Highlights
- Approximately 4% of new cancers diagnosed in Ontario in 2013 resulted from infections.
- Cancers caused by infections in Ontario are mostly preventable by known methods.
- There is potential to improve prevention strategies around infections and cancer, particularly for infections with human papillomavirus, Helicobacter pylori, hepatitis C virus, and hepatitis B virus.
According to a recently released report, Burden of Cancer Caused by Infections in Ontario, approximately 4% of new cancers diagnosed in Ontario in 2013 resulted from infections, most of which are preventable or treatable.[1] Of the approximately 3,100 cancer cases (plausible range 2,443 to 3,591) from cancer-causing infections, most were due to human papillomavirus (HPV), Helicobacter pylori (H. pylori), hepatitis C virus (HCV), Epstein-Barr virus (EBV) and hepatitis B virus (HBV).
Because HPV, H. pylori, HCV and HBV account for a large number of cancer cases in Ontario, the best way to reduce the cancer burden from infections is to improve their prevention and treatment. There are no known ways to prevent infection with EBV or the cancers associated with it.
HPV is a common sexually transmitted virus strongly associated with cervical cancer, anal cancer and other cancers, including oropharyngeal.[2] In 2013, HPV was responsible for 1,365 (plausible range 1,281 to 1,447) new cancers in Ontario. Current prevention efforts for HPV and its associated cancers include organized cervical cancer screening and vaccinating Grade 7 students and men up to age 26 who have sex with men. The number of HPV infections and their associated cancers are expected to decrease in future as a result of HPV vaccination. More HPV-associated cancers could be prevented by expanding the publicly funded vaccination program to include more of the people recommended by the National Advisory Committee on Immunization.[3] For example, the vaccine could be provided at an earlier age, to a broader age range and with an extended catch-up period for those who miss a dose. Other possible ways to improve prevention include the rapid adoption of new vaccines that become available and increasing awareness of vaccine availability. Cancer prevention opportunities related to screening include public education about its importance, the future integration of HPV testing into cervical screening and possibly screening for other associated cancers.
H. pylori is a bacteria that infects the stomach and is passed from person to person through contaminated saliva, feces and water, or during medical procedures.[2] People who are infected with H. pylori have an increased risk of developing stomach cancer (non-cardia gastric cancer and gastric non-Hodgkin lymphoma).[4][5]In 2013, H. pylori infection was responsible for over 1,000 (plausible range 759 to 1,229) new cancers in Ontario. Infection with H. pylori is treatable; however, screening at the population level is not done due to concerns about antibiotic resistance and because there is not enough evidence showing that it is effective in regions where there is a low rate of infection, such as Ontario.[6][7]Prevention of H. pylori-associated cancers may improve when more is known about the pattern of infection in Ontario, who is most likely to benefit from treatment, and when the results of treatment trials become available.[8]
HCV is a virus that causes liver inflammation and is transmitted by exposure to infected blood.[9] People with chronic HCV infection have a much higher risk of liver cancer and a greater chance of developing non-Hodgkin lymphoma.[10][11]In 2013, HCV was responsible for 293 (plausible range 113 to 430) new cancers in Ontario. Current efforts to limit transmission include testing the blood supply, treating infections and implementing harm reduction programs. Improvements in the early detection and treatment of HCV infections and promoting the screening of high risk groups[10]by primary care providers could lower the number of cancers associated with HCV infection.
Infection with HBV also causes liver inflammation and is transmitted through exposure to infected blood and bodily fluids. People with chronic HBV infection have an increased risk of developing liver cancer.[11] In 2013, HBV was responsible for 137 (plausible range 68 to 206) new liver cancers in Ontario. Current efforts to prevent transmission include the school-based immunization program, sexual health education and testing the blood supply. Prevention opportunities include monitoring the vaccination program’s effectiveness and making changes as required,[12] screening children of families that immigrated from endemic countries before they are vaccinated, offering HBV treatment more widely, and following up with people who have come into contact with those infected.
More information on these infections and the cancers they cause can be found in the Burden of Cancer Caused by Infections in Ontario report. The report describes the epidemiology and distribution of cancers associated with infections in Ontario, quantifies the burden of cancer from all cancer-causing infections that are prevalent in Ontario, and describes efforts and opportunities to prevent cancers associated with infections. It is hoped that the report will serve as a baseline for measuring policy change over time, inform Ontario-specific cancer prevention programs and policies, and help prioritize areas for future prevention efforts.