PCBs and Furans May Factor In Risk of Non-Hodgkin's Lymphoma

Scientists have found some additional evidence that environmental exposure to polychlorinated biphenyls (PCBs) may be associated with Non-Hodgkin's lymphoma, according to a study published in the December 1 issue of Cancer Research.

By comparing blood levels of PCBs in 100 pairs of healthy volunteers and non-Hodgkin lymphoma patients, Anneclaire De Roos, Ph.D., assistant professor of epidemiology, Fred Hutchinson Cancer Research Center, and colleagues determined that high levels of three specific molecular forms of PCBs are linked to an increased risk of developing cancer that starts in patients' lymph tissue.

The research also disclosed a potential increased risk of Non-Hodgkin's lymphoma associated with high blood levels of total dibenzofurans. Furans form as a by-product of waste incineration and other industrial processes and are also present in the environment at lower levels than PCBs.

"This study strengthens the hypothesis that persistent organochlorines may be associated with risk of lymphoma" said Nathanial Rothman, a researcher in the National Cancer Institute's Division of Cancer Epidemiology and Genetics.

"The furans are a new hypothesis, and the PCB findings provide us with some additional evidence, but these studies really need to be replicated broadly with much larger numbers of cases. Also, it is important to follow-up these findings in prospective cohort studies that collect blood samples from people when they are healthy, so that we can measure organochlorine levels before their disease develops."

The incidence of Non-Hodgkin's lymphoma has risen through-out the last half of the twentieth century, concurrent with the use of synthetic PCBs. Although their production has been banned for more than 25 years in the United States due to toxicological concerns, PCBs persist in the environment and remain in humans because they break down slowly.

"Though they aren't being produced any more we still detect them in the environment, but at lower levels than in the past," Rothman said.

Nonetheless, the presence of PCBs in the environment and even in the blood of humans doesn't mean that these compounds are cancer-causing substances, he cautioned. "There is still a good deal of uncertainty as to whether PCBs are actually causally associated with any cancer in humans." he said.

While their current report adds more evidence about PCBs and cancer, it was not designed to produce the 'smoking gun' evidence that defines the molecular events induced by cellular exposure to PCBs resulting in initiation of cancer. Also, studies of workers with high occupational exposure to PCBs have not detected an excess of lymphoma, adding uncertainty to the relationship.

"We believe our findings could ...