Email updates

Keep up to date with the latest news and content from Head & Neck Oncology and BioMed Central.

Open Access Highly Accessed Commentary

Controversies surrounding human papilloma virus infection, head & neck vs oral cancer, implications for prophylaxis and treatment

Giuseppina Campisi1* and Lucia Giovannelli2

Author Affiliations

1 Settore di Medicina Orale, Dip. di Scienze Stomatologiche, Università Palermo, Via del Vespro 129-90127, Palermo, Italy

2 Servizio di Virologia, Dip. di Scienze per la Promozione della Salute, Università Palermo, Via del Vespro 129-90127, Palermo, Italy

For all author emails, please log on.

Head & Neck Oncology 2009, 1:8  doi:10.1186/1758-3284-1-8

The electronic version of this article is the complete one and can be found online at: http://www.headandneckoncology.org/content/1/1/8


Received:20 January 2009
Accepted:30 March 2009
Published:30 March 2009

© 2009 Campisi and Giovannelli; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Head & Neck Cancer (HNC) represents the sixth most common malignancy worldwide and it is historically linked to well-known behavioural risk factors, i.e., tobacco smoking and/or the alcohol consumption. Recently, substantial evidence has been mounting that Human Papillomavirus (HPV) infection is playing an increasing important role in oral cancer. Because of the attention and clamor surrounding oral HPV infection and related cancers, as well as the use of HPV prophylactic vaccines, in this invited perspective the authors raise some questions and review some controversial issues on HPV infection and its role in HNC, with a particular focus on oral squamous cell carcinoma.

The problematic definition and classification of HNC will be discussed, together with the characteristics of oral infection with oncogenic HPV types, the frequency of HPV DNA detection in HNC, the location of HPV-related tumours, the severity and prognosis of HPV-positive HNC, the diagnosis of oral HPV infection, common routes of oral infection and the likelihood of oro-genital HPV transmission, the prevention of HPV infection and novel therapeutic approaches.

Background

Taking into consideration the attention and clamor surrounding Human Papilloma Virus (HPV) infection and related cancers, HPV vaccine controversies, as well as the recent Nobel Prize awarded to Prof. zur Hausen for his research on HPV and cervical cancer, authors believe it opportune, in this invited perspective, to raise various questions and review some of the most controversial issues related to HPV and its role in Head & Neck Cancer (HNC) and particularly in oral squamous cell carcinoma (OSCC), as well as the diagnosis of oral HPV infection and its oro-genital transmission.

HNC represents the sixth most common malignancy worldwide [1], and it is historically linked to several behavioural risk factors (i.e., tobacco smoking and/or the consumption of alcohol). However, this term defines a heterogeneous group of malignant tumours, involving several different several sub-sites. The majority of HN malignancies are squamous cell carcinomas (SCC) and they originate from the epithelium which lines the upper aero digestive tract, i.e., the oral cavity, the pharynx and the larynx. Arising in a multistep process resulting from the gathering of genetic and epigenetic defects and clonal spreading out of given cell populations [2], HN malignancies are known as HNSCC.

HPVs are epitheliotropic oncogenic DNA viruses with more than 120 identified genotypes: the so-called high-risk (HR) HPV, like HPV 16 and 18, have been definitively recognised as being strongly associated with ano-genital (cervical) cancers. In patients with high-grade neoplasia and cancer, HR HPV DNA can usually be found integrated into host DNA. The oncogenic potential of HR HPV is attributable to its ability to insert specific DNA fragments (early genes E6 and E7) into the host cellular genome. As a result of this integration, various key functions of tumour suppressor factors (the p53 and pRb pathways) are abrogated, leading to defects in apoptosis, DNA repair mechanisms, cell cycle regulation and, finally, to cellular immortalization, thus inducing and maintaining the malignant phenotype.

The HPV involvement in HN carcinogenesis was first proposed in 1983 by Syrjanen et al. [3] and then supported by several other authors on the basis of the following evidence: 1) the well-assessed broad epitheliotropism of HPV; 2) the morphological similarities between oropharyngeal and genital epithelia [4]; 3) the ability of immortalizing human oral keratinocytes in vitro [5]; and 4) the strongly established etiological role of HR HPV in cervical SCC [6,7].

Whilst occurring in a lower percentage than in cervical mucosa, HR HPV E6/E7 transcripts and/or viral integration have also been detected in HNC [8] and, it has, therefore, been suggested that HR HPV (mostly HPV 16, 18, 33) are involved in the viral-dependent inactivation of p53 and Rb. This occurrence also justifies the increased incidence of HNC and the onset of the tumour in younger people [9], whether the most common risk factors are present or not. As well as being associated with genital and oral mucosa diseases, HPV infection has also been reported in cases of nasal inverting papilloma, which is usually a benign tumour but is associated with squamous cell carcinoma (SCC) in about 10% of cases. Previous analyses have identified HPV-16 DNA in 32% of inverted papillomas and 58% papillomas associated with carcinomas [10]. More recently, an active role in the malignant lesion has been suggested for HPV on the basis of the presence of the HPV oncogene E6 and E7 transcripts, indicating the integration of the viral genome [11]. However, further analysis is required to confirm that HPV is not only a bystander agent.

In addition to these logical statements, it is timely to raise the following questions and shed light on these controversies:

What is the frequency of HR HPV in HNC?

