Rising prevalence of human papillomavirus related oropharyngeal cancer in Australia over the last 2 decades

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1 ORIGINAL ARTICLE Rising prevalence of human papillomavirus related oropharyngeal cancer in Australia over the last 2 decades Angela Hong, PhD, 1,2 * C. Soon Lee, MD, 1,3 Deanna Jones, BAppSci, 4 Anne-Sophie Veillard, MS, 5 Mei Zhang, MD, 1,2 Xiaoying Zhang, PhD, 1 Robert Smee, MBBS, 6 June Corry, MBBS, 7 Sandro Porceddu, MBBS, 8 Christopher Milross, MD, 1,2 Michael Elliott, MPhil, 9 Jonathan Clark, MBBS, 1,9 Barbara Rose, PhD 4 1 Central Clinical School, The University of Sydney, Sydney, New South Wales, Australia, 2 Department of Radiation Oncology, Lifehouse, Sydney, New South Wales, Australia, 3 Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Sydney, New South Wales, Australia, 4 Department of Infectious Diseases and Immunology, The University of Sydney, Sydney, New South Wales, Australia, 5 NHMRC Clinical Trials Centre, The University of Sydney, Sydney, New South Wales, Australia, 6 Department of Radiation Oncology, Prince of Wales Hospital, Randwick, New South Wales, Australia, 7 Division of Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia, 8 Cancer Services, Princess Alexandra Hospital, University of Queensland, Brisbane, Queensland, Australia, 9 Sydney Head and Neck Cancer Institute, Royal Prince Alfred Hospital, Sydney, New South Wales, Australia. Accepted 10 December 2014 Published online 25 June 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI /hed ABSTRACT: Background. This study provides Australian data on the characteristics of human papillomavirus (HPV)-related oropharyngeal squamous cell carcinoma (SCC) over the last 2 decades. Methods. The HPV status of 515 patients with oropharyngeal SCC diagnosed between 1987 and 2010 was determined by HPV E6-targeted multiplex real time polymerase chain reaction assay (PCR) and p16 immunohistochemistry. Results. The HPV positivity rate increased from 20.2% ( ) to 63.5% ( ). Among HPV-positive oropharyngeal SCC over the study period, the median age increased from 55.4 years to 59.8 years (p 5.004) and there was a trend of an increasing proportion of never smokers (19.2% to 34.0%). The use of radiation therapy (RT) in patients with HPV-positive oropharyngeal cancer increased from 26.9% to 68.1% (p 5.007) and we also observed a trend of improved outcomes. Conclusion. Our data show a rising prevalence of HPV-positive oropharyngeal SCC in Australia over the last 2 decades. These patients with HPV-positive oropharyngeal SCC are now presenting at an older age and about one third have never smoked. VC 2015 Wiley Periodicals, Inc. Head Neck 38: , 2016 KEY WORDS: human papillomavirus (HPV), oropharyngeal cancer, head and neck cancer INTRODUCTION Head and neck squamous cell carcinoma is the sixth most common cancer worldwide 1 and the incidence of oropharyngeal squamous cell carcinoma (SCC) is increasing in Western countries despite declining tobacco use. 2 6 We have previously reported that this increase in Australia is likely attributable to a rise in the proportion of oropharyngeal SCC caused by human papillomavirus (HPV); from 19% ( ) to 47% ( ) to 66% ( ). 3 This trend is particularly apparent in the younger age group and parallels findings in other developed countries where HPV positivity rates as high as 72% have been reported. 