Abstract
Head and neck cancers are unique in so far that 2 major oncogenic viruses, EBV and HPV infect adjacent anatomy and cause nasopharyngeal and oropharyngeal cancers respectively. Dominant recognised carcinogens are alcohol and tobacco but some head and neck cancers have been found to have mixed carcinogens (including betel leaf, areca nuts, slaked lime, viruses, etc) involved in their oncogenesis and conversely, groups of patients with unknown or less dominant carcinogens involved in their development. These cancers may have had viral involvement in the past but then lost most of their viral nucleic acids (be they DNA and/or RNA) below a detection threshold, thus rendering them virus-negative. Some of these virus-negative tumours appear to have mutagenic signatures associated with virus-positive cancers i.e. from the APOBEC defence mechanism which is known to mutate viral nucleic acids as well as cause collateral damage to host DNA, with subsequent development of strongly viral prejudiced mutational signatures. These mechanisms are likely to be less efficient at oncogenesis than traditional direct EBV and HPV oncogenes driving mutagenesis, thus accounting for the smaller frequencies of these cancers found. More profound investigations of these unusual tumours are warranted to dissect out these mechanistic pathways.
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