Time trends in pharyngeal cancer incidence in Norway 1981-2005: a subsite analysis based on a reabstraction and recoding of registered cases

Objective Incidence rates of oropharyngeal squamous cell carcinoma (SCC) have been reported to be increasing in several countries in recent decades, contrasting with trends of SCCs diagnosed in neighboring anatomical sites. We investigated whether changes in classification systems and/or coding/registration practices might explain the trends in Norway, focusing on changes in oropharyngeal cancer. Methods Trends in cancers of the oropharynx, base of tongue, nasopharynx, hypopharynx were graphically presented for the period 1981-2005, before and after recoding. Age-period-cohort and future prediction models were fitted to oropharyngeal SCC incidence. Results A total of 85 (3.7%) of the 2315 pharyngeal cancers required recoding. Rates of oropharyngeal cancer in Norway were consistently two to three times higher in men, with rapid increases in both men (5% per annum) and women (4.2% per annum). Assuming generational effects, male cohorts born 1915-1950 were at increasingly higher risk of the disease. The number of oropharyngeal cancer cases is expected to double in Norway by 2020. Conclusions The trends were not considered materially biased by potential artefacts. The increasingly higher proportion of oropharyngeal SCC cancers is more likely explained by other factors, including an increasing high-risk HPV prevalence among recent cohorts. These results will likely have consequences on treatment and health care provision in the near future.