7 The biological characteristics of HPV-positive oropharyngeal SCC are distinct from those of HPV-negative oropharyngeal SCC with respect to expression of the p16ink4a (p16), and genetic profiles, including the frequency of mutations in the p53 gene. 8,9 Epidemiologically, *Corresponding author: A. Hong, Central Clinical School, The University of Sydney, Level 6, Blackburn Building, New South Wales, 2006 Australia. angela.hong@sydney.edu.au Contract grant sponsor: This study was supported by a grant from the Cure Cancer Australia. it has been reported that patients with HPV-positive oropharyngeal SCC tend to be younger, less likely to have a history of tobacco and alcohol use, and tend to have a higher number of sexual partners, in particular oral sexual partners, than patients with HPV-negative oropharyngeal SCC. 10 Furthermore, HPV-positive oropharyngeal SCC is associated with markedly better survival, despite a tendency for higher grade and more advanced nodal disease. 11 This study extends our previous work 3 by including patients treated for oropharyngeal SCC at 10 large teaching hospitals in Australia over the last 2 decades. We sought evidence of change in HPV status relative to tobacco exposure, personal characteristics, treatment patterns, and outcomes over the study period. The purpose of this study was to gain new insight into the changing epidemiology of oropharyngeal SCC in Australia. MATERIALS AND METHODS Incidence of oropharyngeal cancer in Australia Cancer incidence data were obtained from the National Cancer Statistics Clearing House database of the Australian Institute of Health and Welfare (AIHW; gov.au), which incorporates data from the 8 Australian HEAD & NECK DOI /HED MAY

2 HONG ET AL. TABLE 1. Patient characteristics by human papillomavirus status. Characteristic HPV-positive (n 5 220) HPV-negative (n 5 295) p value for heterogeneity Age at diagnosis, y (mean, range) 55.8 (31 89) 61 (39 83) <.0001 Sex.6336 Female 49 (22.3%) 71 (24.1%) Male 171 (77.7%) 224 (75.9%) Smoking status <.0001 Nonsmoker 59 (26.8%) 14 (4.7%) Ex-smoker 86 (39.1%) 90 (30.5%) Current smoker 75 (34.1%) 191 (64.7%) Alcohol status (missing 5 77).0148 Nondrinker 32 (17.4%) 21 (8.3%) Ex-drinker 15 (8.2%) 25 (9.8%) Drinker 137 (74.5%) 208 (81.9%) Primary tumor site.0009 Tonsil 181 (82.3%) 222 (75.3%) Base of tongue 29 (13.2%) 30 (10.2%) Other oropharyngeal 10 (4.5%) 43 (14.6%) Grade < (9.1%) 60 (20.3%) 2 76 (34.5%) 161 (54.6%) (56.4%) 74 (25.1%) T classification (missing 5 2) (25.1%) 32 (10.9%) 2 77 (35.2%) 107 (36.4%) 3 56 (25.6%) 104 (35.4%) 4 31 (14.2%) 51 (17.3%) N classification (missing 5 4) < (20.9%) 146 (50.2%) 1 38 (17.3%) 61 (21.0%) (50.9%) 71 (24.4%) 3 24 (10.9%) 13 (4.5%) TNM classification (missing 5 1) < (2.7%) 26 (8.8%) 2 18 (8.2%) 63 (21.4%) 3 47 (21.4%) 92 (31.3%) (67.7%) 113 (38.4%) Abbreviation: HPV, human papillomavirus. state and territory cancer registries. We used the data for oropharyngeal SCC incorporating the base of tongue (C01), tonsil (C09), and other sites within the oropharynx (C10) and laryngeal cancer as a smoking-related head and neck cancer for comparison. Study population The study cohort comprised 520 consecutive patients with primary oropharyngeal SCC treated with curative intent at 10 hospitals in Australia between 1987 and The study was approved by Sydney Local Health Service Ethics committees (Protocol x ). The oropharynx is defined as palatine tonsil (tonsillar fossa, tonsillar pillar), base of tongue, soft palate, and posterior walls of the oropharynx. Patient selection was based on the availability of tumor and clinicopathological data. The HPV status of the oropharyngeal SCC was not determined at the time of diagnosis and therefore treatment decisions were not based on HPV status. Laboratory studies An HPV-positive tumor was defined as one testing positive for both HPV DNA and p16 expression to ensure virus causality. 