HPV and base of tongue cancer: Reason for the increased incidence?

Abstract

e16014 Background: We have earlier shown an increase in the incidence of tonsillar cancer and the role of HPV as a risk factor. HPV prevalence in tonsillar cancer is approaching the same numbers as cervical cancer, where almost all tumors are HPV-associated. The second most common cancer of the oropharynx, base of tongue cancer, is not as well investigated regarding incidence trends and HPV prevalence. Following our previous research on tonsillar cancer, we assessed the increase in incidence of base of tongue cancer and the prevalence of HPV in this disease. Methods: Incidence data for base of tongue cancer in Sweden from 1970 to 2007 was obtained from the Swedish Cancer Registry. All patients diagnosed with base of tongue cancer in Stockholm County between 1998-2007 (109 individuals) were identified. From 95 patients, paraffin-embedded, pretreatment biopsies 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. Results: We found an overall increase in the incidence of base of tongue cancer from 0.15/100,000 person years 1970-1974 to 0.47/100,000 person years during 2005-2007 in Sweden. From 1998 to 2007, the prevalence of HPV in base of tongue cancer increased from 58% 1998-2001 to 84% 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. No age difference was observed in HPV-positive and HPV-negative groups, respectively. Conclusions: The incidence of base of tongue cancer is increasing and today over 80% of all base of tongue SCC in the County of Stockholm is HPV positive, which mimics the development for tonsillar cancer in the Stockholm area. This suggests that HPV contributes to the increase of the incidence. There are differences between tonsillar and base of tongue cancer patient, no age difference could be observed between HPV positive and HPV negative patients in the base of tongue group. If, in parallel with tonsillar cancer, this results in better prognosis for patients with HPV-positive base of tongue cancer as compared to patients with HPV-negative cancer, remains to be investigated. No significant financial relationships to disclose.