A very wide range of viral prevalence (0%–100%), in addition to the presence of HR HPV in oral normal mucosa [12,13], has been reported in the literature, even if with limited information regarding the natural history of oral HPV infection. Specifically relating to HPV 16 and 18, Kreimer et al [14] identified these genotypes in 16.0% and 3.9% respectively of 2,642 HNC reviewed in a recent systematic review of the literature; they calculated an overall prevalence of HPV in 25% of HNC vs 35.6% in oro-pharyngeal cancer and 23.5% in OSCC. Excluding any ethno-geographical bias among the patient groups examined, this wide range depends mainly on two variables: i) the site of the mucosa examined; and ii) technical issues (or the HPV molecular assay employed).

What is the precise location of the HPV-related tumour?

A great deal of confusion is created by the use of the generic term HNC, HNSCC or oral cancer in place of the specific OSCC, oro-pharyngeal or laryngeal carcinoma. This issue plays a critical role since specific epithelial areas of the upper aero-digestive tract (such as the squamous-columnar junction at the level of the tonsillar crypts and the glottides) display greatest susceptibility to HPV due to the easy exposure of the basal cells, and this is also the case with the meta-plastic epithelial area in the cervix. Hence, it is critical to group HNSCC together as a single entity with the consequent difficulty of comparing the data. Recent epidemiological and molecular data have indicated the involvement of HR HPV in a given subset of HNSCC [14-19] (i.e. oro-pharyngeal and Waldeyer's tonsillar ring SCC) have been found to be significantly related to HR HPV(especially HPV 16/18). HPV 16 was very recently identified in tonsil-related cancers (palatine tonsil and at the base of the tongue) in oral exfoliated cells together with serum antibodies against HPV 16 [20], in non-smokers and non-drinkers, and oro-pharyngeal SCC patients [21]. Comparing these data, no clear results for OSCC and HR HPV have so far emerged. Various studies report a significant association between HPV 16 and to a lesser extent HPV 18 with OSCC [13,22-25] with respect to the frequency of HPV in normal oral mucosa. In a recent meta-analysis [26] of studies (1988 – 2007) on HPV in HNSCC vs OSCC biopsies, we found that the pooled prevalence of HPV DNA in the overall samples was 34.5%, while it was 38.1% in OSCC and 24.1% in the non site-specific HNSCC group. Unfortunately, it was confirmed that only a few studies had observed a correct distinction between cancers at oral and oro-pharyngeal sites, as recommended by the American Joint Committee on Cancer. Finally, the misclassification of some HPV-positive oro-pharyngeal cancers, such as OSCC, could partly explain the HPV-positivity of some "oral" cancers, thus even diminishing the real impact of HR HPV on oro-pharyngeal tumour onset [14,17].

What type of infection is a prerequisite for carcinogenesis?

As gleaned from the field of gynaecology, a persistent viral status represents a necessary although not sufficient basis for HPV-related lesions [7,27-31]: persistent infection with a specific HR-HPV type must be maintained for at least 2 years and usually copies of the virus are found in great numbers in cervical mucosa. However, the virus is rarely found in oral mucosa, probably due to saliva clearance. Potentially, the probability that tonsillar crypts and the glottides will constantly harbour virions is greater than in other mucosal oral districts, and they will be detected with greater difficultly.

Is there any protein expression/overexpression which is strongly associated with HR HPV in HNC?

Our first thought regards p16 and indeed it has been recently proposed as a surrogate marker of HPV DNA infection for oropharyngeal cancers [32]. The results for OSCC are less definitive [33-37], although some recent studies performed by real-time PCR [38], tissue microarray [39] and on a mouse model [40] have revealed the ability to identify (due to an over-expression of p16) those OSCC in which HPV infection was biologically significant.

Does HPV positive oral cancer present a better prognosis and a different radio-chemo-sensitivity?

With reference to recent clinical data in the literature, HPV has been found to be the most significant positive prognostic factor in patients with oro-pharyngeal tumors, with a 60–80% reduction in the risk of death [41]. The favourable outcome of HPV-induced oropharyngeal cancers might be attributable to the absence of field cancerization or enhanced radiation sensitivity [42]. Taking this into consideration, the diagnosis of HPV infection should be determined in all oropharyngeal cancers, considering its presence as a key factor in the decision-making process of treatment [43-45]. However, we are unable to make the same suggestion for the OSCC. Furthermore, HPV 16 has been positively associated with a response to chemo-radiation in oro-pharyngeal cancer and with overall and disease-specific survival [46], whereas an HPV 16 positive cell line of HNSCC was recently found to be extremely cisplatinum-resistant [47].

How difficult is it to make a diagnosis of oral HPV infection?

