br Introduction br Numerous infectious viruses and bacteria
Numerous infectious viruses and bacteria are established risk factors for certain cancers (International Agency for Research on Cancer, 2012). Many carcinogenic infections are strongly associated with spe-cific cancers (e.g., Helicobacter pylori (H. pylori) and non-cardia gastric cancer, HBX-41108 virus (HBV) and hepatitis C virus (HCV) and hepa-tocellular carcinoma) (Helicobacter and Cancer Collaborative Group, 2001; Cho et al., 2011), while several others are necessary causes for
Globally, almost one-sixth of cancers were attributable to infections with large geographical variations observed (de Martel et al., 2012; Parkin, 2006; Plummer et al., 2016). The proportion of infection-at-tributable cancers in 2012 varied from a high 31.3% in Sub-Saharan Africa to a low 4.0% in North America (Plummer et al., 2016). Although the latter constitutes a relatively smaller percentage, there is an
Corresponding author at: Division of Cancer Epidemiology, McGill University, 5100 Maisonneuve Blvd West, Suite 720, Montréal, Québec H4A 3T2, Canada. E-mail address: [email protected] (K.D. Volesky).
1 Additional ComPARe Study Team members: Stephen Walter, Department of Health Research Methods, Evidence, and Impact, McMaster University, Hamilton, Ontario, Canada; Will King, Department of Public Health Sciences, Queen’s University, Kingston, Ontario, Canada; Paul Demers, Occupational Cancer Research Centre, Toronto, Ontario, Canada; Paul Villeneuve, Department of Health Sciences, Carleton University, Ottawa, Ontario, Canada; Prithwish De, Cancer Care Ontario, Toronto, Ontario, Canada; Leah Smith, Canadian Cancer Society, Toronto, Ontario, Canada; Abbey Poirier, Department of Cancer Epidemiology and Prevention research, CancerControl Alberta, Alberta Health Services, Calgary, Alberta, Canada; Elizabeth Holmes, Canadian Cancer Society, Toronto, Ontario, Canada; Dylan O'Sullivan, Department of Public Health Sciences, Queen's University, Kingston, Ontario, Canada; Zeinab El-Masri, Cancer Care Ontario, Toronto, Ontario, Canada; Robert Nuttall, Canadian Cancer Society, Toronto, Ontario, Canada; Sheila Bouten, Division of Cancer Epidemiology, McGill University, Montréal, Québec, Canada; Tasha Narain, Department of Public Health Sciences, Queen's University, Kingston, Ontario, Canada; Priyanka Gogna, Department of Public Health Sciences, Queen's University, Kingston, Ontario, Canada.
opportunity to lower the Canadian cancer burden with currently available interventions. Specifically, primary preventive interventions include vaccination against HBV and HPV, along with secondary pre-vention measures such as direct-acting antivirals for chronic HCV in-fection and antibiotic therapy to treat H. pylori infection (De Flora and Bonanni, 2011; Falade-Nwulia et al., 2017; Kohli et al., 2014). The prolonged latency associated with HCV and H. pylori provides an op-portunity to treat them prior to cancer development (Lingala and Ghany, 2015).
Although, to date, no study has estimated the impact of the different infections on cancer incidence in Canada, a global study reported that 3.9% of incident cancers in Canada were attributable to infections overall in 2012 (Plummer et al., 2016). The global analysis combined infection prevalence for regions comprising many countries; for ex-ample, low, medium and high infection incidence areas. Since infection prevalence varies geographically, region-specific data based on more recent evidence from the scientific literature and population-based studies are necessary to obtain accurate estimates of the impact of in-fections on cancer incidence. Additionally, estimating individually the proportion of cancers attributable to each infection provides essential assessment of the cancer burden due to infections with modifiable prevalence.
Overview of the carcinogenic infections and associated cancer sites.a
Estimates of the impact of each infection on cancer incidence will contribute to the evidence needed to prioritize strategies aimed at re-ducing the prevalence of certain carcinogenic infections and initiating treatment for others. We estimated, among individuals 18 years and older, the proportion and number of cancers diagnosed in Canada in 2015 that were attributable to infections, by sex and age whenever possible.
The current analysis is part of the ComPARe (Canadian population attributable risk of cancer) Study, which estimates the current and fu-ture burden of cancer due to modifiable risk factors in Canada. Here, we estimated the current burden of cancers caused by infections.
2.1. Infections and cancer sites selection
We considered infections classified by the International Agency for Research on Cancer (IARC) as established, Group 1, carcinogens (Table 1). Infections with extremely low prevalence in Canada (Opis-thorchis viverrini, Clonorchis sinensis, and Schistosoma haematobium) were excluded. We also did not include human immunodeficiency virus