The etiologic implication and prognostic roles of p16-positive tumor status are well established for squamous cell cancers (SCCs) of the oropharynx (1) but remain controversial for nonoropharyngeal SCCs (non-OPCs) of the head and neck. In the oropharynx, human papillomavirus (HPV)–driven carcinogenesis leads to p16 overexpression, which renders p16 a logical surrogate for HPV tumor detection (2–4). However, non-OPCs do not have an analogous molecular profile. The overall prevalence of HPV- or p16-positive non-OPCs appears to be low (5–7). Furthermore, the proportion of p16-positive non-OPCs exceeds that for HPV-positive individuals (8–11), with only the former showing a survival benefit in limited studies (12). Therefore, consensus guidelines do not support testing of non-OPCs for HPV or p16 as their prognostic implications have not yet been established (13). In this issue of the Journal, Bryant et al. challenge this dogma by suggesting that p16 may still have prognostic value (14). Recent large studies with centralized pathologic evaluation and geographic and anatomic site heterogeneity have examined the role of p16 in non-OPCs (5,6,8–12,15–17), notwithstanding the inherent biases of retrospective studies, lack of generalizability due to eligibility criteria for a clinical trial or care at an academic institution, and limited pathologic evaluation and survival data. Bryant et al. (14) examine this question with a novel strategy to overcome inherent limitations or biases of prior studies that may have misled us to the belief that p16 is not relevant in non-OPCs. A robust data set of American veterans with a large sample size and low health care migration (effectively serves as prospective data) was queried to evaluate overall, cause-specific (CSS), and competing survival. In this study (14), p16 status was not centrally reviewed; however, given that there is high interrater agreement regarding p16 interpretation (18), the retrospective data abstraction is likely sufficient. It is unlikely that a consistent cutoff was used to determine p16 positivity at 120 different centers. Only 29% of tumors considered positive were indeed “strong and diffuse” (equivalent to oropharynx criteria), with the majority graded as “positive NOS.” Second, p16 was available for only 8% (n = 387) of the 4594 non-OPCs, which raises concern for selection bias. Indeed, Supplementary Table 3 supports that p16 testing was more commonly performed for patients who were white, had a lower comorbidity index, had lower current tobacco use, were employed, and had laryngeal primary tumors if nonoropharyngeal (P < .001 for each) as compared with patients not tested. In their multivariable regression model (shown in Table 3), patients with younger age at diagnosis and higher income, independent predictors of improved survival, had the highest odds of p16 testing. Another important risk factor, which was clinically but not analytically available, that may have impacted the decision for p16 testing is lifetime tobacco exposure. Therefore, general prognostic factors observed by clinicians at the time of clinical evaluation may have led to differential p16 testing. Indeed, CSS was higher for non-OPCs tested for p16 as compared with those that were not (Figure 2B). In the Bryant analysis (14), 20% of non-OPCs overall and at each anatomic site considered (oral cavity, larynx, and hypopharynx) were p16-positive. Although this estimate falls within the range of some prior data, only 5.9% (n = 23) (Table 1) of p16-positive tumors had strong or diffuse staining. The latter estimate is more consistent with recent large multi-institutional retrospective studies that had centralized pathologic review with strict p16 criteria (70% cutoff or H score). A four-institution consortium systematically evaluated a larger sample size of non-OPCs and found that 11% and 4.5% of oral cavity (n = 409) and larynx (n = 404) SCCs, respectively, were p16-positive (9,10). Another two-institution study (n = 623) found that 10% were p16-positive (site-specific prevalence 5%–13%) (11). Therefore, it may be that when a strict cutoff is used, even in this data set, the prevalence of p16 may be lower than 20%. From other series, it is worthwhile to note that there is heterogeneity for p16 across sites and geographically (5,6,17). An additional consideration is that anatomic site classification not rigorously defined by comprehensive operative examination or imaging review can suffer from misclassification and lead