Rising Incidence of Intrahepatic Bile Duct Cancer Among Adults Aged 50 Years and Older: A SEER 1975–2022 Analysis

Intrahepatic bile duct cancer (iCCA) is a rare but aggressive malignancy with increasing global awareness. Age remains a major risk factor, yet long-term U.S. trends among older adults have not been well characterized. This study evaluates 48 years of incidence trends specifically among individuals aged ≥50 years.

We extracted annual case counts and population estimates for intrahepatic bile duct cancer from the SEER 8 Registries (1975–2022). Only cases in adults aged ≥50 were included. Crude incidence rates per 1,000,000 population were calculated annually. Temporal trends were analyzed using simple linear regression, with year as a continuous independent variable.

Across the study period, incidence among the ≥50 population ranged from approximately 2 to 8 cases per 1,000,000, with notable year-to-year variability. A mild upward trajectory was observed visually, and regression analysis demonstrated a positive slope (β ≈ ___; exact values pending model output). Whether this increase was statistically significant will depend on the regression p-value from the user's output.

Notably, the incidence remained consistently higher than that seen in younger age groups in parallel analyses.

In adults aged 50 years and older, the incidence of intrahepatic bile duct cancer has shown a mild long-term upward trend over the past five decades. Although annual fluctuations are substantial, the overall pattern suggests a gradual increase, highlighting the importance of continued surveillance and evaluation of age-related risk factors.