The role of human papillomavirus in the increased incidence of base of tongue cancer

Numerous reports have shown that the incidence for oropharyngeal cancer is increasing and that human papillomavirus (HPV) is a risk factor. However, few studies have investigated the specific subsites of the oropharynx. Following our previous research on tonsillar cancer, we assessed the increase in the incidence of base of tongue cancer and the prevalence of HPV in this disease. Between 1998 and 2007, 109 patients were diagnosed for base of tongue cancer in Stockholm county. Ninety-five paraffin-embedded diagnostic tumor biopsies from patients were obtained and tested for HPV, both by general HPV PCR and HPV-16/HPV-33 type-specific PCR. Expression of HPV-16 RNA was analyzed to confirm E6 and/or E7 expression. Incidence data were obtained from the Swedish Cancer Registry. An overall increase in the incidence of base of tongue cancer from 0.15/100,000 person-years during 1970-1974 to 0.47/100,000 person-years during 2005-2007 was found in Sweden. The prevalence of HPV in base of tongue cancer in Stockholm county increased from 58% during 1998-2001 to 84% during 2004-2007 (p < 0.05). In the HPV-positive tumors, HPV-16 dominated (86%) but interestingly, HPV33 was detected in as many as 10%. E6 and/or E7 RNA were found in 85% of the samples tested. The incidence of base of tongue cancer, as well as the proportion of HPV-positive tumors, has increased in Sweden during the study period, suggesting that HPV may contribute to this increase.