Human Papilloma virus is about 55 nm in diameter. It has a single circular double stranded DNA molecule and belongs to the family papillomaviridae. Its genome is made up of 7,200 – 8,000 base pairs with a molecular weight of 5.2 × 10⁶ D. On the basis of DNA base pair (bp) distribution, the viral DNA is divided into three parts: first a 4,000 bp region that responsible for viral DNA replication and cell transformation, second 3,000 bp region that encodes the structural proteins of the virus particles and last 1,000 bp non-coding region (NCR) that contains the origin of viral DNA replication.

Zur et al suggested that the genomic HPV DNA has nine open-reading frame sequences (ORFS) -present on single strand of DNA and are divided into seven early (E) and two late-phase genes (L). The transcription of viral DNA is regulated by early phase gene, while the capsid proteins (involved in viral spread) are regulated by late phase gene 23. The early-phase gene (E) encodes the E1, E2, E5, E6, and E7 proteins. E1 and E2 gene products regulated the transcription and replication of viral proteins and E5 gene product transcribed from the episomal region of the viral DNA 24. The E6 and E7 oncoprotiens are usually under control of E1 and E2 inhibitory genes. These genes have the ability to de-stimulate the tumor suppressor function and regulate the functions of the p21, p53, and pRb proteins, resulting in apoptosis, DNA repair and cell cycle control and may finally lead to cellular immortalization. (Fig. 1) The non-coding, long control region (LCR) contains binding sites for the E1 and E2 gene products, located just upstream of the promoter sequence 97 (P 97) which controls the transcription of the E6 and E7 oncogenes 25.

HPV must adhere to a specific receptor protein on the keratinocytes membrane. Once the virus entered into the cell, it transforms itself of its protein coat and the viral DNA may then utilize host cell themselves. These viruses elaborate early gene proteins (E) that are able to regulate the host cell cycle, or mitotic capabilities. The E6 and E7 proteins are most important in this respect; they bind two host proteins that are regulators of the keratinocytes at the time of cell division. E6 binds to a protein designated p53, a molecule that arrests cell division. However, once bound, it is degraded and this inhibition of keratinocytes mitosis is abrogated. Likewise, E7 binds a protein termed Rb; and, similarly, cell cycle regulation is troubled.

On the basis of their genotype, more than 120 types of HPV viral DNA genotypes have been fully sequenced 2627. It classified on the bases of their infection in epithelial cells and the ability to effect cellular transformation for e.g. HPV 1 is responsible for the infection in cutaneous cell while HPV 6, 11, 18 for mucosal epithelial cells of the oral cavity, oropharynx, anogenital tract and uterine cervix 28. The potentially oncogenic HPV is divided into high and low-risk types. The high-risk HPV such as 16, 18, 31, 33, 35, 52, 58, 59, 68, 73, and 82 are responsible for malignancies while the low-risk sub types (6, 11, 40, 42, 43, 44, 54, 61, 70, 72 and 81) are rarely found in carcinoma and frequently connected with benign and potentially malignant lesions of the head and neck.

Although HNSCC is closely linked to tobacco and alcohol use, there is an increasing incidence HPV16-related HNSCC arising in the oropharynx 29223031. Bouda et al suggested that high risk HPV E6/E7 transcripts and viral integration have also been detected in HNSCC. Transcriptionally active HR-HPVs, particularly HPV-16, are found in a subset of HNSCC. HPV16-associated carcinogenesis is mediated by expression of the viral E6 and E7 oncoproteins, which cause deregulation of the cell cycle by inactivating p53 and pRb respectively 26. HNSCC with transcriptionally active HPV16 DNA are characterized by occasional chromosomal loss, whereas HNSCCs lacking HPV DNA are characterized by gross deletions that involve whole or large parts of chromosomal arms and that already occur early in HNSCC development. These distinct patterns of genetic alterations suggest that HPV16 infection is an early event in HNSCC development 32. Chen et al suggested that the combined variants of p53 and p73 significantly increase the risk of HPV16-associated oral cancer, especially among never-smokers 33. In another report, they studied the p73 G4C14-to-A4T14 polymorphism may modulate the risk of HPV-16-associated oropharynx squamous cell carcinoma (SCCOP) and the p73 variant genotypes may be markers of genetic susceptibility to HPV-16-associated SCCOP, particularly in never smokers and never drinkers 34. Ji et al reported that p73 polymorphism was connected with HPV-16 in HNSCC and may serve as a marker of positive HPV-16 tumor in patients with HNSCC, in oropharyngeal cancer 35. Li et al suggested that this p73 polymorphism may be a risk marker for genetic susceptibility to HNSCC 36.

Pintos et al reported that HPV 16 was identified in tonsil-related cancers. 37. HPV has been found to be the most significant positive prognostic factor in patients with oropharyngeal tumors, with a 60–80% reduction in the risk of death 38. HPV positivity designates a specific subgroup of oropharyngeal squamous cell carcinomas that arise preferentially among individuals with no consumption of tobacco and alcohol and that have a favorable outcome attributable to an increased sensitivity toward radiotherapy 39.

