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 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."
Incidence of non-Hodgkin lymphoma has risen through-out the last half of the twentieth century, concurrent with the use and environmental dispersion 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 provide an important clue to the cause of NHL," Rothman said. "However, these associations need to be examined in other studies. If the relationship is consistently replicated, we need to carefully address whether or not PCBs or furans are likely to cause lymphoma, or if another risk factor that is associated with these chemicals could be the true causative agent."
Nearly 54,000 Americans will be diagnosed with non-Hodgkin lymphoma this year, according to the American Cancer Society. More than 19,000 will die from the disease. More men (23 of every 100,000) develop the lymphatic system cancer than women (16 per 100,000). Most non-Hodgkin lymphoma patients are mature adults. The average age at diagnosis is 60 years, with the average survival of patients with low-grade lymphomas about six to eight years after diagnosis. Some 30 percent of patients diagnosed with high-grade lymphomas are permanently cured after treatment, which varies by type of lymphoma and response to chemotherapies.
The De Roos study was the result of collaborations between National Cancer Institute epidemiologists led by Patricia Hartge, Sc.D., the Principal Investigator of the study; along with NCI scientists Jay Lubin, Ph.D., Joanne Colt, M.S. and Rothman at the National Institutes of Health, Department of Health and Human Services. Chemical analysis of the blood components was performed under the guidance of Larry Needham, Jr., Ph.D., with Don Patterson, Ph.D. at the Division of Laboratory Sciences, National Center for Environmental Health, Center for Disease Control and Prevention, Atlanta, Ga.. Also contributing to the study were James Cerhan, M.D., Ph.D., Mayo Clinic College of Medicine, Rochester, Minn.; Rick Severson, Ph.D., Karmanos Cancer Institute, Wayne State University, Detroit, Mich.; and Wendy Cozen, D.O., Keck School of Medicine, University of Southern California, Los Angeles, Calif.
Founded in 1907, the American Association for Cancer Research is a professional society of more than 24,000 laboratory, translational, and clinical scientists engaged in all areas of cancer research in the United States and in more than 60 other countries. AACR's mission is to accelerate the prevention and cure of cancer through research, education, communication, and advocacy. Its principal activities include the publication of five major peer-reviewed scientific journals: Cancer Research; Clinical Cancer Research; Molecular Cancer Therapeutics; Molecular Cancer Research; and Cancer Epidemiology, Biomarkers & Prevention. AACR's Annual Meeting attracts more than 15,000 participants who share new and significant discoveries in the cancer field. Specialty meetings, held throughout the year, focus on the latest developments in all areas of cancer research.