Viral load of HPV in esophageal squamous cell carcinoma

We previously reported the presence of HPV DNA in esophageal squamous cell carcinoma (ESCC) cases from Hong Kong and Sichuan. The role of HPV in the carcinogenesis of ESCC remains unclear, partly due to the large variations in infection rates reported by different studies. While some of these variations may truly reflect different HPV infection rates in ESCC among different geographic regions, differences in sensitivity and specificity of the detection methods used also contribute. In the present study, we used quantitative real-time PCR to determine the copy numbers of HPV-16 and HPV-18 in ESCC from 5 different regions of China with different incidence rates of ESCC. Conforming to our previous reports, HPV infection was detected in 2-22.2% of samples. Infection with HPV-16 was again shown to be more common than that with HPV-18 among Chinese ESCC patients. The copy number of HPV-16 in these ESCC cases ranged from < or =1 to 157 copies/genome equivalent, with 65% of samples harboring fewer than 10 copies/genome equivalent. The median copy number of HPV-18 was 4.9/genome equivalent. Assays were validated using cervical carcinoma cell lines with known copy numbers of HPV-16 or HPV-18. The relatively low HPV copy number and infection rate in ESCC suggest that HPV is unlikely to play as essential a role in the carcinogenesis of ESCC as in cervical cancer. However, with the consistent detection of oncogenic HPVs in ESCC from some regions of China, the possibility of HPV infection being one of the multiple risk factors of ESCC in some geographic areas cannot be excluded.