12 Presence and type of HPV DNA were determined on two to six 4 to 5 mm sections of formalin-fixed paraffin-embedded tumor using an HPV E6-based multiplex real time polymerase chain reaction assay (PCR) modified from Stanley and Szewczuk. 13 This assay detects and identifies 21 HPV types (16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66, 68, 70, 73, 82, 53, 6, 11, and 26). Stringent precautions were taken to avoid cross-contamination and water blanks placed after every fifth tube to detect contamination. DNA was extracted using the QIAmp RNA viral mini kit (Qiagen, 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 C.S.L. in hematoxylin-eosin stained sections cut after those for HPV analysis. Expression of p16 was determined by semiquantitative immunohistochemistry using an autostainer (Dako, Australia), the JC2 clone (Neomarkers, USA) (1/200) and the EnVision Flex Dual Link horseradish peroxidase/dab visualization system (Dako, Australia). Staining was evaluated by 2 investigators, including a pathologist, as per our established protocol. 14 Statistical analyses Associations between HPV status and clinicopathological characteristics were assessed using a 2-sample t test 744 HEAD & NECK DOI /HED MAY 2016

3 RISING PREVALENCE OF HPV-RELATED OROPHARYNGEAL CANCER FIGURE 1. (A) Locoregional recurrence. (B) Event free survival (C) Overall survival. HPV, human papillomavirus. for the continuous variable and chi-square tests for categorical variables. The time trend in the proportion of oropharyngeal cancers testing HPV-positive was analyzed using the binary test for trend. Times to locoregional failure, death from oropharyngeal cancer, and death from any cause were calculated from the date of diagnosis. Locoregional recurrence was defined as clinical, radiological, and/or pathological evidence of recurrence at the primary site or in the regional nodal area. The Kaplan Meier method was used to construct time-to-event curves. RESULTS Patient characteristics This 23-year study was divided into 4 periods (1995 and prior, , , and ). Five patients with HPV DNA-positive but p16-negative oropharyngeal SCC were excluded from the analysis. The characteristics of the 515 patients included in the study are shown in Table 1. Overall 220 of the 515 patients (42.7%) had HPV-positive oropharyngeal SCC. There was a gradual increase in the prevalence of HPV-positive oropharyngeal SCC from 20.2% in the 1987 to 1995 period to 63.5% in the 2006 to 2010 period. At diagnosis, patients with HPV-positive oropharyngeal SCC were significantly younger, more likely to be never smokers and nondrinkers, and to have a tonsillar primary, lower T stage and higher N stage (hence, higher TNM stage; FIGURE 2. (A) Incidence of oropharyngeal cancer in Australia from 1991 to 2009 (from Australian Institute of Health and Welfare [AIHW]). (B) Incidence of laryngeal cancer in Australia from 1991 to 2009 (from AIHW). HEAD & NECK DOI /HED MAY

4 HONG ET AL. TABLE 2. The baseline characteristics of patients with HPV-positive tumors by study period. All years (n 5 220) Before 1995 (n 5 26) (n 5 80) (n 5 67) (n 5 47) p value for heterogeneity (p value for trend) Mean age at diagnosis, y (range) 55.8 (31 89) 55.4 (34 77) 52 (31 76) 57.0 (35 89) 59.8 (32 86).0040 (.003) Sex.9267 Female 49 (22.3%) 6 (23.1%) 19 (23.8%) 13 (19.4%) 11 (23.4%) (.86) Male 171 (77.7%) 20 (76.9%) 61 (76.3%) 54 (80.6%) 36 (76.6%) Smoking status.6101 Non smoker 59 (26.8%) 5 (19.2%) 18 (22.5%) 20 (29.9%) 16 (34.0%) (.19) Ex-smoker 86 (39.1%) 12 (46.2%) 31 (38.8%) 28 (41.8%) 15 (31.9%) Current smoker 75 (34.1%) 9 (34.6%) 31 (38.8%) 19 (28.4%) 16 (34.0%) Alcohol status (missing 5 36).5574 Non smoker 32 (17.4%) 6 (28.6%) 8 (13.8%) 13 (21.3%) 5 (11.4%) (.63) Ex-drinker 15 (8.2%) 1 (4.8%) 4 (6.9%) 5 (8.2%) 5 (11.4%) Drinker 137 (74.5%) 14 (66.7%) 46 (79.3%) 43 (70.5%) 34 (77.3%) Primary tumor site.0058 Tonsil 181 (82.3%) 21 (80.8%) 70 (87.5%) 57 (85.1%) 33 (70.2%) Base of tongue 29 (13.2%) 4 (15.4%) 6 (7.5%) 5 (7.5%) 14 (29.8%) Other oropharyngeal 10 (4.5%) 1 (3.8%) 4 (5.0%) 5 (7.5%) 0 (0.0%) Grade (9.1%) 3 (11.5%) 9 (11.3%) 4 (6.0%) 4 (8.5%) (.11) 2 76 (34.5%) 10 (38.5%) 29 (36.3%) 25 (37.3%) 12 (25.5%) (56.4%) 13 (50.0%) 42 (52.5%) 38 (56.7%) 31 (66.0%) T classification (missing 5 1) (25.1%) 5 (19.2%) 13 (16.5%) 20 (29.9%) 17 (36.2%) (.001) 2 77 (35.2%) 9 (34.6%) 25 (31.6%) 24 (35.8%) 19 (40.4%) 3 56 (25.6%) 8 (30.8%) 24 (30.4%) 18 (26.9%) 6 (12.8%) 4 31 (14.2%) 4 (15.4%) 17 (21.5%) 5 (7.5%) 5 (10.6%) N classification (20.9%) 5 (19.2%) 21 (26.3%) 11 (16.4%) 9 (19.1%) (.67) 1 38 (17.3%) 4 (15.4%) 17 (21.3%) 10 (14.9%) 7 (14.9%) (50.9%) 13 (50.0%) 32 (40.0%) 39 (58.2%) 28 (59.6%) 3 24 (10.9%) 4 (15.4%) 10 (12.5%) 7 (10.4%) 3 (6.4%) TNM classification (2.7%) 2 (7.7%) 2 (2.5%) 1 (1.5%) 1 (2.1%) (.20) 2 18 (8.2%) 1 (3.8%) 7 (8.8%) 4 (6.0%) 6 (12.8%) 3 47 (21.4%) 6 (23.1%) 23 (28.8%) 12 (17.9%) 6 (12.8%) (67.7%) 17 (65.4%) 48 (60.0%) 50 (74.6%) 34 (72.3%) Treatment.0068 RT (1/- CTX) 112 (50.9%) 7 (26.9%) 42 (52.5%) 31 (46.3%) 32 (68.1%) (.007) Surgery 1/- adjuvant RT (1/- CTX) 108 (49.1%) 19 (73.1%) 38 (47.5%) 36 (53.7%) 15 (31.9%) Abbreviations: RT, radiotherapy; CTX, chemotherapy. Table 1). The median follow-up of the whole cohort was 48.5 months and 233 patients had died at the time of last follow-up. Patients with HPV-positive oropharyngeal SCC had significantly better outcomes in terms of locoregional recurrence, event-free survival, and overall survival (Figure 1A 1C). Increasing incidence of oropharyngeal squamous cell carcinoma in Australia Data from AIHW showed that the incidence of oropharyngeal SCC in Australia doubled from 322 cases per year in 1991 to 665 cases per year in 2009 (Figure 2A). This increase was seen in both sexes but was more apparent in men (from 235 cases in 1991 to 530 cases in 2009). In comparison, the incidence of laryngeal SCC (a smoking-related head and neck cancer) was stable in both men and women during the same period (Figure 2B). Time trends by human papillomavirus status Among patients with HPV-positive oropharyngeal SCC, the median age increased from 55.4 years in the 1987 to 1995 period to 59.8 years in the 2006 to 2010 period (p 5.004; Table 2). The proportion that was never smokers at the time of diagnosis increased from 19.2% (1995 and prior) to 34.0% ( ; p value for trend 5.19 for never smokers vs ex-smokers vs current smokers and p value for trend 5.08 for never smokers vs smokers). Over time, patients with HPV-positive oropharyngeal SCC were also more likely to have base of tongue primary sites (15.4% vs 29.8%; p 5.006) and lower T classification (in the more recent study period [19.2% vs 36.2%; p 5.069]). In patients with HPV-negative oropharyngeal SCC, there was no significant difference in the median age at diagnosis, the proportion of nonsmokers (4.7%), the location of the primary site, or T classification over the study period (Table 3). 746 HEAD & NECK DOI /HED MAY 2016

