Survival Improvement in Korean Breast Cancer Patients Due to Increases in Early-Stage Cancers and Hormone Receptor Positive/HER2 Negative Subtypes: A Nationwide Registry-Based Study

PURPOSE: The aim of this study was to investigate whether the observed changes over time in the survival rates vary according to the intrinsic subtypes of breast cancer diagnosed. METHODS: Data from 46,320 breast cancer patients in the Korean Breast Cancer Registry who underwent surgery between 1999 and 2006 were reviewed. Among them, results from 25,887 patients with available data about the status of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2) were analyzed. Patients were classified into two cohorts according to the year in which they underwent surgery: 1999-2002 and 2003-2006. RESULTS: The patients treated in the latter time period showed significantly better overall survival (OS) compared with those in the former period when adjusted for follow-up duration. The proportion of hormone receptor+/HER2-subtype and stage I breast cancer were significantly higher in the latter period (47.4% vs. 54.6%, p<0.001; 31.0% vs. 39.6%, p<0.001, respectively). Improvement in OS between the former and latter periods was seen in all subtypes of breast cancer, including triple-negative cancers (all p-values <0.001 in univariate and multivariate analyses). CONCLUSION: Improvement in survival in Korean breast cancer patients over the study years is being observed in all subtypes of breast cancer, implying that increases in both early-stage detection and the proportion of less aggressive cancers contribute to this improvement.