In the Stockholm cohort, in a Cox multivariate analysis adjusted for age, gender, stage, and treatment, the researchers found a similar significant rise in relative 5-year survival, with a relative hazard ratio of 0.54 for 1990–2001, compared with 1970–1979. A lower proportion of stage I and II tumors in the ′90s, compared with the ′70s, suggests the improvement in survival over the years can't be explained by earlier diagnosis, Dr. Dahlstrand said.
Finally, when the investigators looked at survival by HPV status in the Stockholm cohort, they found that independent of age, gender, and tumor stage, the hazard ratio for patients with HPV-positive tumors was 0.17.
In all, 49% of cases from 1973 to 2008 were HPV positive, and the E6 and/or E7 mRNA were found in 94% of assessable HPV-positive samples, Dr. Dahlstrand noted.
The findings show that about a threefold increase in the incidence of tonsillar cancer was accompanied by about a threefold rise in the rate of HPV-positive tonsillar cancers. The presence of the E6 and E7 oncogenes provides further evidence linking HPV to tonsillar cancers, she said.
The study funding source was not provided. Dr. Dahlstrand said she has no relevant financial disclosures.