to overestimates of p16 in nonoropharyngeal sites, when indeed the anatomic site of origin is the adjacent oropharynx, replete with p16-positive tumors. Next, p16 positivity was associated with a consistent significant reduction in risk of overall survival (OS) and CSS (hazard ratios [HRs] = 0.35–0.42), but not competing mortality (HRs = 0.46–0.56, Prange = .04–.11) for non-OPCs overall. In contrast to a similarly sized analysis with centralized p16 detection and interpretation, known tobacco exposure, there was no interaction between p16 status and anatomic site (12). Considering that lifetime tobacco exposure was not accounted for in the multivariable models, it is possible that there was residual confounding due to this recognized independent prognostic factor (19). However, the consistency of the hazard ratios, including those in the anatomic site–specific models (albeit not statistically significant), indicates that despite the potential limitations, p16 tumor status may have prognostic significance. The question to consider is what future steps are necessary to advance the authors’ proposal to recognize p16 as a prognostic biomarker of clinical utility in non-OPCs? First, this analysis would need to be reproduced in a separate validation cohort with standardized therapy, rigorous anatomic site classification, uniform assessments of p16, and clinical disease status. The Department of Veterans Affairs population may not be generalizable to the broader population because of specific exposures including occupational, socioeconomic status, tobacco and alcohol use, and comorbidity profile. Second, it will be critical to understand the performance properties of p16 assays in nonoropharynx (sensitivity, specificity, and predictive value) if the cutoff used in oropharynx cancer is applicable. Third, given the apparently low proportion of p16-positive non-OPCs, it is not expected that uniform testing of all tumors will be warranted (or cost-effective). Determining strategies to identify an enriched subset could render p16 testing more clinically effective and cost-effective. Last, prospective studies should test whether the prognostic benefit of rigorously and consistently defined p16 tumor status has therapeutic implications. If p16 is confirmed as a prognostic biomarker in non-OPCs, further risk stratification and understanding of the effect or interaction of other risk factors or exposures (eg, smoking, education) with p16 on survival estimates will be necessary. Although not essential to clinical application of a biomarker, understanding the etiologic implication of p16 may be of interest. A very small proportion of non-OPCs were HPV-positive, although few had both p16 and HPV in situ hybridization (n = 32) results. Indeed, patchy or intermediate p16 expression does not appear to indicate the presence of HPV (Supplementary Table 4, available online) (20–22). Therefore, p16 for a negligible portion of non-OPCs are HPV-related, and the others are p16-positive for other potential reasons including misclassification. Therefore, the present data are insufficient to designate p16 as a prognostic biomarker for non-OPCs. The observations in this study require further rigorous evaluation to determine whether they are attributable to p16 or alternative clinical factors. Notes Affiliations of authors: Department of Otolaryngology – Head and Neck Surgery and Bloomberg-Kimmel Institute for Cancer Immunotherapy, Johns Hopkins University, Baltimore, MD (CF); Department of Immunology and Department of Otolaryngology, University of Pittsburgh, PA (RLF); Cancer Immunology Program, UPMC Hillman Cancer Center, Pittsburgh, PA (RLF). The authors have no conflicts of interest to disclose. References 1 D'Souza G, Kreimer AR, Viscidi Ret al. , Case-control study of human papillomavirus and oropharyngeal cancer. N Engl J Med . 2007; 356 19: 1944– 1956. Google Scholar CrossRef Search ADS PubMed 2 Khleif SN, DeGregori J, Yee CLet al. , Inhibition of cyclin D-CDK4/CDK6 activity is associated with an E2F-mediated induction of cyclin kinase inhibitor activity. Proc Natl Acad Sci U S A. 1996; 93 9: 4350– 4354. Google Scholar CrossRef Search ADS PubMed 3 Chung CH, Gillison ML. Human papillomavirus in head and neck cancer: Its role in pathogenesis and clinical implications. 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JNCI: Journal of the National Cancer Institute – Oxford University Press
Published: Jun 5, 2018
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