Systematic analysis of human oncogenic viruses in colon cancer revealed EBV latency in lymphoid infiltrates

Abstract

Background: Environmental factors may play a role in colon cancer. In this view, several studies investigated tumor samples for the presence of various viral DNA with conflicting results.

Findings: We undertook a systematic DNA analysis of 44 consecutive, prospectively collected primary tumor samples by real time and qualitative PCR for viruses of known or potential oncogenic role in humans, including polyomavirus (JCV, BKV, Merkel cell polyomavirus), HPV, HTLV, HHV-8 and EBV. Negative controls consisted of surgical resection margins. No evidence of genomic DNA fragments from tested virus were detected, except for EBV, which was found in a significant portion of tumors (23/44, 52%). Real-time PCR showed that EBV DNA was present at a highly variable content (median 258 copies in 10(5) cells, range 15-4837). Presence of EBV DNA had a trend to be associated with high lymphocyte infiltration (p = 0.06, χ2 test), and in situ hybridization with EBER1-2 probes revealed latency in a fraction of these lymphoid cells, with just a few scattered plasma cells positive for BZLF-1, an immediate early protein expressed during lytic replication. LMP-1 expression was undetectable by immunohistochemistry.

Conclusions: These results argue against a significant involvement of the tested oncogenic viruses in established colon cancer.

Keywords: Colon cancer; EBV; Oncogenic viruses.

Figure 1

EBV latency is restricted to the inflammatory infiltrate in colon cancer. Tissue RNA in situ hybridization using EBER 1–2 PNA probes to detect EBV latency (Dako, Denmark). A blue nuclear staining indicates a positive reaction. Epithelial and cancer cells are negative, whereas occasionally positivity of non-neoplastic lymphoid cells may be extensive (reaching 20%).

Figure 2

EBV lytic phase was limited to a few scatter plasma cells in the lymphoid infiltrate. Immunohistochemistry with a monoclonal antibody specific for the early immediate protein BZLF-1. These findings confirmed that EBV is essentially in latency phase in the lymphoid infiltrates of colorectal cancers.