When performing the molecular detection of HPV DNA from oral samples, attention should be focused on the low productivity of oral HPV infections. Indeed, studies based on polymerase chain reaction (PCR) assay have shown that, when compared to those from HPV-positive cervical specimens, HPV-DNA positive oral samples from both normal oral mucosa [13,48] and cancerous lesions [49] produce weaker PCR products. Based on such data, it is then essential that, in clinical and research HPV testing, all procedures employed are highly sensitive, specific and reliable. In addition, the aim of enhancing the standardization of the approach, in terms of the type of oral specimen examined, sampling method applied and HPV molecular assay employed, should be pursued. As far as the oral sample to be examined is concerned, both tissue samples and superficial cells have been evaluated in literature [48,50,51]. Biopsy tissue samples can be either frozen at -80°C and then minced without thawing for DNA analysis or they can be formalin-fixed and paraffin-embedded. Oral mucosa exfoliated cells can be obtained either by oral brushing or rinse, and advantages and disadvantages have been reported for each method. Tissue samples allow for the histo-pathological examination of the biopsies used for the HPV test, as well as permitting the in situ hybridization and localization of HPV DNA in infected cells. However, the highest rate of HPV DNA is reported in DNA from frozen tissue, but the value is much lower for paraffin-embedded tissue samples [48]. Oral scrapes or rinse samples, with their greater surface area of mucosa than with biopsies, are less invasive, and HR HPV detection in oral exfoliated cells is a reliable biomarker of an HPV-related HN cancer risk. A drawback is that not all patients who have HR-HPV types in oral exfoliated cells are detected with HPV DNA in the primary tumour [50]. However, if HPV testing of oral exfoliated cells has been selected, the use of oral rinses would appear more efficient, in terms of cell yield and DNA-containing nucleated cells, compared with the superficial brushing/scraping of oral mucosa (by using a cotton swab, wooden spatula or a cytobrush) [51,52]. Of the several mouthwashes tested in the literature, commercial mouthwashes (e.g., Cepacol®, Listermint®) would seem more efficient than sucrose, glucose and saline, in terms of DNA yield, quality and stability [53]. As far as HPV detection methods are concerned, it has been reported that methods such as Southern blotting and in situ hybridization should be avoided as they lead to lower HPV rates, compared with those obtained by using PCR assays [54,55].

As is the case with the most validated sampling procedures, it should be kept in mind that there are several other variables which may affect the efficiency and reliability of HPV detection in oral samples. For instance, the method of DNA purification also has a potentially large impact upon the ability to detect HPV DNA by PCR amplification [56]. Additionally, considerable differences exist regarding the use of different PCR primers. In the majority of the PCR-based HPV detection systems, a broad spectrum of HPV types is amplified by consensus primers, followed by detection with type-specific probes. The consensus primers may be either degenerate (as in the MY09/11 systems), or they may contain mismatches (as in the GP5+/6+ system), or they may contain inosine residues at ambiguous base positions (as in the SPF primers), or sets of overlapping primers (as in the PGMY primers). These methods have different analytical and clinical characteristics [57], and every method has its strengths and weakness. Although difficult to achieve, standardization and the use of validated procedures for HPV DNA is paramount in assisting physicians to provide more effective treatment and more efficient screening for patients.

What is the most common route of oral HPV transmission?

Even though modes of HPV transmission in the head and neck mucosal districts have not been fully resolved, theories have proposed multiple pathways for HPV transmission, including perinatal transmission, auto-infection from oral-genital contact by hand and sexual transmission by oral-genital contact. The perinatal transmission of HPV to neonates at birth has been detected in several studies which have demonstrated that recurrent respiratory papillomatosis is associated with the perinatal transmission of HPV. While the possibility of auto-infection among women with cervical HPV infection is still a matter of debate [52,58-60], oral sex, including fellatio and cunnilingus, has being hypothesized as being the main mode of transit for oral HPV infection. Recently, HPV was detected more commonly in biopsy specimens from cancer patients with more than one sexual partner and from those who practiced oral sex than in biopsy specimens from those who did not engage in oral sex, thereby confirming the possibility of oral transmission [61]. However, mouth-to-mouth transmission, for example through kissing, still remains possible and it should not be excluded as a route of oral HPV transmission. Since the onset of the HIV epidemic, an increase in oral sex among teenagers and young adults has been observed, probably because this is thought to represent a form of safe sex. However, oral sex is not free of risk and it can result in HPV-related cancer. Public education is of paramount importance: there is a need to disseminate these findings and to place them in context. Even though the transmission of genital HPV infection primarily occurs via sexual contact, HPV-related diseases such as condyloma acuminata and laryngeal papillomas occur in neonates and children [62], suggesting additional modes of viral transmission such as perinatal infection during the passage through an infected birth canal [63] and in utero, as a transplacental or ascending infection [64,65]. Caesarean deliveries do not protect neonates against HPV [66] and HPV infection may be associated with adverse pregnancy outcomes, including spontaneous preterm delivery [67].

Is HPV prevention possible and useful?

Although the use of condoms has proven efficient in the prevention of most sexually-transmitted infections, the effectiveness for prevention against HPV infection is not as clear, and a significant variability (from 0% to 80%) in the condom protection of HPV infection has been reported [68]. Alternatively, HPV infection could be prevented by the use of type-specific vaccines. In recent years, two HPV vaccines have been developed and are they available for primary vaccination in the European Union: a vaccine against HPV-16 and HPV-18 (Cervarix, produced by GlaxoSmithKline), which is administered in three doses (time 0, 1, and 6 months), and a quadrivalent vaccine against HPV-16, HPV-18, HPV-6 and HPV-11 (produced by Merck and distributed in Europe by Sanofi Pasteur MSD as Gardasil), which is administered in three doses (time 0, 2, and 6 months). The impressive range of protection, ranging from 86% to 100%, of the HPV vaccines has been recently reported [69,70]. The bivalent vaccine is advised for a reduction of precancerous cervical lesions and cancer incidence. In addition to cervical cancer prevention, the quadrivalent vaccine is advised for a reduction in genital condylomas. It is thought that these HPV vaccines could have broader implications, also for other HPV-related cancer in both women and men, thereby preventing oral as well as genital infections. This has prompted many researchers to advocate vaccinating boys as well as girls, with the bivalent vaccine to prevent HNC and by the tetravalent vaccine to additionally prevent oral condilomatosis. Thus, the question is "Can oropharyngeal cancer now be placed in the category of virally-mediated cancers?", like, for instance, HPV-related cervical, anal, vulvar, and penile cancers, or the Epstein Barr virus-associated nasopharyngeal cancers. Whilst it is premature to imagine an HPV vaccine which could protect women and men against HNC, the possibility that various oral, oro-pharyngeal, and laryngeal cancers might be prevented by HPV vaccination is certainly a hope, and this would bring forth significant implications from a public health perspective.

