Stringent precautions were taken to avoid cross-contamination find more and water blanks placed after every fifth tube to detect contamination. DNA was extracted using the QIAmp RNA viral mini kit (Qiagen, Hilden, Germany). Measured amounts of equine herpesvirus were used to monitor DNA extraction efficiency and removal of PCR inhibitors. The presence of cancer cells was confirmed by pathologist CSL in H&E-stained sections cut after those for HPV analysis. Expression

of p16 was determined by semiquantitative immunohistochemistry using an autostainer (Dako Carpinteria), the JC2 clone (Neomarkers, Fremont, CA) (1/200) and the EnVision™ Flex Dual Link horseradish peroxidise/DAB visualisation system (Dako). Staining was evaluated by two investigators including pathologist CSL. Associations between HPV status and clinicopathological characteristics were assessed using a two-sample t-test for the continuous variable age and Chi-squared tests for categorical variables. Analyses were conducted using the SAS System for Windows (SAS Institute, MLN0128 purchase Cary NC, USA) and Stata Statistical Software (Stata Corporation: College Station, TX, USA). The time trend in the proportion of oropharyngeal cancers testing HPV-positive was analysed using the Chi-squared test for trend. p16 staining was strong, nuclear and cytoplasmic and essentially all

or none (Fig. 1). Weak focal staining was regarded as negative. Overall, 110 of the 302 oropharyngeal tumours (36%) were HPV DNA-positive/p16-positive with HPV 16 alone or with other types in 100 (91%) and HPV 18 alone in 3 (3%). 98 of the 110 HPV-positive cases (89%) contained only vaccine targets (types 16, 18). HPV type distribution in relation to HPV DNA and p16 status is shown in Table 2. Thirty-four (11%) tumours testing HPV DNA-positive/p16-negative were

regarded as HPV-negative since evidence of virus activity is needed for virus Tolmetin causality [13]. These results were confirmed on repeat p16 and HPV DNA testing and Ct scores in the tandem HPV DNA assay indicated low copy number. The proportion of samples without evidence of active virus was lower than in some previous studies [13]. Two HPV-negative/p16-positive tumours were excluded from analyses, resulting in a final total of 300. The HPV-positivity rate increased between 1987 and 2005 (1987–1990: 19%, 1991–1995:22%, 1996–2000: 40%, 2001–2005: 47%), P for trend = 0.002 and by 2005–2006 had risen to 66%. Data on associations between HPV and age, gender, stage and grade are presented in Table 1. Based on Australian Institute of Health and Welfare data 2001–2005, our HPV-positivity rate in that period of 47% (HPV 16 alone 85%, HPV 18 alone 3% and both HPV 16 and 18 1%), on average, up to 156 new cases of oropharyngeal cancer (age-standardised rate 1.56 per 100,000 males) per year were potentially preventable by vaccinating males.