5 RISING PREVALENCE OF HPV-RELATED OROPHARYNGEAL CANCER TABLE 3. The baseline characteristics of patients with HPV-negative tumors by study period. Characteristic All years (n 5 295) Before 1995 (n 5 103) (n 5 94) (n 5 71) (n 5 27) p value for heterogeneity (p value for trend) Mean age at diagnosis, y 61.0 (39 83) 59.5 (42 77) 61.7 (39 82) 61.2 (41 83) 63.3 (45 82).1748 (.059) Gender.2122 Female 71 (24.1%) 32 (31.1%) 20 (21.3%) 13 (18.3%) 6 (22.2%) (.088) Male 224 (75.9%) 71 (68.9%) 74 (78.7%) 58 (81.7%) 21 (77.8%) Smoking status.7311 Non smoker 14 (4.7%) 5 (4.9%) 2 (2.1%) 5 (7.0%) 2 (7.4%) (.38) Ex-smoker 90 (30.5%) 28 (27.2%) 32 (34.0%) 22 (31.0%) 8 (29.6%) Current smoker 191 (64.7%) 70 (68.0%) 60 (63.8%) 44 (62.0%) 17 (63.0%) Alcohol status (missing 5 41).0197 Non drinker 21 (8.3%) 9 (10.3%) 3 (3.8%) 7 (11.1%) 2 (8.0%) (.22) Ex-drinker 25 (9.8%) 6 (6.9%) 9 (11.4%) 3 (4.8%) 7 (28.0%) Drinker 208 (81.9%) 72 (82.8%) 67 (84.8%) 53 (84.1%) 16 (64.0%) Primary tumor site.4650 Tonsil 222 (75.3%) 78 (75.7%) 75 (79.8%) 51 (71.8%) 18 (66.7%) Base of tongue 30 (10.2%) 11 (10.7%) 10 (10.6%) 7 (9.9%) 2 (7.4%) Other oropharyngeal 43 (14.6%) 14 (13.6%) 9 (9.6%) 13 (18.3%) 7 (25.9%) Grade (20.3%) 26 (25.2%) 18 (19.1%) 11 (15.5%) 5 (18.5%) (.071) (54.6%) 54 (52.4%) 54 (57.4%) 41 (57.7%) 12 (44.4%) 3 74 (25.1%) 23 (22.3%) 22 (23.4%) 19 (26.8%) 10 (37.0%) T classification (missing 5 1) (10.9%) 15 (14.6%) 8 (8.6%) 4 (5.6%) 5 (18.5%) (.37) (36.4%) 38 (36.9%) 29 (31.2%) 30 (42.3%) 10 (37.0%) (35.4%) 39 (37.9%) 39 (41.9%) 19 (26.8%) 7 (25.9%) 4 51 (17.3%) 11 (10.7%) 17 (18.3%) 18 (25.4%) 5 (18.5%) N classification (missing 5 4) (50.2%) 60 (58.3%) 45 (48.4%) 30 (43.5%) 11 (42.3%) (.073) 1 61 (21.0%) 20 (19.4%) 18 (19.4%) 16 (23.2%) 7 (26.9%) 2 71 (24.4%) 19 (18.4%) 22 (23.7%) 23 (33.3%) 7 (26.9%) 3 13 (4.5%) 4 (3.9%) 8 (8.6%) 0 (0.0%) 1 (3.8%) TNM classification (missing 5 1) (8.8%) 14 (13.6%) 6 (6.5%) 2 (2.8%) 4 (14.8%) (.048) 2 63 (21.4%) 24 (23.3%) 18 (19.4%) 16 (22.5%) 5 (18.5%) 3 92 (31.3%) 36 (35.0%) 29 (31.2%) 19 (26.8%) 8 (29.6%) (38.4%) 29 (28.2%) 40 (43.0%) 34 (47.9%) 10 (37.0%) Treatment.9142 RT (1/- CTX) 126 (42.7%) 42 (40.8%) 41 (43.6%) 30 (42.3%) 13 (48.1%) (.58) Surgery 1/- adjuvant RT (1/- CTX) 169 (57.3%) 61 (59.2%) 53 (56.4%) 41 (57.7%) 14 (51.9%) Abbreviations: RT, radiotherapy; CTX, chemotherapy. Treatment over the study period There was an increase in the use of definitive radiation therapy (RT; with or without chemotherapy) and a decrease in the use of surgery (with or without adjuvant therapy) over the study period (p ). Overall, RT was used in 27.6% of patients in the earliest period (1995 and prior), but the rate had more than doubled (58.6%) by the latest period ( ). This increase was seen only in patients with HPV-positive oropharyngeal SCC, 26.9% in the 1987 to 1995 period to 68.1% in the 2006 to 2010 period (p 5.007). In contrast, there was no significant change in the treatment approach in patients with HPV-negative oropharyngeal SCC (p 5.914). Outcomes over the study period During the 23-year study period, there was a trend toward better locoregional control in patients with HPVpositive oropharyngeal SCC (p 5.075; Figure 3A). Similarly, the event-free survival and overall survival also improved in the more recent study periods (Figure 3B and 3C). However, the outcomes of patients with HPVnegative oropharyngeal SCC did not change during the study period (Figure 4). DISCUSSION This study has provided new insight into the changing epidemiology of oropharyngeal SCC in Australia. Data collected from more than 500 patients treated at 10 teaching hospitals in Australia over the last 2 decades showed a steady increase in the proportion of HPV-positive oropharyngeal SCC (from 20.2% to 63.5% over the study period). This is consistent with our earlier smaller series 3 and parallels findings from other developed countries. 2,15 18 Overall results strongly support the concept HEAD & NECK DOI /HED MAY

