Background and Objective
HPV-related oropharyngeal cancer is increasing rapidly worldwide in both men and women, yet no effective screening strategies currently exist and most patients are diagnosed only after symptoms develop, limiting opportunities for early intervention and prevention. Circulating antibodies to HPV16 E6 oncoprotein are a strong marker of oropharyngeal squamous cell carcinoma (OPSCC). Previously, HPV16-E6 seroconversion was detected 6–28 years before cancer diagnosis but in the present study, we complemented serologic measurements with HPV DNA and RNA genotyping of tumor tissue from the same OPSCC patients. Furthermore, we refined estimates of the timing of—and age at—HPV16-E6 seroconversion preceding HPV-driven OPSCC, and examined whether these estimates vary by key covariates such as tobacco use.
Methods
307 OPSCC cases were identified from the prospective Janus Serum Bank Cohort in Norway  enrolled from 1972 to 2004. Pre-diagnostic samples were analyzed for antibodies against HPV16 and other oncogenic HPV type peptides by multiplex serology. Diagnostic formalin-fixed paraffin-embedded tumor blocks were obtained and HPV DNA and RNA genotyped by Multiplex Papillomavirus Genotyping and HPV type-specific E6*I RNA assays. Cancers positive for DNA and RNA of the same HPV type were regarded as “HPV-driven”. Information about smoking status at time of pre- diagnostic sample was available from questionnaires. For every HPV16-driven cancer, an age and time interval for HPV16-E6 seroconversion was inferred and the Turnbull estimator for interval-censored data was applied. 
Results 
Out of 242 OPSCC cases with a retrieved and successfully sectioned tumor block, 221 (83.7%) had a valid HPV DNA/RNA cancer tissue test. The proportion of OPSCC driven by HPV increased rapidly from 1990 (0%) to 2010 (over 60%). The majority of the HPV-driven OPSCC cases were caused by HPV16 (55.2% of all OPSCC cases), followed by HPV33 (5.4%), HPV18 (0,9%) and HPV35,39,45,59 (0,5%, each). All patients developing HPV16-driven cancer within 10 years from blood draw were HPV16-E6 seropositive. The estimated median age of HPV16-E6 seroconversion for HPV16 driven cancers was 43 years with an interquartile range (IQR) of 41-46, and the median time from seroconversion to HPV16-driven cancer was 16 years (IQR: 12-22). Current smokers had a much shorter time from seroconversion to cancer than former and never smokers (median of 14 vs 18 and 21 years).
Conclusions/Implications.
HPV16-E6–seropositive individuals who were smokers at the time of blood draw developed HPV16-driven OPSCC 8 years earlier than seropositive individuals who never smoked, suggesting a risk-based approach with intensified follow-up of HPV16-E6–seropositive smokers. The estimated age at HPV16-E6 seroconversion suggests that the cancer-causing HPV infection may be acquired after the mid-20s, informing the design and timing of HPV vaccination policies, including catch-up vaccination.