Toxoplasma gondii infection may increase risk for glioma
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Toxoplasma gondii infection appeared to increase the risk for glioma in adults, according to study results published in International Journal of Cancer.
“The hypothesis that T. gondii might be a risk factor for glioma was first raised in studies that suggested higher rates of brain tumors in areas where the parasite was endemic. This was followed by a few small epidemiologic studies that seem to support a link,” Kathleen M. Egan, ScD, researcher in the department of cancer epidemiology at Moffitt Cancer Center, told Healio. “Researchers were interested in the question because the parasite is tropic to the brain and infection has been linked to neurological problems, which all raise concerns about a link with brain tumors. Our study is the first to show an association between T. gondii antibodies in the blood — which indicates prior infection — and subsequent development of glioma.”
T. gondii is a parasitic infection commonly acquired from undercooked meat, and it has the potential to cause cysts in the brain. Previous research has indicated an association between the risk for glioma and an increased prevalence of T. gondii infection; however, prospective data are lacking.
For this reason, Egan and colleagues examined the association of prediagnostic T. gondii antibodies with glioma risk among participants in the American Cancer Society’s Cancer Prevention Study-II Nutrition Cohort (cases, n = 37; controls, n = 74) and the Norwegian Cancer Registry’s Janus Serum Bank (cases, n = 323; controls, n = 323).
About 54% of patients with glioma in the American Cancer Society cohort were women. The mean age at blood draw was 70 years among both cases and controls, and the mean year of blood draw was 2000. In the Norwegian cohort, about 68% of patients with glioma were men, the mean age at blood draw was 40 years and the mean year of blood draw was 1983.
Researchers analyzed blood samples gathered before glioma diagnosis to assess the presence of antibodies to two T. gondii surface antigens and considered those with antibodies to either antigen as seropositive. They used conditional logistic regression to calculate ORs.
Results showed an increased risk for glioma among those with T. gondii infection in both the American Cancer Society cohort (OR = 2.7; 95% CI, 0.96-7.62) and the Norwegian cohort (OR = 1.32; 95% CI, 0.85-2.07). Those with high levels of antibody titers specific to the sag-1 antigen demonstrated the highest risk (American Cancer Society cohort, OR = 3.35; 95% CI, 0.99-11.38; Norwegian cohort, OR = 1.79; 95% CI, 1.02-3.14).
Researchers observed similar positive associations between T. gondii seroprevalence overall and glioblastoma among each cohort (American Cancer Society, OR = 2.31; 95% CI, 0.71-7.47; Norwegian, OR = 1.5 95% CI, 0.83-2.72).
Limitations of the study included the fact that it was not possible to reliably assess T. gondii associations specific to glioma subtype, exposure latency and antibody titer in the American Cancer Society cohort because of the limited sample size. Investigators also could not assess associations by race and ethnicity because most patients in both cohorts were white. In some cases, blood samples were collected years before serologic testing for T. gondii, and long storage time could affect results, according to the researchers.
“Should our findings be confirmed, avoidance of exposure to T. gondii offers a way to lower the risk for glioma. This is important because there are few avenues to reduce the risk for these aggressive tumors. Larger prospective studies are needed to validate our findings,” Egan said.
For more information:
Kathleen M. Egan, ScD, can be reached at Moffitt Cancer Center, 12902 Magnolia Drive, Tampa, FL 33612; email: kathleen.egan@moffitt.org.
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