VoPham T, et al. - Given circadian misalignment may increase the risk of developing hepatocellular carcinoma (HCC), researchers assessed the link between distance from time zone meridian, a proxy for circadian misalignment, and HCC risk in the U.S. adjusting for known HCC risk factors. Hepatocarcinogenesis may be influenced by circadian misalignment from residing in the western region of a time zone. In other words, circadian misalignment may be an independent risk factor for HCC.

• Using Surveillance, Epidemiology, and End Results (SEER), researchers obtained information on 56,347 HCC cases diagnosed between 2000 and 2014 from 16 population-based cancer registries in the U.S.
• Using the location of each SEER county's Center of Population in a geographic information system (GIS), estimation of distance from time zone meridian was carried out.
• Incidence rate ratios (IRRs) and 95% confidence intervals (CIs) for the link between distance from time zone meridian and HCC risk were calculated using Poisson regression with robust variance estimation, after adjusting for individual-level age at diagnosis, sex, race/ethnicity, year of diagnosis, SEER registry, and county-level prevalence of health conditions, lifestyle factors, shift work occupation, socioeconomic status, and demographic and environmental factors.

• A 5 degree increase in longitude moving east to west within a time zone was shown to be related to a statistically significant increased risk for HCC (IRR 1.07, 95% CI 1.01-1.14, p=0.03).
• Those <65 years old showed a statistically significant positive association.
• Researchers found no association among individuals ≥65 years old (p for interaction < 0.01).