early (e) oncoproteins e5, e6 and e7 and the late (l) capsid proteins l1 and l2. the virus gains access to the mucosa through microlesions, where it infects the basal layer of cells, which are still able to proliferate. while the virus does not replicate in these cells, expression of its early genes stimulates proliferation and lateral expansion of the basal cells. as this moves the virus particles into the overlying suprabasal layers, late viral gene expression occurs, enabling replication of the circular viral genome (see figure) and structural proteins. as these are pushed into the most superficial mucosal layers, complete viral particles are assembled and released. oncogenesis an increased risk of hpv+opc is observed more than 15 years after hpv exposure, pointing to a slow development of the disease, similar to that seen in cervical cancer. relative to hpv-opc, the oncogenic molecular progression of hpv+opc is poorly understood. the two main viral oncoproteins of the high risk hpv types are e6 and e7. these are consistently expressed in malignant cell lines, and if their expression is inhibited the malignant phenotype of the cancer cells is blocked. either of these oncoproteins can immortalise cell lines, but are more efficient when both are expressed, since their separate molecular roles are synergistic. the e6 and e7 oncogenes become integrated into host-cell dna, and the oncoproteins they express interfere with a variety of predominantly antiproliferative cellular regulatory mechanisms. they bind to and inactivate the best known of these mechanisms, the tumor suppressor proteins p53 and retinoblastoma protein prb (prb) leading to genomic instability and then cell cycle deregulation (see chung et al., 2016 fig. 35.2). further, yet to be elicited, mechanisms are required for the final steps of malignant transformation of hpv infected cells. hpv- and hpv+opc are distinguishable at the molecular level. the naturally occurring (wild type) p53 is widely involved in cellular processes, including autophagy, response to dna damage, cell cycle regulation and senescence, apoptosis and the generation of adenosine triphosphate (atp) through oxidative phosphorylation. the gene encoding p53 is inactivated by e6 at the protein level and is found as the wild type in hpv+opc but mutated in hpv-opc. in hpv+opc p53 protein undergoes accelerated degradation by e6, drastically reducing its levels, while in hpv-opc it undergoes genetic mutation, which may result in synthesis of an abnormal p53 protein, that may not only be inactive as a tumour suppressor, but can also bind and inactivate any non-mutated wild type p53, with an increase in oncogenic activity. although p53 mutations occur in hpv+opc, they are far less common than in hpv-opc (26% vs 48%), and do not appear to affect clinical outcome. the prb protein is inactivated by e7 in hpv+opc, but in hpv-opc it is the p16 tumour suppressor part of the prb tumour suppressor network that is inactivated. also the prb pathway is inactivated by e7 instead of cyclin d1 amplification. cdkn2a is a tumour suppressor gene that encodes a tumor suppressor protein, p16 (cyclin-dependent kinase inhibitor 2a) and inhibits the kinase activity of the cyclin-dependent kinases cdk4 and cdk6, which in turn induce cell cycle arrest. p16 expression is cell cycle dependent and is expressed focally in only about 5–10% of normal squamous epithelium. like most hpv+ cancers, hpv+opc express p16 but the latter does not function as a tumour-suppressor, because the mechanism by which this is achieved, prb, has been inactivated by e7. p16 is upregulated (over-expressed) due to e7-related loss of prb with reduced negative feedback, whereas it is downregulated in up to 90% of hpv-opc. this diffuse over-expression in the tumour cells provides a diagnostic marker for hpv involvement. although hpv e6 and e7 reduce tumour suppressor activity, they do so less than genetic and epigenetic processes do in hpv-opc. the tonsillar epithelia (palatine and lingual) share similar nonkeratinization characteristics with the cervix, where hpv infection plays the major role in cases of cervical cancer. also e6 and e7 may make hpv+opc more immunogenic than hpv-opc, since anti-e6 and e7 antibodies may be detected in these patients. this in turn could restrict the malignant behaviour of hpv+opc and the presence of antibodies has been associated with a better prognosis, while treatment