Vidyya Medical News Service
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Exposure to contaminated poliovirus vaccine not likely linked to rare cancer

The poliovirus vaccine used in mass immunization programs in the late 1950s and early 1960s was contaminated with the monkey virus SV40, which has been detected in some human tumors, particularly pleural mesothelioma. However, the rise in incidence of pleural mesothelioma between 1975 and 1997 is not likely the result of immunization with the SV40-contaminated vaccine, according to an analysis in the January 1 issue of the Journal of the National Cancer Institute.

SV40, or simian virus 40, can cause tumors in rodents when injected at high levels. However, most epidemiologic studies of people who were immunized as children with poliovirus vaccine that was potentially contaminated with SV40 have not found an association between SV40-contaminated poliovirus vaccine and the risk of cancer--even more than 30 years after exposure. Still, the presence of SV40 in some tumors raises the possibility that there may be an association.

To determine whether immunization with the contaminated poliovirus vaccine had any affect on the incidence of pleural mesothelioma, a rare cancer of the membrane that covers the lungs, Howard D. Strickler, M.D., of the Albert Einstein College of Medicine in New York, and his colleagues used cancer incidence data from the National Cancer Institute's Surveillance, Epidemiology, and End Results Program to estimate age- and sex-specific incidence rates of pleural mesothelioma from 1975 through 1997. They then compared trends in mesothelioma incidence with prevalence of exposure to SV40-contaminated poliovirus vaccine.

The authors found that incidence rates increased the most among males who were age 75 or older, the age group least likely to have been exposed to the contaminated poliovirus vaccine. Incidence rates among males in the age groups most heavily exposed to SV40-contaminated poliovirus vaccine (between ages 25 and 54) remained stable or decreased from 1975 through 1997.

Similar trends were seen among females. The authors point out that even though women had similar exposure to SV40 contaminated vaccine, female pleural mesothelioma remained very rare, and the few female cases that did occur were mainly among the elderly who were unlikely to have ever received any poliovirus vaccine. In addition, statistical assessment of trends in pleural mesothelioma incidence did not reveal any increases in rates of the disease that could be attributed to SV40-contaminated poliovirus vaccine in males or females.

"Thus, after almost 40 years of follow-up, U.S. cancer incidence data have not shown an increased incidence of pleural mesothelioma among the birth cohorts that were exposed to SV40-contaminated poliovaccine," the authors conclude. However, they note that "continued surveillance of all vaccine-exposed cohorts is needed, in view of conflicting reports on the detection of SV40 genomic DNA sequences in mesothelioma tumor samples."


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