HPV DNA, E6/E7 mRNA, and p16^INK4a detection in head and neck cancers: a systematic review and meta-analysis

Summary

Background

We aimed to provide updated information about the global estimates of attributable fraction and type distribution of human papillomavirus (HPV) in head and neck squamous cell carcinomas by doing a systematic review and meta-analysis.

Methods

We did a literature search on PubMed to identify studies that used PCR for detection of HPV DNA in head and neck squamous cell carcinomas with information about HPV genotype distribution. We included studies that tested 20 or more biopsies per cancer site and were published between July 15, 1990, and Feb 29, 2012. We collected information about sex, risk factors, HPV detection methods, and biomarkers of potentially HPV-induced carcinogenesis (E6/E7 mRNA and p16^INK4a). If it was not possible to abstract the required information directly from the paper, we contacted the authors. We did a meta-analysis to produce pooled prevalence estimates including a meta-regression to explore sources of heterogeneity.

Findings

148 studies were included, contributing data for 12 163 cases of head and neck squamous cell carcinoma from 44 countries. HPV DNA was detected in 3837 cases. HPV16 accounted for 82·2% (95% CI 77·7–86·4) of all HPV DNA positive cases. By cancer site, pooled HPV DNA prevalence estimates were 45·8% (95% CI 38·9–52·9) for oropharynx, 22·1% (16·4–28·3) for larynx (including hypopharynx), and 24·2% (18·7–30·2) for oral cavity. The percent positivity of p16^INK4a positive cases in HPV-positive oropharyngeal cancer cases was 86·7% (95% CI 79·2–92·9) and of E6/E7 mRNA positive cases was 86·9% (73·2–96·8). The estimate of HPV attributable fraction in oropharyngeal cancer defined by expression of positive cases of E6/E7 mRNA was 39·8% and of p16^INK4a was 39·7%. Of subsites, tonsils (53·9%, 95% CI 46·4–61·3) had the highest HPV DNA prevalence. HPV DNA prevalence varied significantly by anatomical site, geographic region, but not by sex or tobacco or alcohol consumption.

Interpretation

The contribution of HPV prevalence in head and neck squamous cell carcinoma and in particular that of HPV16 in the oropharynx shows the potential benefit of prophylactic vaccines.

Funding

European Commission.

Introduction

In the past decade, an increasing amount of information about the role of human papillomavirus (HPV) in head and neck cancer has been amassed. Nowadays, it is widely accepted that HPV-related head and neck cancers differ substantially from those that are HPV-unrelated—which are mainly caused by tobacco and alcohol—at the genetic, molecular, epidemiological, and clinical level.¹ The resulting increased knowledge has raised some controversies about the accurate proportion of HPV-driven cases, the role of cofactors, and the heterogeneity of HPV prevalence in anatomical sites of the head and neck (oral cavity, oropharynx, and larynx) and across geographical regions. Studies have shown that patients with HPV-related oropharyngeal cancer respond better to treatment and have better survival than patients with HPV-unrelated oropharyngeal cancer.² Moreover, preliminary results from an ongoing randomised trial designed to assess the efficacy of the bivalent vaccine against cervical HPV infections and lesions have shown strong protection conferred by the vaccine against oral infection with HPV16 and HPV18.³

Worldwide, an estimated 599 637 new cases of and 324 794 deaths from head and neck cancer (excluding nasopharyngeal cancer) occur every year.⁴ The epidemiology of head and neck cancer shows sex and regional diversities with most of the cases occurring in men in south central Asia, east Asia, North America, and central eastern Europe, typically attributed to greater tobacco and alcohol consumption.⁴ A recent review estimated that the probability of an HPV-attributable cancer of the oral cavity, larynx, and hypopharynx is at least five times lower than that of oropharyngeal cancer.⁵ An increase in the incidence of oropharyngeal cancer has been noted in several high-income countries during the past two decades6, 7 and also in the proportion of HPV-related oropharyngeal cancer.⁸

In 2005, a systematic review of HPV DNA detection in head and neck squamous cell carcinomas identified 5640 cases from 60 studies from 26 countries.⁹ The review established that HPV16 accounted for most types of HPV detected in all sites, particularly in the oropharynx (86·7% of all HPV DNA positive cases). Substantial regional variations in HPV DNA prevalence were also reported.⁹ However, major gaps remained including little data for Africa, Asia, and Oceania, and important covariates such as sex, tobacco, and alcohol consumption were not taken into account. Differences between PCR methods were not considered. More recent reviews8, 10 provided updated information about HPV prevalence in head and neck squamous cell carcinomas, but analysed neither the distribution of HPV types nor the covariates mentioned above. To the best of our knowledge, no study so far has done a meta-analysis of HPV prevalence in head and neck subsites. Further, to our knowledge, no meta-analyses of HPV DNA prevalence and type distribution have been done presenting additional data for E6/E7 mRNA, a biomarker of HPV viral transcriptional activity, or p16^INK4a, a cell surrogate marker of HPV-induced carcinogenic transformation. The identification of HPV DNA in the tumour does not provide enough evidence for a causal viral association, because the technique cannot differentiate transitory versus oncogenically active infection. The identification of the transcripts of the viral oncogenes E6/E7, implicated in the oncogenic process, through mRNA techniques¹¹ is widely accepted as the present gold-standard test to elucidate the oncogenic role of HPV in the tumour. The use of inmunohistochemical techniques to detect p16^INK4a followed by HPV DNA detection has been also validated to clinically detect an oncogenically active HPV infection in oropharyngeal cancer.¹²

We aim to provide updated information about the global prevalence and type distribution of HPV in head and neck squamous cell carcinomas, by cancer site and by continent, and to assess the proportion of HPV-driven head and neck squamous cell carcinomas by taking into account biomarkers of carcinogenesis such as p16^INK4a and E6/E7 mRNA. Additionally, we explore the role of sex and other cofactors such as tobacco and alcohol consumption and HPV detection methods.