Detection methods of HPV in benign lesions indicates that not all types of viral infections can cause disease and it would be essential to recognize the factors that determine its capability to induce malignant transformation in head and neck lesions. Respiratory papillomatosis associated with human papilloma virus (HPV) infection is the most common benign laryngeal neoplasm 55. Laryngeal papillomatosis is the most frequent benign neoplasia in children and it is caused by HPV 6 and 11. The lesions are exophytic and highly recurrent, compromising the airway mucosa, mainly the larynx 56. Juvenile laryngeal papillomatosis is a rare condition caused by HPV 57. DeVoti et al reported that recurrent respiratory papillomas (RRP) are benign airway tumors, caused primarily by HPV types 6 and 11 58. Castro et al reported the prevalence of HPV 6, 11 in normal oral mucous membrane. In oral benign lesions associated with HPV, a prevalence of HPV 6 and 11 was observed in squamous cell papilloma (SCP) and condyloma acuminatum, while HPV 2 and 57 were more prevalent in verruca vulgaris lesions 59. Fischer et al suggested that the applied broad-spectrum PCR system is a reliable tool in the detection of HPV DNA in benign lesions of the upper aerodigestive tract 60. Hoffmann et al suggested that HPV is correlated to a lesser extent to infectious mucosal lesions than to proliferative lesions. Furthermore, the results emphasize that the presence of HPV in specific lesions does not occur by chance, but represents a specific infection of the mucosa leading to proliferation and even to malignancy 61. (Table 1)

Several investigators have studied the prevalence of HPV in potentially malignant lesions, hoping to find a similar HPV prevalence as in malignant diseases. An increasing prevalence of HPV in premalignant lesions suggests that it may play a role in malignant transformation. Ha et al reported 1% prevalence of HPV 16 and 18 in premalignant oral lesions by using the quantitative PCR. 21. On the other hand, Bagan et al did not find any association between HPV DNA an PCR in proliferative verrucous leukoplakia (PVL) and HPV 62.

Furrer et al reported 41% HPV DNA detection by PCR-Southern blot analysis in premalignant and malignant lesions 63. Ostwald et al studied the occurrence of DNA of different subtypes of HPV 6/11, 16 and 18 detected by using highly sensitive molecular techniques like PCR/Southern blot hybridization and reported that 22.2% oral leukoplakias (OL) and 15.4% oral lichen planus (OLP) lesions were positive in HPV DNA 64. Campisi et al studied the prevalence of HPV infection in OL and OLP in comparison with healthy oral mucosa and reported that HPV DNA was found in 17.6% of OL and in 19.7% of OLP 65. Luo et al reported that prevalence of HPV was 30.4% in precancerous lesions through nested PCR and gene-chip arrays 66. (Table 2)

Recently, a study was conducted by the author's group with the aim to analyze the high-risk HPV DNA in oral submucous fibrosis (OSMF) and to determine the role of HPV infections. 105 cases, 33(31.4%) patients were positive for high risk HPV, while 72 (68.6%) were negative. On correlating HPV with histopathological grading, 7(29.1%) patients of grade I, 11(28.9%) of grade II and 15(34.8%) of grade III OSMF were positive. While correlating addiction habits with HPV, 18 (34.6%) areca nut chewers were positive and showed a significant p value (<0.05). The results showed that the level of agreement between the HPV and koilocytosis was moderate, with a Cohen kappa value of 0.524 (95% confidence interval [CI]. 0.3406 to 0.7081). The sensitivity of the hybrid capture test vis-à-vis presence of koilocytosis was 59% (95% CI: 0.4427 – 0.7363) and specificity was 91% (95% CI: 0.8102 – 0.9714) while the positive predictive value was 84% (95% CI: 0.6810 – 0.9489) and negative predictive value was 73% (95% CI: 0.6190 – 0.8330 (Unpublished data). Chen et al reported the positivity of HPV16 as 52.6% and HPV 18 as 25% in OSMF by the PCR method 67. Vidal et al reported 72.5% negative for low and high risk HPV DNA, 22.5% positive for low and high risk HPV DNA, 2.5% positive for low risk HPV DNA and 2.5% positive for high risk HPV DNA in 40 oral carcinoma cases by the Hybrid Capture technique 68.

Human papillomavirus especially the high-risk (HR) types (16 and 18), are widely recognized in the promotion of tumorigenesis in the uterine cervical squamous cell carcinoma 18. High-risk HPV are predominantly found in OSCC and may play a role in its progression, while low-risk sub types are usually associated with oral precancerous lesions. Koppikar et al studied the HPV DNA in oral carcinoma by PCR amplification and reported that HPV could contribute to carcinogenesis 69.

