Beschreibung: Background Glioblastoma multiforme (GBM) is a rare tumor, which affects 1/100 000 individuals, but it represents 30% of central nervous system malignancies. GBM is a severe tumor responsible for 2% of all cancer-related deaths. Although characterized by genotypic and phenotypic heterogeneities, GBM invariably resists conventional chemo- and radiotherapies. Several chromosome alterations and gene mutations were detected in GBM. Simian virus 40 (SV40), a small DNA tumor virus, has been found in GBM specimens by some studies, while other investigations have not confirmed the association. Methods An indirect enzyme-linked immunosorbent assay with 2 synthetic peptides mimicking SV40 antigens of viral capsid proteins 1–3 was employed to detect specific antibodies against SV40 in serum samples from GBM-affected patients, together with controls represented by patients affected by breast cancer and normal subjects of the same median age. Results Our data indicate that in serum samples from GBM-affected patients ( n = 44), the prevalence of antibodies against SV40 viral capsid protein antigens is statistically significantly higher (34%, P = .016 and P = .03) than in the control groups (15%), represented by healthy subjects ( n = 101) and patients affected by breast cancer ( n = 78), respectively. Conclusion Our data indicate that SV40, or a closely related yet undiscovered human polyomavirus, is associated with a subset of GBM and circulates in humans. Our study can be transferred to the clinical oncology application to discriminate different types of heterogeneous GBM, which in turn may address an innovative therapeutic approach to this fatal cancer.