Herbal medicine use, Epstein-Barr virus, and risk of nasopharyngeal carcinoma.

Herbal medicine use is thought to be linked to nasopharyngeal carcinoma (NPC) either through its ability to reactivate the Epstein-Barr virus (EBV) or through a direct promoting effect on EBV-transformed cells. To investigate this, 104 histologically confirmed NPC cases and 205 matched controls were studied in The Philippines. Blood was collected to assess antibody titers against EBV, and an interview was administered which elicited information concerning herbal medicine use and other risk factors for NPC. Subjects strongly positive for anti-EBV antibodies (Epstein-Barr nuclear antigen [EBNA]) (titers greater than or equal to 1:80) were at a 21-fold excess risk of disease (95% confidence interval, 8.4, 51.8). Herbal medicine use was also associated with NPC (relative risk, 2.5; 95% confidence interval, 1.4, 4.5). Associations persisted after adjustment for education, smoking, Chinese ancestry, and consumption of salted fish. Exposure to herbal medicines among subjects testing negative/weakly positive for anti-EBNA antibodies was not associated with an elevation in risk (relative risk, 0.6), strong positivity to anti-EBNA antibodies in the absence of herbal medicine use was associated with a significant 16-fold excess risk of disease, and exposure to herbal medicines among subjects testing strongly positive for anti-EBNA antibodies was associated with a significant 49-fold excess risk of NPC when cases were compared to controls. Similar results were obtained when other serological measures of EBV exposure were used. Anti-EBV antibody titers were elevated in herbal medicine users compared to nonusers among cases but not among control subjects. This suggests that, if herbal medicines interact with EBV in the development of NPC, they do not do so by reactivating EBV infection but rather through a direct proliferative effect on EBV-transformed cells. Although the interaction between EBV and herbal medicines is biologically plausible, larger, more detailed studies need to be conducted to validate this preliminary finding.