Incidence of human papillomavirus (HPV) positive tonsillar carcinoma in Stockholm, Sweden: an epidemic of viral-induced carcinoma?

In the county of Stockholm, between 1970 and 2002, we have previously reported a 3-fold parallel increase in the incidence of tonsillar squamous cell carcinoma (SCC) and the proportion of human papillomavirus (HPV) positive tonsillar SCC. Here, we have followed the above parameters in all patients (n = 120) diagnosed with tonsillar SCC during 2003-2007 in the same area, and also in correlation to our previous data. Ninety-eight pretreatment biopsies were available and presence of HPV DNA and HPV-16 E6 and E7 RNA were tested by polymerase chain reaction (PCR) and RT-PCR. Incidence data were obtained from the Swedish Cancer Registry. Data reported from 1970 to 2002 were also obtained for comparison. HPV DNA was present in 83 of 98 (85%) of the tonsillar SCC biopsies from 2003 to 2007 and 77 of these were HPV-16 positive. HPV-16 E6 and E7 RNA were found in 98% of 52 analyzed HPV-16 positive 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% confidence interval (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 and 2007, in parallel with a decline of HPV-negative tumors. In conclusion, the incidence of HPV-positive cancers is still increasing in the County of Stockholm, suggesting an epidemic of a virus-induced carcinoma, with soon practically all tonsillar SCC being HPV positive, as in cervical cancer.