The etiology of mycosis fungoides (MF) remains to be determined. Several studies have proposed a viral etiology with controversial results. In this case-control study we investigated the presence of Epstein-Barr virus (EBV) and the debated presence of Human T-cell lymphotrophic virus I (HTLV-I) sequences, by polymerase chain reaction on nucleic acid extracts from formalin-fixed paraffin-embedded skin biopsies. Moreover, by a multivariate approach we analyzed in the same case-control study also the contribution of two previously examined pathogens: Hepatitis C virus (HCV) and Borrelia burgdorferi (Bb). Significant differences in the frequency of infectious agents in cases and controls were detected for Bb, HTLV-I and EBV. In MF patients we found the concurrent presence of two or three of these pathogen sequences in 21 out of 83 cases, but only in 1 out of 83 healthy controls. Our results suggest that the persistence of multiple infectious agents may cause a long-term antigenic stimulation contributing to the malignant transformation of T lymphocytes, especially when associated with HTLV-I like sequences. However, these infectious agents do not seem to have effects on
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