6 HONG ET AL. FIGURE 3. Outcomes of patients with human papillomavirus (HPV)-positive oropharyngeal squamous cell carcinoma (SCC) over the 4 study periods ( and prior; ; ; and ). (A) Locoregional recurrence. (B) Event-free survival. (C) Overall survival. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] that HPV accounts for the increasing incidence of oropharyngeal SCC seen in Australia and in other developed countries. 18,19 The effect of declining tobacco use in our community on the epidemiology of oropharyngeal SCC was a major focus of this study. Many studies have shown that patients with HPV-positive oropharyngeal SCC are less likely to have a history of tobacco use than those with HPV-negative oropharyngeal SCC. 20,21 In our cohort, patients with HPV-positive oropharyngeal SCC were increasingly likely to be never smokers at diagnosis (from 19.2% to 34.0% over the study period). Our current rate of never smokers with HPV-positive oropharyngeal SCC is similar to that reported from other Western countries. 20,22 The role of mutagens in tobacco as a co-factor to HPV in the development of oropharyngeal SCC, and the interaction between HPV and smoking in prognosis and response to treatment are not fully understood. Previous studies have shown that among patients with HPVpositive oropharyngeal SCC, smokers had poorer outcomes than never smokers. 21,23 Our findings have important research and public health implications. However, smoking remains a major risk factor for oropharyngeal SCC worldwide, underscoring the need for prevention strategies targeted toward tobacco and alcohol use. Interestingly, the median age at diagnosis for our patients with HPV-positive oropharyngeal SCC increased over time. We speculate that this could be related to the declining proportion of smokers in this cohort, therefore less exposure to the potential co-carcinogen tobacco. Overall, the median age of patients with HPV-positive oropharyngeal SCC was still less than that of patients with HPV-negative oropharyngeal SCC. HPV-negative oropharyngeal SCC has traditionally been associated with tobacco use (and alcohol abuse), and smoking patterns among this group did not change over time, with only about 5% being never smokers, 30% ex-smokers, and 60% current smokers at the time of diagnosis. In line with our previous studies 24,25 and other published data, 26 the tonsil was the predominant primary site for HPV-positive oropharyngeal SCC. Interestingly, the proportion of base of tongue primaries increased over time and there was also a trend for lower T stage at presentation. Further longitudinal studies will be needed to 748 HEAD & NECK DOI /HED MAY 2016

7 RISING PREVALENCE OF HPV-RELATED OROPHARYNGEAL CANCER FIGURE 4. Outcomes of patients with human papillomavirus (HPV)-negative oropharyngeal squamous cell carcinoma (SCC) over the 4 study periods ( and prior; ; ; and ). (A) Locoregional recurrence. (B) Event-free survival. (C) Overall survival. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] confirm these trends and to identify underlying factors. This study found no evidence of changes in the epidemiology of HPV-negative oropharyngeal SCC over the study period. It is unlikely that the difference in HPV prevalence in the different periods is due to a different analytical sensitivity of our HPV DNA PCR in different periods as the cycle threshold values did not differ between the years. We also tested for p16 expression with immunohistochemistry, which our controls have shown is unaffected by sample DNA quality. P16 is a cyclin-dependent kinase inhibitor and is induced as a consequence of inhibition of retinoblastoma protein activity by the HPV E7 oncoprotein. The reason for the rapid increase in prevalence of HPV-positive oropharyngeal SCCs remains elusive. One explanation may be a change in sexual behavior (ie, the increasing practice of oral sex and increasing numbers of lifetime sex partners). Data from Europe and the United States suggest that the number of lifetime sexual partners has increased over recent decades. 