Detection and significance of human papillomavirus, CDKN2A (p16) and CDKN1A (p21) expression in squamous cell carcinoma of the larynx

While a strong etiologic relationship between human papillomavirus and a majority of oropharyngeal squamous cell carcinomas has been established, the role of human papillomavirus in non-oropharyngeal head and neck carcinomas is much less clear. Here, we investigated the prevalence and clinicopathologic significance of human papillomavirus and its reported biomarkers, CDKN2A(p16) and CDKN1A(p21), in laryngeal squamous cell carcinomas in patients treated either with primary surgery and postoperative radiation or with definitive radiation-based therapy. Nearly all of 76 tumors were keratinizing and none displayed the nonkeratinizing morphology that is typically associated with human papillomavirus infection in the oropharynx. However, CDKN2A(p16) immunohistochemistry was positive in 21 cases (28%), and CDKN1A(p21) in 34 (45%). CDKN2A(p16) and CDKN1A(p21) status strongly correlated with each other (p = 0.0038). Yet, only four cases were human papillomavirus positive by DNA in situ hybridization or by reverse transcriptase polymerase chain reaction E6/E7 mRNA [all four were CDKN2A(p16) and CDKN1A(p21) positive]. Unexpectedly, 9 additional tumors out of 20 CDKN2A(p16) positive cases harbored high-risk human papillomavirus DNA by polymerase chain reaction. For further investigation of this unexpected result, in situ hybridization for E6/E7 mRNA was performed on these 9 cases and all were negative, confirming the absence of transcriptionally active virus. Patients with CDKN1A(p21) positive tumors did have better overall survival (69% at 3 years) than those with CDKN1A(p21) negative tumors (51% at 3 years) [p = 0.045]. There was also a strong trend towards better overall survival in the CDKN2A(p16) positive group (p=0.058). Thus, it appears that the role of human papillomavirus is more complex in the larynx than in the oropharynx and that CDKN2A(p16) and CDKN1A(p21) expression may not reflect human papillomavirus driven tumors in most cases. Because of this, CDKN2A(p16) should not be used as a definitive surrogate marker of human papillomavirus driven tumors in the larynx.