carcinoma in situ (IDC/DCIS) versus pure invasive ductal carcinoma (IDC): a comparison of clinicopathological characteristics, molecular subtypes, and clinical outcomes.

PURPOSE: Ductal carcinoma in situ (DCIS) is widely recognized as the precursor of invasive ductal carcinoma (IDC). We aimed to analyze the clinicopathological characteristics and clinical outcomes of coexisting DCIS component in IDC and its clinical significance according to molecular subtypes. METHODS: Data from 3001 patients with IDC (79.4%) and IDC/DCIS (20.6%) who underwent surgery from January 2009 to June 2016 were retrospectively assessed. The clinical outcomes of IDC with coexistent DCIS in different molecular subtypes were evaluated. RESULTS: IDC/DCIS patients were more likely to be younger (P < 0.001), had low tumor grade (P = 0.001), had less lymph node involvement (P = 0.038) and received more mastectomy (P = 0.002) than IDC patients. In the comparison of molecular subtype prevalence, IDC/DCIS patients were more frequently presented with luminal B/HER2 positive (12.5% vs 11.0%, P < 0.001) and HER2 positive subtypes (20.9% vs 9.8%, P < 0.001). The 5-year disease-free survival (DFS, 90.9% vs 87.5%, P = 0.021) and 5-year overall survival (OS 96.1% vs 94.0%, P = 0.018) were significantly improved in IDC/DCIS patients compared to IDC patients. In multivariate analysis, the presence of coexisting DCIS (P = 0.048), tumor size (P < 0.001), lymph node status (P < 0.001), lymphovascular invasion (P = 0.007) and molecular subtypes (P < 0.001) were independent prognostic factors for DFS. Furthermore, coexistence of DCIS component in IDC significantly improved DFS in HER2 positive (94.8% vs 78.5%, P = 0.003), but had no association in luminal and triple negative subtypes. CONCLUSIONS: IDC with coexisting DCIS was associated with improved prognosis. Patients with IDC/DCIS presented with more HER2 positive expression and might improve DFS in HER2 positive breast cancer.