may enhance the immunogenicity of the tumour, and hence improve response, although to what extent is not clear. outcomes are also associated with improved adaptive immunity. diagnosis rhinoscope used in diagnosis and surveillance ct scan in transverse plane, viewed from below, showing a contrast enhancing right tonsil mass due to hpv+opc biopsy initial diagnosis requires visualisation of the tumour either through the mouth or endoscopically through the nose using a rhinoscope, illustrated to the right, followed by biopsy. differentiating hpv+opc from hpv-opc hpv+opc is usually diagnosed at a more advanced stage than hpv-opc, with 75–90% having involvement of regional lymph nodes. furthermore, hpv+opc is more likely to be poorly differentiated with nonkeratinized or basaloid cells. genetic signatures of hpv+ and hpv- opc are different. hpv+opc is associated with expression level of the e6/e7 mrnas and of p16. hpv16 e6/e7-positive cases are histopathologically characterized by their verrucous or papillary (nipple like) structure and koilocytosis of the adjacent mucosa. approximately 15% of hnsccs are caused by hpv16 infection and the subsequent constitutive expression of e6 and e7, and some hpv-initiated tumors may lose their original characteristics during tumor progression. high-risk hpv types may be associated with oral carcinoma, by cell-cycle control dysregulation, contributing to oral carcinogenesis and the overexpression of mdm2, p27 and cathepsin b. hpv+opc is not merely characterized by the presence of hpv-16: only the expression of viral oncogenes within the tumor cells plus the serum presence of e6 or e7 antibodies is unambiguously conclusive for hpv+opc. there is not a standard hpv testing method in head and neck cancers, both in situ hybridization (ish) and polymerase chain reaction (pcr) are commonly used. both methods have comparable performance for hpv detection, however it is important to use appropriate sensitivity controls. immunohistochemistry (ihc) staining of the tissue for p16 is frequently used as a cost-effective surrogate for hpv in opc, compared to ish or pcr but there is a small incidence of hpv-negative p16-positive disease accounting for about 5% of hpv-opc. staging staging is generally by the uicc/ajcc tnm (tumour, nodes, metastases) system. staging is based on clinical examination, diagnostic imaging, and pathology. on imaging, involved lymph nodes may appear cystic, a characteristic of hpv+opc. hpv+opc has been treated similarly to stage-matched and site-matched hpv unrelated opc, but its unique features, which contrast smoking-related hpv-opc head and neck cancers, for which patients' demographics, comorbidities, risk factors, and carcinogenesis differ markedly, suggest that a distinct staging system be developed to more appropriately represent the severity of the disease and its prognosis. standard ajcc tnm staging, such as the seventh edition (2009) while predictive for hpv-opc has no prognostic value in hpv+opc. the 8th edition of the ajcc tnm staging manual (2016) incorporates this specific staging for hpv+opc. as of 2018, treatment guidelines are evolving to account for the different outcomes observed in hpv+opc. consequently, less intensive (de-intensification) use of radiotherapy or chemotherapy, as well as specific therapy, is under investigation, enrolling hpv+opc in clinical trials to preserve disease control and minimise morbidity in selected groups based on modified tnm staging and smoking status. hpv+ cancer of the oropharynx are staged as (ajcc 8th ed. 2016): tumour stage t0 no primary identified t1 2 cm or less in greatest dimension t2 2–4 cm t3 >4 cm, or extension to lingual surface of epiglottis t4 moderately advanced local disease, invading larynx, extrinsic muscle of tongue, medial pterygoid, hard palate, or mandible or beyond nodal stage nx regional lymph nodes cannot be assessed n0 no regional lymph nodes involved n1 one or more ipsilateral nodes involved, less than 6 cm n2 contralateral or bilateral lymph nodes, less than 6 cm n3 lymph node(s) larger than 6 cm clinical stage stage i: t0n1, t1–2n0–1 stage ii: t0n2, t1–3n2, t3n0–2 stage iii: t0–3n3, t4n0-3 stage iv: any metastases (m1) however, the published literature and ongoing clinical trials use the older seventh edition that does not distinguish between hpv+opc and hpv-opc - see oropharyngeal cancer - stages. the t stages are essentially similar between