BENZENE EXPOSURE INCREASE LYMPHOMA RISK

The incidence of non-Hodgkin's lymphoma (NHL) is significantly higher in areas closest to facilities releasing benzene into the environment, according to a new study.

The results, published online July 29 in Cancer, support an association between benzene exposure and the incidence of NHL.

Benzene is an important industrial chemical and is a component of gasoline. Exposure can cause chromosomal aberrations and genetic changes, note lead author Christopher Flowers, MD, associate professor of hematology and medical oncology at Emory University School of Medicine in Atlanta.

Toxic effects can occur at air levels below 1 part per million, suggesting that even low levels of exposure can be harmful. Although benzene exposure has consistently been linked to hematologic cancers, its relation to NHL remains controversial. However, a number of population studies have supported an association between occupational benzene exposure and the risk of developing NHL.

As expected, there was a 0.31% decrease in the risk for NHL for every mile increase in the average distance from a site that releases benzene into the surrounding air or water, such as petroleum refineries and manufacturing plants.

The researchers suggest that benzene exposure is a risk factor for NHL, but currently, there are no direct applications to oncology practice.

However, there are some important take-home messages for oncologists, Dr. Flowers told Medscape Medical News.

"There are associations between residential location and location-related exposure to benzene and the incidence of lymphoma," he said. "This is one of the first studies to look at these relationships."

This study is a first step in identifying risk factors for lymphoma. "Follow-up studies based on these data can ultimately lead to strategies for prevention," Dr. Flowers added.

Prevalent in Urban Areas

The researchers obtained population and demographic data from the 2000 US Census, and identified 12,716 incident cases of NHL from the Georgia Comprehensive Cancer Registry from 1999 to 2008. They obtained geocoded data on benzene release sites from 1988 to 1998 from the Environmental Protection Agency Toxics Release Inventory.

They also obtained age-specific, sex-specific, and race-specific crude incidence rates for NHL, NHL subtypes of B-cell NHL, T-cell NHL, diffuse large B-cell lymphoma, and follicular lymphoma.

The overall annual incidence of NHL in Georgia is low (17.4 per 100,000 population), but the incidence of the disease was significantly higher in areas closer to benzene release sites. Cluster analyses identified several "hot spots" and "cold spots" for NHL and its subtypes throughout the state. The metropolitan Atlanta area was almost always identified as a hot spot; cold spots tended to be in the southern half of Georgia.

The incidence rates of NHL near benzene release sites were higher than expected. Specifically, the incidence was significantly higher surrounding 15 of the 19 benzene release sites, and all benzene release sites located in the greater Atlanta metro area had significant focal clustering.

Only 1 benzene release site associated with an increased incidence of NHL was located outside of metropolitan Atlanta; it was near Savannah.

More Info Needed

Exposure to factors that have not been assessed could be responsible for the increased incidence of NHL in urban areas, the researchers note.

However, neither cigarette smoke nor auto exhaust, both common in urban areas, have consistently been associated with an increased risk for NHL. In addition, pesticides, which are more common in rural areas, have been linked to an increased risk for NHL, they explain.

Future research should "evaluate other potential sources of benzene exposure, other environmental exposures, and genetic and clinical factors that may explain the higher incidence of NHL observed in certain areas," the Dr. Flowers and colleagues conclude.

The study was supported in part by Dr. Flowers' Georgia Cancer Coalition Distinguished Scientist Award, and by a Cancer Research Award, the American Society of Hematology Amos Medical Faculty Development Award, and the National Cancer Institute. The authors have disclosed no relevant financial relationships.

Cancer. Published online July 29, 2013. Abstract