Circulating Tumor HPV DNA in Patients with Head and Neck Carcinoma: Correlation with HPV Genotyping

Circulating tumor human papillomavirus DNA (ctHPVDNA) testing using digital-droplet polymerase chain reaction (PCR) detects fragments of tumor-modified human papillomavirus (HPV) in the plasma of patients with HPV-associated head and neck squamous cell carcinomas (HNSCCs). Its impact on tumor surveillance and primary diagnosis is limited by unresolved issues relating to sensitivity and specificity. The study population consisted of patients with HNSCC who had undergone ctHPVDNA testing. HPV status was determined by p16 immunohistochemistry and PCR-HPV genotyping on the tumor samples. For discrepant cases (HPV-positive/ctHPVDNA-negative), HPV status was confirmed by RNA in situ hybridization and, when possible, targeted single-nucleotide polymorphisms genotyping. A total of 167 patients had ctHPVDNA testing, and 141 tumors were HPV positive by p16 immunohistochemistry and PCR genotyping. Genotypes included types 16 (91.5%), 33 (4.3%), 35 (2.1%), and 18 (2.1%). ctHPVDNA was detected in 133 (94.3%) of HPV-positive HNSCCs but in none of the HPV-negative HNSCCs. Four of the 5 p16-positive cases that were negative by PCR and ctHPVDNA were positive by RNA in situ hybridization, and in 2 of these cases, rare high-risk genotypes were identified. ctHPVDNA had a sensitivity of 91.7%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 63.6%. The likelihood that patients with HPV-positive HNSCC have detectable ctHPVDNA is high. Non-HPV16 genotypes contribute to discrepancies but only in a small subset of cases. This finding validates ongoing efforts to use ctHPVDNA as a surveillance tool, and even as a primary diagnostic assay in patients presenting with masses in the neck and/or oropharynx.