Human papillomavirus type 16 is episomal and a high viral load may be correlated to better prognosis in tonsillar cancer

Abstract

The aim of our study was to investigate the physical state and the viral load of HPV-16 in tonsillar cancer and to correlate these findings with clinical outcome. To distinguish between integrated and episomal forms of HPV, 22 freshfrozen tonsillar cancer samples were analysed by a method based on restriction enzyme cleavage, ligation and PCR (rliPCR). HPV-16 was detected in 11/22 and HPV-33 in 1/22 of the cancers, hence 12/22 (55%) of the tumours were HPV positive. Only extrachromosomal forms of HPV-16 were observed. Full-length episomal HPV was detected exclusively in 7/11 of the cancers, whereas both full-length and deleted forms of episomal HPV-16 were found in parallel in 2 other tumours. In 1 tumour only a deleted episomal form of HPV-16 was present. In the remaining HPV-16 positive tumour both full-length episomal as well as an 11 kbp PCR product were detected and if the 11 kbp product contained integrated HPV, or was off-size linearised episomal could not be determined. In 2 cervical cancer controls, HPV-16 was integrated and could be chromosome located. HPV-16 was quantified by real-time PCR and most tonsillar cancers contained between 10 to a few hundred copies of HPV per ␤-actin. Key words: HPV; tonsillar cancer; physical state; viral load; prognosisAccumulating molecular and epidemiological data indicate that the high-risk types of human papillomavirus (HPV) are not only associated with cervical cancer, but may also be associated with certain subtypes of cancer in the head and neck. [1][2][3][4][5] The strongest association has been found for oropharyngeal squamous cell carcinoma, especially tonsillar cancer, where HPV DNA is present in 45-70% of the cases. [1][2][3][5][6][7][8][9] In a nested case-control study it was found that patients who were sero-positive for HPV-16 had a 14.4 excess risk of developing oropharyngeal cancer later in life, and in another study patients with a history of HPV-related anogenital cancer had a 4.3 higher risk of developing tonsillar cancer. 4,10 Furthermore, patients with HPV positive tonsillar cancer seem less likely to be heavy smokers and drinkers, and to have a better prognosis than patients with HPV negative tonsillar cancer. 3,7,8 Similar to cervical cancer, the oncogenes of HPV-16, E6 and E7, are generally expressed in HPV positive tonsillar cancer. 1,9,11,12 The viral protein E6 promotes degradation of p53, whereas E7 inactivates pRb. 13,14 P53 mutations have been reported to be less frequent in HPV positive tonsillar cancer as compared to HPV negative tonsillar cancer, although when assayed by immunohistochemistry the proportion of elevated p53 levels are similar in both HPV positive and negative tumours. 3,12,15 In addition, HPV positive tonsillar cancers seem to have a decrease of pRb, possibly due to E7 activity. 2,9 In cervical cancer the HPV genome is mainly integrated in the host genome. 16,17 Integration leads to disruption and deletion of the viral genes E1 or E2 open reading frame (ORF), which are of importance for viral replication and viral transc...

P21Cip1/WAF1 expression is strongly associated with HPV-positive tonsillar carcinoma and a favorable prognosis

“…Other strong indicators for a favorable prognosis in our study include tumor diameter o4 cm, low/no expression of cyclin D1, and low/no tobacco consumption. In accordance with most other studies on HPV-related oropharyngeal carcinomas, we also found a favorable disease-specific survival in patients with HPV16-positive tonsillar squamous cell carcinomas, 12,46,[60][61][62][63][64] and p14 ARF overexpression, 31 although with less significance than the indicators described above. We noticed that lymph node status, which is generally considered as the most important prognostic factor in head-and-neck squamous cell carcinomas, 23 had little value in our series of tonsillar squamous cell carcinomas, which is in concordance with other studies.…”

HPV16 semiquantitative viral load and serologic biomarkers in oral and oropharyngeal squamous cell carcinomas

“…27 Most of these studies employed the gold-standard for HPV viral load assessment: real-time PCR. 27,28 However, based on this study, it seems that the less costly, more feasible semiquantitative method may also have utility in epidemiologic studies in which laborious real-time PCR assays may not be possible. Important limitations may exist for both semiquantitative and quantitative viral load assessment.…”

Biology of Human Papillomavirus Infections in Head and Neck Carcinogenesis

“…The HPV copy numbers found in HNSCCs are often lower than detected in cervical cancers. Among HNSCC, the highest copy numbers are detected in palatine tonsillar cancers and the best survival figures are reported to those tonsillar cancers harboring the highest copy numbers and episomal form of HPV [52]. As discussed earlier, not all HPV genomes are replicating in the cells.…”

“…The HPV types have also been grouped into mucosal or cutaneous types, based on their tropism for specific epithelial sites. Mucosal HPV types found preferentially in precancerous and cancerous lesions have been designated as 'high-risk' types and these include types 16,18,31,33,34,35,39,45,51,52,56,58,59, 66, 68, and 70. Mucosal HPVs found in benign genital warts and other non-malignant lesions are generally labeled as 'low-risk' types, the most important ones being HPV 6,11,42,43, and 44 [1,2].…”