Texas counties with the highest rates of hepatocellular carcinoma (HCC) diagnoses tended to be those with the highest levels of certain airborne organic chemicals, such as benzene and toluene, known to be human carcinogens, researchers said here.

Although potential confounders were not adjusted for in the analysis, conducted by Ali Shirafkan, MD, and colleagues at the University of Texas Medical Branch in Galveston, Shirafkan told MedPage Todaythat the findings suggest that the association deserves more study to determine whether it may be causative.

A total of 20 such pollutants were significantly elevated in counties with high HCC incidence rates, he reported at the Digestive Disease Week annual meeting. In addition to benzene and toluene, they included other known carcinogens such as hexane, methyl-t-butylether, methyl chloroform, 1-3 butadiene, and 2-2-4 trimethylpentane.

Most of the pollutants identified are effluents from oil and gas extraction and processing.

Shirafkan said the study was motivated by recognition that Texas, in addition to being the nation’s largest oil and gas producer, also has one of the highest rates for HCC, at 9.9 per 100,000 population. The state is also a leading agriculture producer, another industry that exposes many people to chemical pollutants.

As a first look at potential relationships, his group pulled county-level cancer incidence data from the Texas Cancer Registry and several federal data sources, along with county-level pollution data on 188 compounds collected by the U.S. Environmental Protection Agency.

The researchers grouped counties with available data (118 of 254 in the state) into four clusters: one group of 10 that had HCC incidence of zero, one that was primarily agricultural, one comprising the urban centers of Houston, San Antonio, and Dallas-Fort Worth, and a fourth with other urban centers and concentrations of oil/gas extraction and refining. HCC rates in the latter three clusters ranged from 7.48 to 9.45 per 100,000 population.

For the clusters with zero HCC incidence and with agriculture as the dominant industry, there was no association with airborne pollutants, the researchers found. The associations were limited to the two clusters containing urban centers and concentrations of oil/gas facilities.

Shirafkan emphasized that these data did not take into account any potential confounders such as socioeconomic factors, obesity or other comorbidities, or exposures to other types of carcinogens. He readily agreed that air pollution exposure could be a marker for poverty or general poor health, for example. He said he plans to examine such relationships in the next phase of research, and also agreed that extending such analyses to other states would be worthwhile.