D'Costa et al suggested that HPV 16 plays a direct role in a certain populations of oral cancers whereas in a subpopulation, HPV16 infection may be vital in the early events associated with development of potentially oral lesion to malignancy 70. Mishra et al reported that involvement of p65 in HPV infected oral cancer may be linked to improved differentiation and better prognosis of the disease 71. König et al suggested that over expression of p16 has been demonstrated to be strongly related to the presence of HPV16, 18. HNSCC has been shown to be associated with HPV infection 72. Muenscher et al reported that the patients with no history of tobacco and/or alcohol consumption may also suffer from the laryngeal malignancy. There may be several factors such as individual predisposition, radiation, gastroesophageal reflux, viral infection, dietary factors and environmental influences 73. The presence of HPV infection in 35.5% of their cases suggests a possible role in the etiology of laryngeal squamous cell carcinoma (LSCC) and supports the role of high-risk types of HPV (16, 18 and 33) in its etiology. HPV infection is not likely to influence survival rates as an independent prognostic factor in patients with laryngeal cancer 74. Von et al suggested that the broad-spectrum PCR is a reliable method for detection of HPV-DNA 75.

Torrente et al reported that HPV DNA was found in 32% of laryngeal carcinoma biopsies. The genotypes identified were high-risk types, the most frequent being HPV 16. Viral DNA was integrated into the host genome (genotype HPV 16), providing supporting evidence for a role of HPV in the carcinogenic pathway of laryngeal squamous cell carcinoma 76. Montaldo et al reported that only two HPV genotypes (HPV 16 and HPV 31) were detected in oral carcinoma. 77. Agrawal et al recently reported that HPV16-positive HNSCC cases were more likely than HPV16-negative cases to have an oral HPV infection detected before and after therapy, consistent with a behavioral and/or biological disposition to infection 78. Various studies report the differences in the samples and molecular assays utilized in malignant lesions. (Table 3) 87888990919293949596979899100101102103104105106107.

Currently, two prophylactic HPV vaccines, one is quadrivalent 'Gardasil^®' developed by Merck which protects against HPV types 6, 11, 16 and 18 and another is bivalent Cervarix^® vaccine by Glaxo Smith Kline (GSK), protects against HPV types 16 and 18. Prophylactic vaccinations against high-risk HPV types eventually prevent a significant number of carcinomas. Both vaccines are Virus like particle (VLP) vaccines has been developed for primary HPV vaccination and targets HPV 16 and 18, while Gardasil, includes a standard alum adjuvant, also targets HPV 6 and HPV 11. These vaccines are recommended for vaccinating young adolescent girls at or before onset of puberty. Gardasil^® (Merck & Co, Bluebell, PA, USA) has gained regulatory approval from U.S.-Food and Drug Administration while Cervarix^® (GlaxoSmithKline, Rixensart, Belgium) has been approved in Australia and pending approval from regulatory agencies in the USA. (Table 4)

Giorgi Rossi et al reported that the identification of the HPV as the necessary cause of cervical cancer introduced two new tools for prevention: HPV DNA test and vaccine and suggested that vaccine and screening interventions must be integrated in a unique public health program and screening should use less aggressive protocols, to be less expensive and more sustainable and efficient 79. Marra et al suggested that a female-only vaccination programme is more cost effective compared with the current cytology-based pap smear screening programme, while the cost effectiveness of a male and female vaccination programme is generally less compared with female-only vaccination 80. The Swedish National Board of Health and Welfare (NBHW) decided that a vaccine that protects against cervical cancer caused by HPV should be included in the childhood vaccination directive as nationwide-programme targeting 12-yearold girls from 2010 as a part of the school-health programme. Currently, vaccination of girls 13–18 years of age is covered by the public insurance 81. Adams et al suggested that prophylactic HPV vaccination against HPV 16 and 18 has been shown to be highly effective in preventing HPV related malignancy in clinical trials. Newly introduced HPV vaccination program in the UK and elsewhere are ultimately likely to result in a further significant reduction in the incidence and mortality of cervical cancer. These vaccination programs will be most effective in early adolescence when prevalence of HPV infection is low. Consequently, vaccination program in the UK have been initially targeted at 12 to 13-year olds.

In 2007, New South Wales, Australia implemented the National human papillomavirus vaccination program, which provides quadrivalent HPV vaccine free to all women aged 12–26 years. In Australia, favorable estimates of cost effectiveness have supported funding of a 'catch-up' programme to females up to 26 years of age. 82. Brotherton et al reported that the estimated rate of anaphylaxis for quadrivalent HPV vaccine was significantly higher (IR = 2.6/100 000 doses; 95% CI 1.0–5.3) than identified in comparable school-based delivery of other vaccines like conjugated meningococcal C vaccine (IR = 0.1/100 000 doses; 95% CI 0.003–0.7) However, overall rates were very low and managed appropriately with no serious sequelae 83. Lawrence et al reported that two deaths were temporally associated with immunization; however, there was no evidence to suggest a causal association. They concluded that despite the low rate of adverse events following immunization in Australia, the passive surveillance system was sufficiently strong to detect safety signals associated with vaccination. Further studies are required before a clean chit can be given to its safety 84.

The Rural Southern areas of North Carolina, USA have accepted the HPV vaccine 85. Goncalves et al reported that the usefulness of the current HPV vaccine may be considered not only for the cervix but also for prevention of HPV 18 anal infection among immunosuppressed individuals 86. However in case of oral and oropharyngeal carcinoma, a careful search did not reveal any literature in relation to HPV vaccine.