27,28 As the HPV infection usually takes more than 10 years to progress from infection to malignancy, a temporal change in sexual behavior could explain the increased incidence observed in HPV-positive oropharyngeal SCC. There is a geographic variation in terms of incidence rates of oropharyngeal SCC. 10 This likely reflects wide variability in the prevalence of established risk behaviors and modifiers. Our study lacks details of sexual activity, drug use, and socioeconomic status to show any change in these risk factors during the study period. Although HPV vaccination offers the potential to stem this trend, it will not have an impact on the incidence of HPV-positive oropharyngeal SCC for decades. Given the rising trends and the approximately 40-year lag time between infection and manifestation of the disease, HPVpositive oropharyngeal SCC will be a problem for the foreseeable future. In the interim, the HPV-positive oropharyngeal SCC epidemic will have tremendous implications for health care resources; these typically younger, healthier patients have a high chance of surviving their disease, 23 and they will have to live with the late effects of treatment for many decades. Our results showed a trend in improved outcomes in patients with HPV-positive oropharyngeal SCC over the HEAD & NECK DOI /HED MAY

8 HONG ET AL. study period but not in patients with HPV-negative oropharyngeal SCC. This could be the result of the increasing use of combined chemotherapy and RT, but our data do not allow us to draw definitive conclusions on the best treatment for patients with HPV-positive oropharyngeal SCC. The choice of treatment in our study cohort was not based on the HPV status (the HPV status was not available in the majority) and the increasing use of RT was only seen in the patients with HPV-positive oropharyngeal SCC. This is likely because of their younger age and higher nodal stage at diagnosis. Given the favorable prognosis in this cohort, assessment of the HPV status of oropharyngeal SCC should be routine in clinical practice. However, the best treatment regimen for HPV-positive oropharyngeal SCC has not been defined and tremendous interest has been expressed in deescalating therapy to decrease toxicity. Potential deescalation strategies include the use of transoral robotic surgery, reduced doses of radiation or chemotherapy (or both), or avoidance of chemotherapy entirely for low-risk patients. One such trial is the TROG study, which aims to compare the treatment-related side effects of RT with concurrent cisplatin or cetuximab regimens in HPV-positive oropharyngeal SCC. In conclusion, our data show a rising prevalence of HPV-positive oropharyngeal SCC in Australia over the last 2 decades, from 20.2% (1995 and prior) to 63.5% ( ). These patients with HPV-positive oropharyngeal SCC are now presenting at an older age and about one-third have never smoked. Acknowledgments The authors thank the clinicians at all the participating hospitals. REFERENCES 1. Parkin DM, Bray F, Ferlay J, Pisani P. Global cancer statistics, CA Cancer J Clin 2005;55: Chaturvedi AK, Engels EA, Anderson WF, Gillison ML. 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