Clinico-pathological features of oropharyngeal squamous cell carcinomas in Malaysia with reference to HPV infection

The profile of head and neck squamous cell carcinoma (SCC) has changed over the past few decades with increased rates of oropharyngeal SCC (OPSCC) having been documented in Europe and the USA [1]. Although risk factors such as tobacco and alcohol consumption are still important for the development of OPSCC, it has become apparent that oncogenic human papillomavirus (HPV) is also an important aetiological agent [2]. HPV is thought to account for the relatively recent increase in OPSCC, with data from Sweden and the USA indicating that 70–80% of OPSCC are HPV positive [3, 4]. Patients with HPV positive tumours are typically non-smokers and have a low consumption of alcohol. Sexual behaviour, such as early age of sexual debut and increasing numbers of sex partners appears to correlate with HPV-related OPSCC [5, 6]. Furthermore, HPV-related OPSCC patients have better survival rates than those with HPV negative tumours [6–12].

p16 immunohistochemistry is used clinically as a surrogate marker for oncogenic HPV infection in OPSCCs and in 2017 UICC and AJCC TNM8 classification assigned p16 positive OPSCC a separate staging system [13]. In developed countries, routine testing for p16 is now recommended for all patients with OPSCC as well as those with metastatic SCC of unknown primary in the head and neck region [14, 15].

At this point in time, there is a lack of accurate epidemiological and clinico-pathological data on the burden of HPV-related OPSCC in Malaysia, as reported by the HPV Information Centre [16]. Two previous studies on HPV-related HNSCCs in Malaysian patients were performed on mostly oral SCC specimens and as such are not representative of the burden of HPV-related OPSCC in Malaysia [17, 18]. Therefore, the aim of this study was to measure the proportion of Malaysian patients with p16 positive OPSCC and to examine the clinico-pathological features.

In previous years, SCCs of the oral cavity and oropharynx were often grouped together and thought of as being a single disease entity [22]. However, this has changed in recent years due to the recognition of HPV as a major aetiopathogenic agent in a subset of OPSCC. HPV positive OPSCC is now recognised as a clinico-pathologically unique form of HNSCC with distinct demographic, clinical and morphological features, as well as being associated with improved clinical outcomes [7, 23–26]. These findings have prompted the changes to oropharyngeal tumours in the 2017 edition of the WHO Classification of Head and Neck Tumours. The new edition has divided tumours of the oral cavity and oropharynx into different chapters and has also sub-classified OPSCC according to HPV status [27]. Furthermore, the UICC and AJCC have recently recommended new clinical and pathological staging systems for p16 positive OPSCC, which reflects the improved prognosis of the disease [13, 28].

The prevalence of p16 positive OPSCC in the Malaysian cohort was half that of a matched UK cohort (25% vs. 49%). The matched UK cohort was representative of a larger (n = 1529) multicentre prevalence study carried out in the UK demonstrating that OPSCC had a p16 positive rate of 54% [29]. Higher rates have also been reported elsewhere in Europe and America (35% vs 80%) [1]. A recent meta-analysis looking at the burden of HPV related head and neck cancers in the Asia Pacific region reported an overall prevalence of 40.53% for oropharyngeal cancers [30]. However, there were considerable differences in the rates between regions and countries; the region with the highest prevalence was Oceania (49.32%) and the country with the lowest prevalence was China (9.50%) [30]. Our findings taken for cases diagnosed between 2009 and 2015 (35%) are comparable to the reported rates in East and South Asian regions (25.8 and 38.7% respectively) and Singapore (42%) [31]. In the present study, 80% of the p16 positive cases were from patients of Chinese ethnicity, whilst all the Indian patients had p16 negative OPSCC. This finding could be particularly relevant because according to the 2010 Population and Housing Census of Malaysia, the Chinese account for only 24.6% of the total population [32]. Although this potentially alarming finding needs to be confirmed in a larger cohort, further research specifically into risk factors that predispose to HPV infection in the oropharynx are warranted in different populations.

Most epidemiological and clinical studies have indicated that patients with HPV positive OPSCC are relatively younger than patients with HPV negative disease [6, 30, 33–35], although our findings do concur with those studies with the mean age of HPV positive patients being slightly lower than the mean age of HPV negative patients, the finding was not statistically significant. According to the recent meta-analysis by Shaikh et al. [30], the prevalence of HPV associated head and neck cancer is higher amongst males, however the studies involved in the meta-analysis involved small study samples as well as unequal gender distributions [30]. The findings from our study are also similar with the findings of the meta-analysis with a slight male predilection.

The recent WHO 2017 edition has discouraged histologic grading of HPV positive OPSCC as there is insufficient evidence to correlate histopathological grading with clinical behaviour and outcomes [27]. All the cases in our study were diagnosed well before the release of the new WHO guideline and were based on previous guidelines that grouped oropharyngeal SCCs with oral cavity SCCs. The majority of HPV positive cases were graded as being poorly differentiated SCCs (70%). This “high grade” histopathologic category was probably based on the non-keratinized, immature and basaloid appearance of the tumour cells. However, such grading may not be accurate as HPV positive OPSCCs mostly arise from the epithelial lining of the tonsillar crypts and therefore retain the non-keratinizing and basaloid appearance of this epithelium.

The disparity between p16 positive rates (25%) and the detection of HR-HPV DNA (17%) is a consequence of the low sensitivity of HR-HPV DNA in situ hybridisation, which has been reported previously [36]. The relatively high rate of p16 positive, high risk HPV DNA ISH negative cases (5 of 15) is likely to reflect pre-analytical variables related to tissue fixation, processing and storage conditions. The HPV tests were conducted in an ISO15189:2012 accredited UK pathology laboratory, where such cases represent around 10% of OPSCCs tested [21]. The use of polymerase chain reaction and RNA-based in situ hybridisation has been shown to increase the detection rates and mitigate against false negative results [37].

The results from this study suggest that the occurrence of HPV-related OPSCC in Malaysia may not be as high as those reported in developed nations such as the UK and the USA, but the proportion of OPSCCs that are HPV positive appears to be increasing, particularly in patients of Chinese ethnicity. Further studies will be required to determine how these observations might impact upon Malaysian communities and the national healthcare system in the future.