Human papillomavirus in head and neck cancer: its role in pathogenesis and clinical implications.

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer with an annual incidence of approximately 400,000 worldwide. Although the principal risk factors for head and neck cancer remain tobacco and alcohol use, human papillomavirus (HPV) has recently been found to be etiologically associated with 20 to 25% of HNSCC, mostly in the oropharynx. HPV causes human cancers by expressing two viral oncoproteins, E6 and E7. These oncoproteins degrade and destabilize two major tumor suppressor proteins, p53 and pRb, through ubiquitination. Additional studies have shown that E6 and E7 can directly bind to multiple host proteins other than p53 and pRb (e.g., Bak and p21(Cip1)), further contributing to genetic instability. However, expression of E6 and E7 alone is not sufficient for cellular transformation, and the additional genetic alterations necessary for malignant progression in the setting of virus-induced genomic instability are unknown. In addition to the etiological differences, HPV-positive cancers are clinically distinct when compared with HPV-negative cancers with regard to treatment response and survival outcome, with tumor HPV-positivity being a favorable prognostic biomarker. Further understanding of carcinogenesis and clinical behavior of HPV-positive cancers will improve disease prevention, patient care, and surveillance strategies for HNSCC patients.