Effect of mammography screening on long-term survival of breast cancer patients: Results from the National Cancer Screening Program in Korea

Background: Breast cancer (BC) is the most commonly diagnosed cancer type globally with the geo-ethnic differences in BC epidemiology. Therefore, many countries have adopted national cancer screening programs to reduce the burden of BC. Currently, the Korean National Cancer Screening Program provides biannual mammography screening for women aged ≥40 years. However, there were limited Asian studies investigating the effect of mammography screening, especially study with the long-term follow-up. Our study investigated the effect of mammography on the long-term survival of BC patients aged 40 years or older according to the screening history and duration since screening. Methods: The study cohort was organized from three nationwide databases of the Korean National Cancer Screening Program, the Korean Central Cancer Registry, and death certificates. We included 24,387 women diagnosed with invasive cancer or ductal carcinoma in situ in 2008 and 2009 and followed up until December 31, 2019. The Kaplan–Meier analysis and the log-rank test were used to compare the survival of the subgroups. Cox proportional-hazards regression was used to investigate the effect of BC screening on mortality. Results: Overall, 20,916/24,387 patients (85.8%) were alive at the end of the follow-up period (median: 10.5 years). The long-term survival rate was significantly lower in the never-screened group (80.3%) than in the screened group (88.9%) (P<0.001). The survival rate ranged from only 22.4% in patients with distant stage to 96.4% in DCIS patients. A 35% BC mortality reduction (hazard ratio [HR]=0.65, 95% confidence interval [CI]=0.60–0.70) from screening was observed. Subgroup analysis based on cancer stage showed reductions of 62%, 36%, and 24% for subgroups of localized stage, regional stage, and distant stage, respectively. Women aged 40–49 years received the least benefit from BC screening (HR=0.71, 95% CI=0.62–0.81). Conclusions: Mammography screening was effective in reducing the risk of BC-specific death in Asian women across all cancer stages. However, this effect was relatively small among women in their 40s, suggesting that more detailed and specialized screening strategies are needed.