Beyond the vaccines, the potentiality of gene therapy

HPV vaccines should eventually reduce the impact of these viruses on human health. However, vaccines may not be useful for the treatment of existing disease, and it is necessary to develop effective therapies targeting those individuals who are already infected or are currently excluded from the first phase of a prophylactic vaccination program. Given the strong relationship between the expression of HPV E6 and E7 and cervical cancer carcinogenesis, many approaches have been directed against these oncogenes, for example, gene therapy for HPV-positive cervical cancers [71]. The different methods also include the treatment of cervical cancer with E6 short interfering RNA, the use of antisense RNA to E7 and E6 genes either alone or together, and the use of mutated E2 protein that acts as a cancer cell-specific inducer of apoptosis [72-74]. In in vitro studies on antisense HPV RNA transcripts, the transcripts of the E6 and E7 genes of HPV type 16 were introduced (via a recombinant adenoviral vector, e.g., Ad5CMV-HPV 16 AS) into human cervical cancer cells harbouring HPV 16; the effects of expression of these genes on cell and tumour growth were then analysed. It was found that, when E6 and E7 protein expression is suppressed, p53 and Rb protein expression increase, the Ad5CMV-HPV 16 AS-infected cells undergo apoptosis, and cell growth and tumourigenicity are greatly suppressed. However, even though gene therapy may prove to be beneficial in the treatment of cervical cancer and other HPV-induced diseases, a further understanding of the viral life cycle and the mechanisms underlying HPV-induced oncogenesis is necessary before this method could be employed for clinical use in humans.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

All authors read and approved the final manuscript.

References

  1. Parkin DM, Bray F, Ferlay JPP: Estimating the world cancer burden: Globocan 2000.

    Int J Cancer 2001, 94. PubMed Abstract | Publisher Full Text OpenURL

  2. Molinolo AA, Amornphimoltham P, Squarize CH, Castilho RM, Patel V, Gutkind JS: Dysregulated molecular networks in head and neck carcinogenesis.

    Oral Oncol 2008. PubMed Abstract | Publisher Full Text OpenURL

  3. Syrjanen KJ, Pyrhonen S, Syrjanen SM: Evidence suggesting human papillomavirus (HPV) etiology for the squamous cell papilloma of the paranasal sinus.

    Arch Geschwulstforsch 1983, 53:77-82. PubMed Abstract OpenURL

  4. Thompson IO, Bijl P, van Wyk CW, van Eyk AD: A comparative light-microscopic, electron-microscopic and chemical study of human vaginal and buccal epithelium.

    Arch Oral Biol 2001, 46:1091-1098. PubMed Abstract | Publisher Full Text OpenURL

  5. Shin KH, Min BM, Cherrick HM, Park NH: Combined effects of human papillomavirus-18 and N-methyl-N'-nitro-N-nitrosoguanidine on the transformation of normal human oral keratinocytes.

    Mol Carcinog 1994, 9:76-86. PubMed Abstract | Publisher Full Text OpenURL

  6. zur Hausen H, de Villiers EM, Gissmann L: Papillomavirus infections and human genital cancer.

    Gynecol Oncol 1981, 12:S124-128. PubMed Abstract | Publisher Full Text OpenURL

  7. Bosh FX, Lorincz A, Munoz N, Meijer CJ, Shah KV: The causal relation between human papillomavirus and cervical cancer.

    Journal of Clinical Pathology 2002, 55:244-265. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  8. Bouda M, Gorgoulis VG, Kastrinakis NG, Giannoudis A, Tsoli E, Danassi-Afentaki D, Foukas P, Kyroudi A, Laskaris G, Herrington CS, Kittas C: "High risk" HPV types are frequently detected in potentially malignant and malignant oral lesions, but not in normal oral mucosa.

    Mod Pathol 2000, 13:644-653. PubMed Abstract | Publisher Full Text OpenURL

  9. Scully C: Oral squamous cell carcinoma; from an hypothesis about a virus, to concern about possible sexual transmission.

    Oral Oncol 2002, 38:227-234. PubMed Abstract | Publisher Full Text OpenURL

  10. Orvidas LJ, Lewis JE, Olsen KD, Weiner JS: Intranasal verrucous carcinoma: relationship to inverting papilloma and human papillomavirus.

    Laryngoscope 1999, 109:371-375. PubMed Abstract | Publisher Full Text OpenURL

  11. McKay SP, Gregoire L, Lonardo F, Reidy P, Mathog RH, Lancaster WD: Human papillomavirus (HPV) transcripts in malignant inverted papilloma are from integrated HPV DNA.

