Mesothelioma Articles

Reuters Health
Posting Date: April 1, 2003 NEW YORK Apr 01, 2003 (Reuters Health) - Poliovirus vaccines that were contaminated with simian virus 40 (SV40) and administered between 1955 and 1961 were not associated with increased cancer incidence, according to a population-based study in Denmark that included nearly 70 million person-years of follow-up. Early poliovirus vaccines were produced in monkey kidney tissue harboring SV40. There has been concern that this contamination may have caused cancer because the SV40 genome encodes a protein that blocks tumor suppressor proteins and because some laboratories have reported SV40 DNA sequences in human tumors. The contamination was eliminated from vaccines released in 1963 and thereafter. Dr. Eric A. Engels, of the National Cancer Institute in Rockville, Maryland, and colleagues chose to study cancer incidence data collected from the Danish Cancer Registry because of the highly efficient campaign to vaccinate Danish children beginning in 1955. They note in the Journal of the National Cancer Institute for April 2 that there was "close to 100% vaccination coverage in the targeted age groups." They found that, by 1997, the incidence of cancer was actually lower among infants or children exposed to contaminated poliovirus, with an age-adjusted relative risk of 0.82 compared with unexposed individuals born between 1964 and 1970 (p < 0.001). For brain and nervous system tumors, the relative risk for those born between 1946 and 1952 (exposed as children) and those born between 1955 and 1961 (exposed in infancy), the relative risk was 0.78 (p < 0.001). Because SV40 is most tumorigenic in newborn laboratory animals, Dr. Engels' team specifically examined overall cancer incidence among children who received contaminated inoculations up to 4 years of age. Here again, the relative risks were significantly higher for all cancers among the last birth cohort. The authors note an observed increase in ependymoma incidence in children inoculated between birth and the age of 4 with the contaminated vaccine than in the preceding unexposed cohort. However, the incidence of ependymoma did not decline in the post-exposure period, peaking in 1969, long after vaccine was cleared of SV40 contamination. Longer term follow-up showed no significant difference in risk between cohorts. "On balance, these results do not suggest an effect of SV40 on ependymoma risk," the authors maintain. "Our population-based, retrospective follow-up study does not support the hypothesis that SV40 is a cause of human cancer." "These data should be very reassuring for adults who were children during the early years of polio vaccination programs," Dr. Engels told Reuters Health. "They point to the fact that 35 years after widespread exposure to a potential cancer-causing virus, we don't see any increase in cancer risk." He noted that his group's report follows "several other well-conducted epidemiological studies" showing similar findings. "I think that field of evidence is solid now and is reaching its conclusion." However, he added, "A number of labs have reported the presence of SV40 DNA in tumors from people with cancer, but some researchers don't find these sequences in the same types of tumors. We just don't know how to interpret those conflicting pieces of evidence, so more research will be necessary." SOURCE:
" Journal of the National Cancer Institute 2003;95:532-539

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