To investigate if polyomavirus infection during pregnancy is linked to development of neuroblastoma in the child, serum samples of 115 index mothers from the pregnancy where the child eventually developed neuroblastoma were identified and matched with serum samples from 8 control mothers per index mother. The samples were tested for specific IgG and IgM antibodies to BK and JC virus using enzyme immunoassays based on purified yeastexpressed virus-like particles (VLPs). The serum samples as well as 10 neuroblastoma cell lines were also analyzed using Real Time (TaqMan) PCR for detection and quantification of BK virus DNA. The BK virus IgG seroprevalence was similar among index mothers (80%) and control mothers (83%) [OR 0.8; 95% confidence interval (95% CI): 0.5-1.3]. BK virus IgM was also not associated with neuroblastoma risk (OR was OR ؍ 0.6 ; 95% with CI, 0.2-1.9). Also JC virus had no association, neither for IgG (OR ؍ 0.9; 95% CI, 0.6 -1.4) nor for IgM (OR ؍ 0.9 ; 95% CI, 0.4 -1.9). All serum samples and all neuroblastoma cell lines were negative for BKV DNA. In summary, a comprehensive cohort using both serology and polyomavirus DNA detection found no evidence for association between BKV or JCV polyomaviruses and neuroblastoma.Key words: neuroblastoma; polyomaviruses; BK virus; JC virus; seroprevalence; maternal infection; virus like particles (VLPs); enzyme immunoassay; Real Time PCR The human polyomaviruses BK and JC can transform human cells in vitro. 1 The virally encoded T antigens of both BKV and JCV are essential for transformation and have been shown to bind the p53 and pRb tumor suppressor proteins. 2,3 BKV infection has also been reported to induce chromosomal aberrations in human cells. 4 The DNA of JCV has been detected in certain brain tumours: in particular oligoastrocytoma. 5 There are also reports of presence of the simian polyomavirus SV40 in several human tumours, including choroid plexus tumours and ependymomas. 5-8 BKV has been detected in a variety of tumours, the most thorough studies being those on neuroblastoma. 9 Neuroblastomas account for 7-10% of all childhood cancers and it is the most common cancer diagnosed during infancy. Neuroblastoma probably derives from primitive sympathetic neural precursors and about half of all neuroblastomas arise in the adrenal medulla. 10 Flaegstad et al. 9 found BKV DNA in 18/18 neuroblastomas by PCR but in 0/5 control adrenals; 16/18 neuroblastomas were also found to contain the virus DNA in the tumor cells by in situ hybridization, and the viral large T antigen was demonstrated by both immunoprecipitation and immunohistochemistry of the tumor cells. JCV and SV40 were not found and all 9 PCR amplimers that were sequenced were confirmed to be BKV DNA. 4,9 The BK-encoded large T antigen was found to bind p53, leading to an aberrant cytoplasmic localization of p53, suggesting a possible transforming mechanism for BKV in neuroblastomas in children. 11 Both BK and JC virus infect a large proportion of children all over the world. Following primar...