    Laryngoscope 2005, 115:1428-1431. PubMed Abstract | Publisher Full Text OpenURL

  12. Terai M, Hashimoto K, Yoda K, Sata T: High prevalence of human papillomaviruses in the normal oral cavity of adults.

    Oral Microbiol Immunol 1999, 14:201-205. PubMed Abstract | Publisher Full Text OpenURL

  13. Giovannelli L, Campisi G, Lama A, Giambalvo O, Osborn J, Margiotta V, Ammatuna P: Human papillomavirus DNA in oral mucosal lesions.

    J Infect Dis 2002, 185:833-836. PubMed Abstract | Publisher Full Text OpenURL

  14. Kreimer AR, Clifford GM, Boyle P, Franceschi S: Human papillomavirus types in head and neck squamous cell carcinomas worldwide: a systematic review.

    Cancer Epidemiol Biomarkers Prev 2005, 14:467-475. PubMed Abstract | Publisher Full Text OpenURL

  15. Gillison ML, Koch WM, Capone RB, Spafford M, Westra WH, Wu L, Zahurak ML, Daniel RW, Viglione M, Symer DE, Shah KV, Sidransky D: Evidence for a causal association between human papillomavirus and a subset of head and neck cancers.

    J Natl Cancer Inst 2000, 92:709-720. PubMed Abstract | Publisher Full Text OpenURL

  16. Syrjanen K, Syrjanen S, Lamberg M, Pyrhonen S, Nuutinen J: Morphological and immunohistochemical evidence suggesting human papillomavirus (HPV) involvement in oral squamous cell carcinogenesis.

    Int J Oral Surg 1983, 12:418-424. PubMed Abstract | Publisher Full Text OpenURL

  17. Herrero R, Castellsague X, Pawlita M, Lissowska J, Kee F, Balaram P, Rajkumar T, Sridhar H, Rose B, Pintos J, Fernández L, Idris A, Sánchez MJ, Nieto A, Talamini R, Tavani A, Bosch FX, Reidel U, Snijders PJ, Meijer CJ, Viscidi R, Muñoz N, Franceschi S, IARC Multicenter Oral Cancer Study Group: Human papillomavirus and oral cancer: the International Agency for Research on Cancer multicenter study.

    J Natl Cancer Inst 2003, 95:1772-1783. PubMed Abstract | Publisher Full Text OpenURL

  18. Syrjanen S: HPV infections and tonsillar carcinoma.

    J Clin Pathol 2004, 57:449-455. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  19. Gillison ML: Human papillomavirus-associated head and neck cancer is a distinct epidemiologic, clinical, and molecular entity.

    Semin Oncol 2004, 31:744-754. PubMed Abstract | Publisher Full Text OpenURL

  20. Pintos J, Black MJ, Sadeghi N, Ghadirian P, Zeitouni AG, Viscidi RP, Herrero R, Coutlee F, Franco EL: Human papillomavirus infection and oral cancer: a case-control study in Montreal, Canada.

    Oral Oncol 2008, 44:242-250. PubMed Abstract | Publisher Full Text OpenURL

  21. Andrews E, Seaman WT, Webster-Cyriaque J: Oropharyngeal carcinoma in non-smokers and non-drinkers: A role for HPV.

    Oral Oncol 2008. PubMed Abstract | Publisher Full Text OpenURL

  22. Sugiyama M, Bhawal UK, Dohmen T, Ono S, Miyauchi M, Ishikawa T: Detection of human papillomavirus-16 and HPV-18 DNA in normal, dysplastic, and malignant oral epithelium.

    Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003, 95:594-600. PubMed Abstract | Publisher Full Text OpenURL

  23. Zhang ZY, Sdek P, Cao J, Chen WT: Human papillomavirus type 16 and 18 DNA in oral squamous cell carcinoma and normal mucosa.

    Int J Oral Maxillofac Surg 2004, 33:71-74. PubMed Abstract | Publisher Full Text OpenURL

  24. Dahlstrom KR, Adler-Storthz K, Etzel CJ, Liu Z, Dillon L, El-Naggar AK, Spitz MR, Schiller JT, Wei Q, Sturgis EM: Human papillomavirus type 16 infection and squamous cell carcinoma of the head and neck in never-smokers: a matched pair analysis.

    Clin Cancer Res 2003, 9:2620-2626. PubMed Abstract | Publisher Full Text OpenURL

  25. Ritchie JM, Smith EM, Summersgill KF, Hoffman HT, Wang D, Klussmann JP, Turek LP, Haugen TH: Human papillomavirus infection as a prognostic factor in carcinomas of the oral cavity and oropharynx.

    Int J Cancer 2003, 104:336-344. PubMed Abstract | Publisher Full Text OpenURL

  26. Termine N, Panzarella V, Falaschini S, Russo A, Matranga D, Lo Muzio L, Campisi G: HPV in oral squamous cell carcinoma vs head and neck squamous cell carcinoma biopsies: a meta-analysis (1988–2007).

    Ann Oncol 2008, 19:1681-1690. PubMed Abstract | Publisher Full Text OpenURL

  27. Snijders PJ, Steenbergen RD, Heideman DA, Meijer CJ: HPV-mediated cervical carcinogenesis: concepts and clinical implications.

