Frequency of HPV-associated tonsillar cancer in Sweden

Abstract

6030 Background: Numerous studies has shown an increase of the incidence of tonsillar squamous cell carcinoma (SCC) both in the USA and in Sweden. This increase in incidence is despite a decreasing prevalence in smoking, a well-known risk factor for developing tonsillar cancer. The proportion of human papillomavirus (HPV) positive tonsillar SCC has also been shown to increase. This study aims to examine the incidence of tonsillar SCC and the proportion of HPV positive tonsillar SCC between 2003–2007 in the County of Stockholm, Sweden in correlation to data from 1970–2002. Methods: All patients (n = 120) diagnosed with tonsillar SCC during 2003–2007 in the County of Stockholm were included in this study. Ninety-eight pre-treatment biopsies were available and presence of HPV DNA and HPV-16 E6 and E7 mRNA were tested by PCR and RT-PCR. Incidence data between 2003–2007 for Sweden and in the County of Stockholm was obtained from the Swedish Cancer Registry. Data reported from 1970 to 2002 was also obtained for comparison. Results: HPV DNA was present in 83/98 (85%) of the tonsillar SCC biopsies from 2003–2007. Of the 77 HPV-16 positive tumors, HPV-16 E6 and E7 mRNA were found in 98% of the analyzed cases. The proportion of HPV-positive cancers had significantly increased both from 1970 to 2007 (p < 0.0001) as well from 2000 to 2007 (p < 0.01), with 68% (95% CI, 53–81) 2000–2002; 77% (95% CI, 63–87) 2003–2005; and 93% (95% CI, 82–99) 2006–2007. The incidence rate of HPV-positive tumors almost doubled each decade between 1970–2007, in parallel with a decline of HPV-negative tumors. Conclusions: Today, almost all tonsillar SCC in the County of Stockholm is HPV positive, and the incidence of HPV-positive cancers is still increasing. The data suggest that we are dealing with an epidemic of a virus-induced carcinoma, and that soon practically all tonsillar SCC will be HPV positive; a similar situation observed in cervical cancer. No significant financial relationships to disclose.