Hepatitis C virus infection and the temporal trends in the risk of liver cancer: a national register-based cohort study in Sweden.

Background: In many countries, including Sweden, the birth cohorts with the highest prevalence of hepatitis C virus (HCV) infection have now reached the ages with high risk of primary liver cancer (PLC). The aims of this study were to investigate the temporal trends in PLC incidence and the relative risks of PLC among people diagnosed with HCV infection between 1990 and 2015. Methods: The HCV cohort (n = 52,853) was compared with a matched non-HCV comparison cohort (n = 523,649). Both the national Cancer Register (CR) and Cause of Death Register (DR) were used for follow-up. The crude and age-standardized PLC incidence rates were calculated. The relative risk was estimated as standardized incidence ratios (SIR) and as HRs using stratified Cox hazards regression. Results: There were 1,609 with PLC diagnosis in the HCV cohort; the annual number increased continuously with the crude incidence rate reaching 4.56 per 1,000 person-years in 2013 while remaining low and stable in the comparison cohort. In the HCV cohort, the age-standardized PLC incidence rates per 1,000 person-years remained relatively constant at 2.64 [95% confidence interval (CI), 1.54-3.75] in 2000 and 3.31 (2.51-4.12) in 2014. The highest SIR was 73 (65.979.5) among those infected for 35 to 40 years; and the highest HR was 65.9 (55.9-77.6) for men and 62.2 (31.9-121.1) for women. Conclusions: There was a considerable increase in PLC incidence over time and an extremely high relative risk in the population with HCV infection for more than 35 years. Impact: The national HCV-associated PLC incidence should be monitored in future studies to evaluate the effect of directacting antiviral (DAA) treatment.