    J Pathol 2006, 208:152-164. PubMed Abstract | Publisher Full Text OpenURL

  28. Syrjanen S, Shabalova I, Petrovichev N, Podistov J, Ivanchenko O, Zakharenko S, Nerovjna R, Kljukina L, Branovskaja M, Juschenko A, Tosi P, Syrjänen K, NIS Cohort Study Group: Age-specific incidence and clearance of high-risk human papillomavirus infections in women in the former Soviet Union.

    Int J STD AIDS 2005, 16:217-223. PubMed Abstract | Publisher Full Text OpenURL

  29. Munoz N, Bosch FX, de Sanjose S, Herrero R, Castellsague X, Shah KV, Snijders PJ, Meijer CJ: Epidemiologic classification of human papillomavirus types associated with cervical cancer.

    N Engl J Med 2003, 348:518-527. PubMed Abstract | Publisher Full Text OpenURL

  30. Burd EM: Human papillomavirus and cervical cancer.

    Clin Microbiol Rev 2003, 16:1-17. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  31. Herrero R, Hildesheim A, Bratti C, Sherman ME, Hutchinson M, Morales J, Balmaceda I, Greenberg MD, Alfaro M, Burk RD, Wacholder S, Plummer M, Schiffman M: Population-based study of human papillomavirus infection and cervical neoplasia in rural Costa Rica.

    J Natl Cancer Inst 2000, 92:464-474. PubMed Abstract | Publisher Full Text OpenURL

  32. Begum S, Gillison ML, Ansari-Lari MA, Shah K, Westra WH: Detection of human papillomavirus in cervical lymph nodes: a highly effective strategy for localizing site of tumor origin.

    Clin Cancer Res 2003, 9:6469-6475. PubMed Abstract | Publisher Full Text OpenURL

  33. Nemes JA, Deli L, Nemes Z, Marton IJ: Expression of p16(INK4A), p53, and Rb proteins are independent from the presence of human papillomavirus genes in oral squamous cell carcinoma.

    Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006, 102:344-352. PubMed Abstract | Publisher Full Text OpenURL

  34. Greer RO Jr, Meyers A, Said SM, Shroyer KR: Is p16(INK4a) protein expression in oral ST lesions a reliable precancerous marker?

    Int J Oral Maxillofac Surg 2008, 37:840-846. PubMed Abstract | Publisher Full Text OpenURL

  35. Lim KP, Hamid S, Lau SH, Teo SH, Cheong SC: HPV infection and the alterations of the pRB pathway in oral carcinogenesis.

    Oncol Rep 2007, 17:1321-1326. PubMed Abstract | Publisher Full Text OpenURL

  36. Cunningham LL Jr, Pagano GM, Li M, Tandon R, Holm SW, White DK, Lele SM: Overexpression of p16INK4 is a reliable marker of human papillomavirus-induced oral high-grade squamous dysplasia.

    Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006, 102:77-81. PubMed Abstract | Publisher Full Text OpenURL

  37. Fregonesi PA, Teresa DB, Duarte RA, Neto CB, de Oliveira MR, Soares CP: p16(INK4A) immunohistochemical overexpression in premalignant and malignant oral lesions infected with human papillomavirus.

    J Histochem Cytochem 2003, 51:1291-1297. PubMed Abstract | Publisher Full Text OpenURL

  38. Weinberger PM, Yu Z, Haffty BG, Kowalski D, Harigopal M, Brandsma J, Sasaki C, Joe J, Camp RL, Rimm DL, Psyrri A: Molecular classification identifies a subset of human papillomavirus – associated oropharyngeal cancers with favorable prognosis.

    J Clin Oncol 2006, 24:736-747. PubMed Abstract | Publisher Full Text OpenURL

  39. Konig F, Krekeler G, Honig JF, Cordon-Cardo C, Fischer G, Korabiowska M: Relation between human papillomavirus positivity and p16 expression in head and neck carcinomas – a tissue microarray study.

    Anticancer Res 2007, 27:283-288. PubMed Abstract OpenURL

  40. Strati K, Pitot HC, Lambert PF: Identification of biomarkers that distinguish human papillomavirus (HPV)-positive versus HPV-negative head and neck cancers in a mouse model.

    Proc Natl Acad Sci USA 2006, 103:14152-14157. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  41. Psyrri A, DiMaio D: Human papillomavirus in cervical and head-and-neck cancer.

    Nat Clin Pract Oncol 2008, 5:24-31. PubMed Abstract | Publisher Full Text OpenURL

  42. Lindel K, Beer KT, Laissue J, Greiner RH, Aebersold DM: Human papillomavirus positive squamous cell carcinoma of the oropharynx: a radiosensitive subgroup of head and neck carcinoma.

    Cancer 2001, 92:805-813. PubMed Abstract | Publisher Full Text OpenURL

  43. Klozar J, Kratochvil V, Salakova M, Smahelova J, Vesela E, Hamsikova E, Betka J, Tachezy R: HPV status and regional metastasis in the prognosis of oral and oropharyngeal cancer.

    Eur Arch Otorhinolaryngol 2008, 265:S75-82. PubMed Abstract | Publisher Full Text OpenURL

  44. Reimers N, Kasper HU, Weissenborn SJ, Stutzer H, Preuss SF, Hoffmann TK, Speel EJ, Dienes HP, Pfister HJ, Guntinas-Lichius O, Klussmann JP: Combined analysis of HPV-DNA, p16 and EGFR expression to predict prognosis in oropharyngeal cancer.

