IHC-breast cancer subtypes of invasive ductal carcinoma with predominant intraductal component as an insignificant prognostic factor: A register-based study from Korea

Background: Invasive ductal carcinoma with predominant intraductal component (DCIS-IDC) has a favorable survival outcome. However, whether subtypes of DCIS-IDC have prognostic significance remains unknown. We assessed the prognostic value of immunohistochemical subtypes in DCIS-IDC compared with DCIS or IDC without predominant intraductal component. Methods: We retrospectively studied 37,049 early breast cancer patients enrolled in the Korean Breast Cancer Registry between January 1993 and February 2011. We categorized DCIS, DCIS-IDC and IDC by estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2) expressions, such as luminal A, B, HER2 and Triple negative breast cancer(TNBC). Multivariate Cox regression analysis was used to estimate associations between subtypes and survival. Results: In total, 8346 patients (26.3%) had DCIS, 20,427 (64.4%) had IDC and 2938 (9.3%) had DCIS-IDC. Luminal A type was the most predominant type in all three groups (DCIS=66.5%, IDC=64.7%, DCIS-IDC=46.9%). HER2 subtype was more frequent in DCIS-IDC (27.0%) than in IDC (8.3%) and DCIS (13.3%) (p<0.001). TNBC subtype was more frequent in IDC (18.0%) than in DCIS (8.5%) and DCIS-IDC (12.7%) (p<0.001). Breast cancer subtypes showed significant differences in breast cancer specific survival in IDC. HER2/neu typed DCIS showed a poor prognostic effect in overall survival, but no differences were observed in DCIS-IDC before or after adjusted by adjuvant treatments. Conclusions: Different distribution of subtypes and indistinct prognostic effects in DCIS-IDC indicates that DCIS-IDC is a distinct clinical and biological entity from pure IDC or pure DCIS. MicroAbstract: Through a large-sized, registery-based study, we reported differences of IHC-breast cancer subtypes or outcomes in pure IDC, pure DCIS and mixed DCIS-IDC cases with a predominant DCIS component (more than 80% of tumor was DCIS). IHC-breast cancer subtypes of invasive ductal carcinoma with predominant intraductal component were not significant prognostic factor unlike either pure IDC or DCIS. Clinical Practice points: We subdivide breast cancer into pure IDC (64%), pure DCIS (26%) and mixed DCIS-IDC cases (9%) with a predominant DCIS component (more than 80% of tumor was DCIS). Within IDC, they observed differences in outcome that correlated with phenotype, among approximately 37,000 cases entered into the Korean cancer registry. They did not observe statistical differences in outcome with phenotypes for the DCIS-IDC group. This study supports that there is a biologic difference between DCIS-IDC cases compared to pure DCIS or pure IDC.