Correlation of p16 expression and HPV type with survival in oropharyngeal squamous cell cancer
Introduction
Squamous cell carcinoma of the head and neck (HNSCC) accounts for 3% of all new cancer (53,000) diagnoses in the US annually [1]. Epidemiological data from the Surveillance, Epidemiology, and End Results Program (SEER) show that while overall incidence of HNSCC has decreased in conjunction with a decrease in smoking and drinking, oropharyngeal squamous cell cancers (OPSCC) have increased both in the United States and other developed nations internationally [2], [3]. Human papillomavirus is now recognized as an important etiologic factor in OPSCC and the increase in incidence and prevalence of OPSCC is being driven by an increase in HPV associated oropharyngeal cancer over time. HPV16 accounts for 90–95% of HPV positive OPSCC [4], [5], [6], [7], [8]. HPV is also an important prognostic factor, as numerous prospective and retrospective trials have shown that patients with HPV positive OPSCC have a significantly better overall survival than patients with HPV negative OPSCC [9], [10], [11], [12], [13]. P16INK4A (p16) expression assessed through immunohistochemistry (IHC) is increasingly recognized as a reliable surrogate marker for HPV testing [9], [10], [14], [15]. Expression of p16 is increased in HPV infection by HPV E7 oncoprotein inactivation of pRB tumor suppressor, with a resulting loss of p16 suppression.
HPV status and its correlation with p16 IHC in OPSCC varies depending on the molecular test used. HPV DNA in situ hybridization (ISH) has a higher rate of discordance with p16 IHC in reported studies, due to lower sensitivity of HPV DNA ISH compared to HPV DNA PCR testing [13], [16], [17]. HPV RNA in situ hybridization is a novel method of testing; the few studies that have utilized it show an improved correlation compared to DNA ISH [18], [19], [20], [21]. HPV DNA PCR has a high correlation with p16 IHC due to high sensitivity and specificity, with most OPSCC studies reporting a discordance of less than 20% with p16 IHC [22], [23], [24], [25], [26], [27], [28], [29].
The prognostic significance of discordant results has not been elucidated. At least one study has shown that HPV+/p16+ patients have the best outcome, while HPV−/p16+ have an intermediate prognosis compared to HPV−/p16− patients [32]. In another study, patients discordant for HPV and p16 had no disease relapse [30], [31]. It therefore may be clinically important to detect HPV-associated cancers with a test showing the highest correlation between HPV status and p16 IHC.
The purpose of the present study is to correlate p16 expression determined by IHC with HPV16 DNA status determined by E6/E7 DNA PCR and analyze the prognostic significance of the combined marker results. As noted above, HR HPV types other than HPV16 have been reported to account for 5–10% of HPV OPSCC cancers. Therefore we used the Roche LINEAR ARRAY® HPV Genotyping Test (“LAHPV test”; Roche, Indianapolis, USA) to resolve discrepant HPV16 DNA PCR and p16 IHC results. The LAHPV test is capable of detecting 37 high and low risk HPV genotypes, including co-infections, [32] has demonstrated high general and type-specific reproducibility in cervical samples, and has successfully identified high-risk HPV genotypes in OPSCC [22], [33], [34], [35], [36]. To date no large study has utilized LINEAR ARRAY HPV® Genotyping in OPSCC to detect and resolve all HPV16 and p16 discrepancies.
Section snippets
Study population
All patients with a first primary diagnosis of oropharyngeal squamous cell carcinoma between 1992 and 2007 at University of Maryland Greenebaum Cancer Center (UMGCC) were retrospectively reviewed (n = 467). The inclusion criteria were no prior history of oropharyngeal cancer and available pre-treatment biopsy material for analysis. 185 patients met the inclusion criteria. Data collected from review of patients medical records included: age, race, gender, tobacco and alcohol use, tumor, nodal,
Patient population
A total of 185 primary index cases had available tissue for HPV DNA testing, and p16 IHC was evaluable in 184 of 185 cases.
The clinicopathologic characteristics by HPV status are summarized in Table 1. A total of 67 of 185 patients were positive for HPV16 (36%), 73 of 185 were positive for any high risk HPV (HR HPV) (39%), and p16 IHC was positive in 75 of 184 patients (41%). 114 patients (62%) were Caucasian, 70 patients were African–American (38%), and 1 patient was Asian (<1%).
There was a
Discussion
In this study, we found p16 IHC had strong correlation with HR HPV infection, a concordance of 92%. Twenty-one out of 184 cases (11%) had discordant HPV16 and p16 results. In our population, a minority of HR HPV infections were due to a type other than HPV16 (6/73, 8%), but importantly in patients that were HPV16−/p16+, 40% (6/15) were found by LAHPV testing to be positive for another HR HPV type. P16 IHC positivity offered similar prognostic information as HR HPV testing, and patients that
Conflict of interest
The authors of this study have no financial or personal conflict of interest.
Acknowledgement
None.
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