Toxoplasma Gondii Infection May Be Tied To Higher Risk Of Brain Cancer

Data from two prospective studies point to an association between Toxoplasma gondii infection and the risk of glioma in adults, suggesting that reducing exposure could provide an avenue to modify glioma risk, the researchers say.

"Ours is the first study to show an association between toxoplasma gondii antibodies in the blood (indicating prior infection) and subsequent development of glioma," Dr. Kathleen M. Egan of Moffitt Cancer Center, in Tampa, Florida, told Reuters Health by email.

T. gondii is a common parasite most often acquired from eating undercooked meat. It shows affinity to brain tissue and may lead to the formation of cysts in the brain.

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Prior epidemiologic studies have suggested an association between glioma and increased prevalence of T. gondii infection, but prospective studies are lacking, the study team explains in the International Journal of Cancer.

Using a nested case-control study design, they studied the association between T. gondii antibodies and risk of glioma in two prospective cohorts - the American Cancer Society's Cancer Prevention Study-II (CPS-II) Nutrition Cohort (37 glioma cases and 74 controls) and the Norwegian Cancer Registry's Janus Serum Bank (323 cases and 323 controls).

In both cohorts, a "suggestive increase" in glioma risk was observed in adults infected with T. gondii. For the CPS-II cohort, the odds ratio was 2.70 (95% confidence interval, 0.96 to 7.62) and for Janus it was 1.32 (95% CI, 0.85 to 2.07).

The association was particularly evident among adults with high antibody titers specific to the T. gondii surface antigen sag-1 (OR, 3.35; 95% CI, 0.99 to 11.38 for CPS-II and 1.79; 95% CI, 1.02 to 3.14 for Janus).

"The hypothesis that Toxoplasma gondii might be risk factor for glioma was first raised in studies that suggested higher rates of brain tumors in areas where the parasite was endemic," Dr. Egan said. "That was followed by a few small epidemiologic studies that seem to support a link."

"Researchers were interested in the question because the parasite is tropic to the brain and infection has been linked to a spectrum of neurological problems which raised concern about a possible link to brain tumors," she added.

Dr. Egan cautioned that "larger prospective studies are needed to validate the finding. Should the findings be confirmed, avoidance of exposure to Toxoplasma gondii offers a way to lower risk of glioma. This is important because there are few avenues to reduce risk of these aggressive tumors."

—Megan Brooks

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