A Contemporary Systematic Review on Repartition of HPV-Positivity in Oropharyngeal Cancer Worldwide

Significant variation in human papillomavirus (HPV) prevalence in oropharyngeal squamous cell carcinoma (OPSCC) across countries ranging from 11% in Brazil to 74% in New Zealand has been reported earlier. The aim of this study was to systematically review the most recently published studies on the occurrence of HPV in OPSCC globally. PubMed and Embase were systematically searched for articles assessing the occurrence of HPV+ OPSCC published between January 2016 and May 2021. Studies with a study period including 2015 and the following years were included. Both HPV DNA and/or p16 were accepted as indicators of HPV+ OPSCC. 31 studies were enrolled comprising 49,564 patients with OPSCC (range 12–42,024 patients per study) from 26 different countries covering all continents. The lowest occurrences of HPV+ OPSCC were observed in India (0%) and Spain (10%) and the highest occurrences were observed in Lebanon (85%) and Sweden (70%). We observed great variation in HPV prevalence in OPSCC worldwide varying from 0% to 85%. The highest occurrences of HPV+ OPSCC were found in general in Northern European countries, USA, Lebanon, China, and South Korea. We observed a trend of increase in HPV-positivity, indicating a mounting burden of HPV+ OPSCC.


Introduction
The global burden of oropharyngeal squamous cell carcinoma (OPSCC) is estimated to be approximately 93,000 new patients per year [1]. For the last decades, the incidence of OPSCC has been increasing due to an increase in human papillomavirus-positive (HPV+) OPSCC [2].
p16 is often overexpressed in HPV+ OPSCCs and can therefore be used as a surrogate marker for infection with active HPV, but double positivity for p16 by immunohistochem-2 of 12 istry (IHC) and HPV DNA has shown better prognostication [8,9]. However, there is a remarkable variation in detection methods of HPV+ OPSCC across studies [10,11].
Significant variation in HPV prevalence in OPSCC across countries with HPV positivity ranging from 11% in Brazil to 74% in New Zealand has been reported earlier [10]. It is important to better characterize the current influence of HPV+ OPSCC globally to provide useful information for clinicians and to expand and design the HPV vaccination programs to prevent HPV+ OPSCC at a global level. The aim of this study was to systematically review the most recently published studies on the HPV prevalence in OPSCC worldwide.

Search Strategy and Data Extraction
In May 2021, one author (ALC) systematically searched PubMed and Embase for articles assessing the prevalence of HPV+ OPSCC published between January 2016 and May 2021. Studies with a study period including 2015 and the following years were enrolled. Only studies with data regarding HPV status and with a minimum of five cases were included. Studies evaluating the HPV prevalence in specific subpopulations stratified by gender, comorbidities, or ethnicity were excluded. Both HPV DNA and/or p16 were considered as indicators of HPV+ OPSCC.
The following search strategy was used when searching PubMed: (Oropharyn* cancer or oropharyn* neoplasm or oropharyn* carcinoma or oropharyn* malignancy or oropharyn* tumour or oropharyn* tumor) AND (HPV or human papillomavirus or human papilloma virus or papillomaviridae) AND (incidence or frequency or prevalence). MeSH terms were included as well: Papillomaviridae, neoplasm, carcinoma, incidence, and prevalence. The search was limited to the English language and articles published between January 2016 and May 2021.
The same keywords were used to create three different searches in Embase, which were combined with "AND". The searches were restricted to English language, human studies, and articles published between 2016-2021:

1.
HPV or human papillomavirus or human papilloma virus 2.
Incidence or frequency or prevalence The subsequent parameters were evaluated and extracted from the studies: anatomical sublocation, HPV status, definition of HP-positivity, HPV genotypes, smoking, TNM-stage, age, and sex.

Data Analysis
The occurrences of HPV+ OPSCC were expressed as relative frequencies. A proportion meta-analysis was made to evaluate the overall pooled HPV prevalence and heterogeneity between studies in relation to study size. A random-effect model was considered due to high heterogeneity, with an I2 test value >75% and many small sample sizes. Statistics were performed in RStudio using the packages "metafor", "meta", and "forestplot".

Results
The PubMed and Embase search generated a total of 1697 studies, Figure 1. Thirty-one studies met the inclusion criteria comprising 49,564 patients with OPSCC representing 26 different countries covering South America, the USA, Africa, The Middle East, Asian-Pacific, and Europe.

