Long-term conditional relative survival trends in extrahepatic bile duct cancer: insights from a population-based retrospective cohort study in a high-incidence Asian Country, 1999–2021

Background: Dynamic prognostic information is crucial for treatment decisions and patient consultations in extrahepatic bile duct (EHBD) cancer, given its poor prognosis. This study aimed to investigate the long-term conditional relative survival (CRS) rates among patients with EHBD cancer in Korea, where its incidence is notably high. Materials and methods: Data from 46 916 individuals diagnosed with EHBD cancer between 1999 and 2021 were obtained from the Korea Central Cancer Registry (KCCR) for this retrospective cohort study. CRS was analyzed according to various strata, including the Surveillance, Epidemiology, and End Results (SEER) stage and the first course of treatment. Results: The 5-year survival probability at diagnosis was 20.8%, whereas the conditional probability of surviving to the fifth year for patients who had already survived 1, 2, 3, and 4 years after diagnosis (the probability of surviving an additional 4, 3, 2, and 1 year) was 35.4%, 55.5%, 74.0%, and 88.6%, respectively. Among the 5-year survivors, 72.4% lived for an additional 5 years. For patients who underwent surgery at the localized or regional stage, the 5-year survival rates at diagnosis were 53.5% and 34.7%, respectively. Among 2-year survivors, 71.7% (localized) and 56.6% (regional) survived to the 5 years after diagnosis, and among 5-year survivors, 73.0% (localized) and 69.0% (regional) lived for an additional 5 years. Conclusion: The long-term survival rate among patients with EHBD cancer did not plateau, even among 5-year survivors with localized-stage disease, as it continued to decline over time. These findings suggest that continued surveillance and individualized assessments are warranted for patients with EHBD cancer throughout long-term follow-up.