    Int J Cancer 2007, 120:1731-1738. PubMed Abstract | Publisher Full Text OpenURL

  45. Kumar B, Cordell KG, Lee JS, Worden FP, Prince ME, Tran HH, Wolf GT, Urba SG, Chepeha DB, Teknos TN, Eisbruch A, Tsien CI, Taylor JM, D'Silva NJ, Yang K, Kurnit DM, Bauer JA, Bradford CR, Carey TE: EGFR, p16, HPV Titer, Bcl-xL and p53, sex, and smoking as indicators of response to therapy and survival in oropharyngeal cancer.

    J Clin Oncol 2008, 26:3128-3137. PubMed Abstract | Publisher Full Text OpenURL

  46. Kumar B, Cordell KG, Lee JS, Prince ME, Tran HH, Wolf GT, Urba SG, Worden FP, Chepeha DB, Teknos TN, Eisbruch A, Tsien CI, Taylor JM, D'Silva NJ, Yang K, Kurnit DM, Bradford CR, Carey TE: Response to therapy and outcomes in oropharyngeal cancer are associated with biomarkers including human papillomavirus, epidermal growth factor receptor, gender, and smoking.

    Int J Radiat Oncol Biol Phys 2007, 69:S109-111. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  47. Hoffmann TK, Sonkoly E, Hauser U, van Lierop A, Whiteside TL, Klussmann JP, Hafner D, Schuler P, Friebe-Hoffmann U, Scheckenbach K, Erjala K, Grénman R, Schipper J, Bier H, Balz V: Alterations in the p53 pathway and their association with radio- and chemosensitivity in head and neck squamous cell carcinoma.

    Oral Oncol 2008, 44:1100-1109. PubMed Abstract | Publisher Full Text OpenURL

  48. Ostwald C, Muller P, Barten M, Rutsatz K, Sonnenburg M, Milde-Langosch K, Loning T: Human papillomavirus DNA in oral squamous cell carcinomas and normal mucosa.

    J Oral Pathol Med 1994, 23:220-225. PubMed Abstract | Publisher Full Text OpenURL

  49. Snijders PJ, Scholes AG, Hart CA, Jones AS, Vaughan ED, Woolgar JA, Meijer CJ, Walboomers JM, Field JK: Prevalence of mucosotropic human papillomaviruses in squamous-cell carcinoma of the head and neck.

    Int J Cancer 1996, 66:464-469. PubMed Abstract | Publisher Full Text OpenURL

  50. Smith EM, Ritchie JM, Summersgill KF, Hoffman HT, Wang DH, Haugen TH, Turek LP: Human papillomavirus in oral exfoliated cells and risk of head and neck cancer.

    J Natl Cancer Inst 2004, 96:449-455. PubMed Abstract | Publisher Full Text OpenURL

  51. Lawton G, Thomas S, Schonrock J, Monsour F, Frazer I: Human papillomaviruses in normal oral mucosa: a comparison of methods for sample collection.

    J Oral Pathol Med 1992, 21:265-269. PubMed Abstract | Publisher Full Text OpenURL

  52. Smith EM, Ritchie JM, Yankowitz J, Wang D, Turek LP, Haugen TH: HPV prevalence and concordance in the cervix and oral cavity of pregnant women.

    Infect Dis Obstet Gynecol 2004, 12:45-56. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  53. Heath EM, Morken NW, Campbell KA, Tkach D, Boyd EA, Strom DA: Use of buccal cells collected in mouthwash as a source of DNA for clinical testing.

    Arch Pathol Lab Med 2001, 125:127-133. PubMed Abstract | Publisher Full Text OpenURL

  54. Ha PK, Pai SI, Westra WH, Gillison ML, Tong BC, Sidransky D, Califano JA: Real-time quantitative PCR demonstrates low prevalence of human papillomavirus type 16 in premalignant and malignant lesions of the oral cavity.

    Clin Cancer Res 2002, 8:1203-1209. PubMed Abstract | Publisher Full Text OpenURL

  55. Kay P, Meehan K, Williamson AL: The use of nested polymerase chain reaction and restriction fragment length polymorphism for the detection and typing of mucosal human papillomaviruses in samples containing low copy numbers of viral DNA.

    J Virol Methods 2002, 105:159-170. PubMed Abstract | Publisher Full Text OpenURL

  56. D'Souza G, Sugar E, Ruby W, Gravitt P, Gillison M: Analysis of the effect of DNA purification on detection of human papillomavirus in oral rinse samples by PCR.

    J Clin Microbiol 2005, 43:5526-5535. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  57. Brink AA, Snijders PJ, Meijer CJ: HPV detection methods.

    Dis Markers 2007, 23:273-281. PubMed Abstract | Publisher Full Text OpenURL

  58. Kellokoski J, Syrjanen S, Yliskoski M, Syrjanen K: Dot blot hybridization in detection of human papillomavirus (HPV) infections in the oral cavity of women with genital HPV infections.

    Oral Microbiol Immunol 1992, 7:19-23. PubMed Abstract | Publisher Full Text OpenURL

  59. Kellokoski JK, Syrjanen SM, Chang F, Yliskoski M, Syrjanen KJ: Southern blot hybridization and PCR in detection of oral human papillomavirus (HPV) infections in women with genital HPV infections.

