The underreporting of hepatocellular carcinoma to the cancer register and a log-linear model to estimate a more correct incidence.

The Cancer Register (CR) in Sweden has reported that the incidence of primary liver cancer (PLC) has slowly declined over the last decades. Even though all cancers, irrespective of diagnostic method, should be reported to the CR, the PLC incidence may not reflect the true rate. Improved diagnostic tools have enabled diagnosis of hepatocellular carcinoma based on noninvasive methods without histological verification, possibly associated with missed cancer reports or misclassification in the CR. Our objective was to study the completeness and assess the underreporting of PLC to the CR and to produce a more accurate estimate based on three registers. The CR, the Cause of Death Register, and the Patient Register were investigated. Differences and overlap were examined, the incidence was estimated by merging data from the registers, and the number reported to none of the registers was estimated using a log-linear capture-recapture model. The results show that 98% of the PLCs reported to the CR were histologically verified; 80% were hepatocellular carcinoma and 20% were intrahepatic cholangiocarcinoma. Unspecified liver cancer decreased over time and constituted <10% of all reported liver cancers. The CR may underestimate the liver cancer incidence by 37%-45%, primarily due to missed cancer reports. The estimated annual number of liver cancers increased over time, but the standardized incidence was stable around 11 per 100,000. Hepatitis C-associated liver cancer increased and constituted 20% in 2010. Conclusion: There was an underreporting of PLC diagnosed by noninvasive methods; the incidence was considerably higher than estimated by the CR, with a stable incidence over time; reporting needs to improve and combining registers is recommended when studying incidence.