Global Burden of HPV+ OPSCC
The study population varied from 12 in a study from Ghana [12] to 42,024 in the USA [13], Table 1. Most of the minor studies were observed in Middle Eastern and African countries (n = 12-34). HPV-positivity varied from 0% in India [14] to 85% in Lebanon [15]. Both high and low HPV prevalence were observed across all geographical areas, Table 1.
More than 100 countries have introduced the HPV vaccine in vaccination programs, but primarily to prevent cervical cancer, and is, therefore, most offered to young girls alone [44]. To reach herd immunity, more than 80% HPV vaccine coverage amongst girls is needed, but gender-neutral vaccination programs have proven to be more robust in reaching stable high HPV vaccine coverage protecting both females and males [45][46][47]. Several countries have included young boys in the HPV vaccine programs, e.g., North America, Denmark, Netherlands, and the UK. The 9-valent vaccine covers most of the HR-HPV genotypes causing HPV+ OPSCC globally observed in this review, including HPV16, HPV18, and HPV33 but not HPV35.
The lack of consensus on how to detect HPV was striking, and only 15 studies used double positivity based on both p16 and HPV DNA [4,16,19,20,22,23,28,30,[32][33][34][35][38][39][40], and one study was based on both HPV DNA and HPV RNA [37] (n = 6723) to define HPV+ OPSCC. It has been shown that evaluating only p16 overexpression or HPV DNA has a lower specificity compared to the combination of the two [48]. Incongruence between p16+ and HPV+ has been revealed and can result in false-positive or false-negative results. HPV+/p16-OPSCC might be due to a HPV bystander infection and not a HPV+ cancer, while on the other hand, HPV-/p16+ OPSCC may be caused by genetic alterations and not active HPV infection. But both high and low HPV prevalence were seen regardless of the detection method used.
Most of the studies using p16 ICH defined p16-posititivity according to ASCO guidelines with >70% staining (n = 2663). Four studies defined p16+ as ≥75% staining (n = 2678) [4,22,31,32], while one study defined p16+ as less, ≥10% staining (n = 30) [30]. The largest study enrolled, comprising 42,924 patients from the USA, did not report how they defined HPV+ OPSCC [13]. Mariz et al. has also recently showed discrepancies in the definition of p16-positivity in a systematic review [10]. In order to assess the global burden of HPV+ OPSCC and to compare studies, it is important to align HPV detection methods to identify true, active HPV-infection in OPSCCs.
This review was based on data from a very heterogeneous population of studies derived from different countries, with varying health systems and with different burdens of smoking and alcohol consumption. There was great variety in how the studies reported anatomical subsites within the oropharynx and HPV detection methods. Additionally, there was great variation in the study sizes 024) and with a tendency towards small study populations from countries with a previously less described impact of HPV in OPSCC, e.g., African and Middle Eastern countries (n = 12-34), whereas studies from Europe and the USA were greater in size (n = 22-42,024). These differences may influence the distribution of HPV+ OPSCC observed. Bigger studies from especially African and Middle Eastern countries are needed to further address the burden of HPV+ OPSCC in these geographical areas.
To our knowledge, this is the biggest systematic review on the global burden of HPV+ OPSCC including geographical areas, that have not previously been described in a systematic review. We observed a pooled burden of HPV+ OPSCC of 33% (95% CI 25-40%) globally and, to our knowledge, the so far described highest occurrence of HPV+ OPSCC of 86% in Lebanon.

Conclusions
In conclusion, in this systematic review, we observed great variation in the prevalence of HPV+ OPSCC worldwide, i.e., varying from 0% in India to 86% in Lebanon among 31 enrolled studies comprising 49,564 patients from 26 countries. In numerous studies, an increase in HPV prevalence was observed over time, indicating an increasing burden of HPV+ OPSCC worldwide. HPV16 was the predominant genotype, but also HPV18, 33, and 35 were frequent. HPV16, 18, and 33 are covered by the 9v HPV vaccine. Inconsistencies in HPV detection methods observed emphasize the need for a more uniform definition of HPV positivity. Funding: Amanda-Louise Fenger Carlander was funded by Candys Foundation (2.785.000 DKkr). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Institutional Review Board Statement: Not applicable.