Basics of tumor development and importance of human papilloma virus (HPV) for head and neck cancer.

Head and Neck Squamous Cell Carcinomas (HNSCC) are the 6(th) most common cancers worldwide. While incidence rates for cancer of the hypopharynx and larynx are decreasing, a significant increase in cancer of the oropharynx (OSCC) is observed. Classical risk factors for HNSCC are smoking and alcohol. It has been shown for 25 to 60% of OSCC to be associated with an infection by oncogenic human papilloma viruses (HPV). The development of "common" cancer of the head and neck is substantially enhanced by an accumulation of genetic changes, which lead to an inactivation of tumor suppressor genes or activation of proto-oncogenes. A more or less uniform sequence of different DNA-damages leads to genetic instability. In this context, an early and frequent event is deletion on the short arm of chromosome 9, which results in inactivation of the p16-gene. In contrast, for HPV-induced carcinogenesis, expression of the viral proteins E6 and E7 is most important, since they lead to inactivation of the cellular tumor-suppressor-proteins p53 and Rb. The natural route of transoral infection is a matter of debate; peroral HPV-infections might be frequent and disappear uneventfully in most cases. Smoking seems to increase the probability for developing an HPV-associated OSCC. The association of HNSCC with HPV can be proven with established methods in clinical diagnostics. In addition to classical prognostic factors, diagnosis of HPV-association may become important for selection of future therapies. Prognostic relevance of HPV probably surmounts many known risk-factors, for example regional metastasis. Until now, no other molecular markers are established in clinical routine. Future therapy concepts may vary for the two subgroups of patients, particularly patients with HPV-associated OSCC may take advantage of less aggressive treatments. Finally, an outlook will be given on possible targeted therapies.