Different Patterns of Conditional Survival of Breast Cancer Patients by Age and Histologic types: Evidence from the Korean Nationwide Registry.

Background: Conditional relative survival (CRS), which is the survival estimate of patients who have already survived for a certain period of time after diagnosis, could provide more relevant information on the current prognosis of cancer survivors than the standard 5-year relative survival (RS). This study aimed to estimate the 5-year CRS of Korean breast cancer patients. Methods: We identified 145,083 breast cancer cases diagnosed between 2002 and 2013 in the Korea Central Cancer Registry. The CRS was estimated for every year after diagnosis, according to sex, age, histologic type, and stage. Results: The 5-year RS at diagnosis was 90.8%, and the 10-year RS was 85.7%. The 5-year CRS was 91.0% and 94.3% at 1 year and 5 years after diagnosis, respectively. Very young and very old patients had worse 5-year CRS after 5 years of survival than those of other age groups (92.2% in the <40-year and 92.6% in the >= 70-year groups vs. 95.4% in 40-49-year, 94.3% in 50-59-year, and 93.7% in 60-69-year groups). The 5-year CRS of metaplastic carcinoma increased from 82.0% at diagnosis to 95.2% at 5 years after diagnosis, compared with that of lobular carcinoma (from 93.1% to 92.5%). Hardly any excess mortality (5-year CRS >= 95%) was seen within 7 years after diagnosis. Conclusions: This study shows that the CRS of breast cancer survivors in Korea has increased, but varies by sex, age, stage, and histologic type. Impact: These findings provide more detailed information to breast cancer survivors and clinicians.