ajcc 7 and ajcc 8. with two exceptions. tis (carcinoma in situ) has been eliminated and the division of t4 into substages (e.g. t4a) has been removed. the major changes are in the n stages, and hence the overall clinical stage. n0 remains the same, but as with the t stage, substages such as n2a have been eliminated. extracapsular extension (ece), also referred to as extranodal extension (ene), which is invasion by the tumour beyond the capsule of the lymph node has been eliminated as a staging criterion. this results in a hpv+opc tumour being given a lower stage than if it were hpv-opc. for instance, a 5 cm tumour with one ipsilateral node involved that is 5 cm in size but has ece would be considered t3n3bm0 stage ivb if hpv- but t3n1m0 stage ii if hpv+. prevention vial of hpv vaccine avoiding exposure prevention of hpv+opc involves avoiding or reducing exposure to risk factors where possible. vaccination about 90% of hpv+opc carry hpv 16, and another 5% type 18. these two types are both targets of available vaccines. hpv vaccines given prior to exposure can prevent persistent genital infection and the consequent precancerous state. therefore, they have a theoretical potential to prevent oral hpv infection. a 2010 review study has found that hpv16 oral infection was rare (1.3%) among the 3,977 healthy subjects analyzed. treatment the goals of treatment are to optimise survival and locoregional disease control, and prevent spread to distant areas of the body (metastasis), while minimising short- and long-term morbidity. there is no high quality level i evidence from prospective clinical trials in hpv+opc, therefore treatment guidelines must rely on data from treatment of opc in general and from some retrospective unplanned subsetting of those studies, together with data for head and neck cancer in general. treatment for opc has traditionally relied on radiotherapy, chemotherapy and/or other systemic treatments, and surgical resection. depending on stage and other factors treatment may include a combination of modalities. the mainstay has been radiotherapy in most cases. a pooled analysis of published studies suggested comparable disease control between radiation and surgery, but higher complication rates for surgery +/- radiation. ideally a single modality approach is preferred, since triple modality is associated with much more toxicity, and a multidisciplinary team in a large centre with high patient volumes is recommended. differences in response to treatment between hpv-opc and hpv+opc may include differences in the extent and manner in which cellular growth-regulatory pathways are altered in the two forms of opc. for instance in hpv+opc the hpv e6 and e7 oncogenes merely render the p53 and prb pathways dormant, leaving open the possibility of reactivation of these pathways by down-regulating (reducing) expression of the oncogenes. this is in contrast to the mutant form of p53 found in hpv-opc that is associated with treatment resistance. furthermore, it is suggested that the effects of e6 and e7 on these pathways renders the tumour more radiosensitive, possibly by interference with mechanisms such as dna repair, repopulation signalling, and cell-cycle redistribution. the microenvironment is also important, with radiation increasing host immune response to viral antigens expressed on the tumour. also, there is an association between an increase in tumour-infiltrating lymphocytes and in circulating white blood cells in hpv+opc patients and better prognosis. this implies a role for an adaptive immune system in suppressing tumour progression. surgery historically, surgery provided the single approach to head and neck cancer. surgical management of opc carried significant morbidity with a transcervical (through the neck) approach, often involving mandibulotomy, in which the jawbone (mandible) is split. this is referred to as an open surgical technique. consequently, surgical approaches declined in favour of radiation. in the united states, the use of surgery declined from 41% of cases in 1998 to 30% by 2009, the year that the food and drug administration approved the use of the newer techniques. these improvements in surgical techniques have allowed many tumours to be resected (removed) by transoral (through the mouth) surgical approaches (tos), using transoral endoscopic head and neck surgery (hns). consequently, surgery became used more, increasing to 35% of cases