    J Oral Pathol Med 1992, 21:459-464. PubMed Abstract | Publisher Full Text OpenURL

  60. Giraldo P, Goncalves AKS, Pereira SA, Barros-Mazon S, Gondo ML, Witkin SS: Human papillomavirus in the oral mucosa of women with genital human papillomavirus lesions.

    Eur J Obstet Gynecol Reprod Biol 2006, 126:104-106. PubMed Abstract | Publisher Full Text OpenURL

  61. Gillison ML, Koch WM, Shah KV: Human papillomavirus in head and neck squamous cell carcinoma: are some head and neck cancers a sexually transmitted disease?

    Curr Opin Oncol 1999, 11:191-199. PubMed Abstract | Publisher Full Text OpenURL

  62. Silverberg MJ, Thorsen P, Lindeberg H, Grant LA, Shah KV: Condyloma in pregnancy is strongly predictive of juvenile-onset recurrent respiratory papillomatosis.

    Obstet Gynecol 2003, 101:645-652. PubMed Abstract | Publisher Full Text OpenURL

  63. Rintala MA, Grenman SE, Puranen MH, Isolauri E, Ekblad U, Kero PO, Syrjanen SM: Transmission of high-risk human papillomavirus (HPV) between parents and infant: a prospective study of HPV in families in Finland.

    J Clin Microbiol 2005, 43:376-381. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  64. Tseng CJ, Liang CC, Soong YK, Pao CC: Perinatal transmission of human papillomavirus in infants: relationship between infection rate and mode of delivery.

    Obstet Gynecol 1998, 91:92-96. PubMed Abstract | Publisher Full Text OpenURL

  65. Medeiros LR, Ethur AB, Hilgert JB, Zanini RR, Berwanger O, Bozzetti MC, Mylius LC: Vertical transmission of the human papillomavirus: a systematic quantitative review.

    Cad Saude Publica 2005, 21:1006-1015. PubMed Abstract | Publisher Full Text OpenURL

  66. Sarkola ME, Grenman SE, Rintala MA, Syrjanen KJ, Syrjanen SM: Human papillomavirus in the placenta and umbilical cord blood.

    Acta Obstet Gynecol Scand 2008, 87:1181-1188. PubMed Abstract | Publisher Full Text OpenURL

  67. Gomez LM, Ma Y, Ho C, McGrath CM, Nelson DB, Parry S: Placental infection with human papillomavirus is associated with spontaneous preterm delivery.

    Hum Reprod 2008, 23:709-715. PubMed Abstract | Publisher Full Text OpenURL

  68. Manhart LE, Koutsky LA: Do condoms prevent genital HPV infection, external genital warts, or cervical neoplasia? A meta-analysis.

    Sex Transm Dis 2002, 29:725-735. PubMed Abstract | Publisher Full Text OpenURL

  69. Garland SM, Hernandez-Avila M, Wheeler CM, Perez G, Harper DM, Leodolter S, Tang GW, Ferris DG, Steben M, Bryan J, Taddeo FJ, Railkar R, Esser MT, Sings HL, Nelson M, Boslego J, Sattler C, Barr E, Koutsky LA, Females United to Unilaterally Reduce Endo/Ectocervical Disease (FUTURE) I Investigators: Quadrivalent vaccine against human papillomavirus to prevent anogenital diseases.

    N Engl J Med 2007, 356:1928-1943. PubMed Abstract | Publisher Full Text OpenURL

  70. Harper DM, Franco EL, Wheeler CM, Moscicki AB, Romanowski B, Roteli-Martins CM, Jenkins D, Schuind A, Costa Clemens SA, Dubin G: Sustained efficacy up to 4.5 years of a bivalent L1 virus-like particle vaccine against human papillomavirus types 16 and 18: follow-up from a randomised control trial.

    Lancet 2006, 367:1247-1255. PubMed Abstract | Publisher Full Text OpenURL

  71. Yamato K, Yamada T, Kizaki M, Ui-Tei K, Natori Y, Fujino M, Nishihara T, Ikeda Y, Nasu Y, Saigo K, Yoshinouchi M: New highly potent and specific E6 and E7 siRNAs for treatment of HPV16 positive cervical cancer.

    Cancer Gene Ther 2008, 15:140-153. PubMed Abstract | Publisher Full Text OpenURL

  72. Green KL, Brown C, Roeder GE, Southgate TD, Gaston K: A cancer cell-specific inducer of apoptosis.

    Hum Gene Ther 2007, 18:547-561. PubMed Abstract | Publisher Full Text OpenURL

  73. Green KL, Southgate TD, Mulryan K, Fairbairn LJ, Stern PL, Gaston K: Diffusible VP22-E2 protein kills bystander cells and offers a route for cervical cancer gene therapy.

    Hum Gene Ther 2006, 17:147-157. PubMed Abstract | Publisher Full Text OpenURL

  74. Jonson AL, Rogers LM, Ramakrishnan S, Downs LS Jr: Gene silencing with siRNA targeting E6/E7 as a therapeutic intervention in a mouse model of cervical cancer.

    Gynecol Oncol 2008, 111:356-364. PubMed Abstract | Publisher Full Text OpenURL