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Evidence-based insights on 3 types of cancer screening

The Bottom Line

  • Globally, cancer is a leading cause of death.
  • Cancer screening tools aim to help detect cancer early, thereby increasing the chances of treatment success.
  • The Canadian Preventive Taskforce does not recommend the use of the prostate-specific antigen (PSA) test as a screening tool for prostate cancer.
  • The US Preventive Services Task Force does not recommend ovarian cancer screening for women at “average risk” for ovarian cancer and who have no symptoms.
  • Mammography reduces the risk of death from breast cancer in women aged 50 to 69 years who are at average risk for breast cancer, but the findings for those less than 50 years old and over 70 years old are not conclusive.   
  • In general, men and women are advised to speak with their health care team about their personal risk for cancer and options for screening and collaborate on a screening plan that makes sense for them.  

Cancer is a major contributor to illness and mortality worldwide (1). However, catching cancer early can increase the chance of successfully treating it. One strategy for early diagnosis is screening. The purpose of screening is to detect abnormalities that point to the potential presence of cancer or pre-cancer prior to the individual starting to experience symptoms (1). Sounds optimal, right? The answer is yes, but only for some. As with many things in life, there is no “one-size-fits-all” model when it comes to screening. The decision of whether to screen or not to screen depends on weighing the benefits and harms for individuals or groups (2-5). But what does the research have to say about different forms of cancer screening? Here are just a few of the evidence-based insights on screening for prostate cancer, ovarian cancer, and breast cancer. Click on the links below to learn more.


1. Screening for prostate cancer

Prostate-specific antigen (PSA) is a protein produced by the prostate cells. The PSA test is used to assess the level of PSA in the blood, with high levels of PSA eluding to the potential presence of prostate cancer. Despite the wide-use of this test as a method for prostate cancer screening, it is not deemed very reliable, and the Canadian Preventive Taskforce does not recommend its use as a screening tool. In particular, the PSA test is not advised for use in men under 55 and over 70 years of age, while those aged 55 to 69 (the highest risk group) are directed to speak with a health professional about available screening options prior to opting for a PSA test. Why is that? Well, the benefits of the PSA test are not consistent, but the harms—including false positive results, complications associated with further tests undertaken to help reach a diagnosis (e.g., biopsies), and overdiagnosis—are noteworthy (2;3). These results relate to men who do not have symptoms of prostate cancer prior to screening. It is also important to mention that recommendations around using or not using PSA tests are not agreed upon by all experts (6).


2. Screening for ovarian cancer

Transvaginal ultrasounds and/or cancer antigen 125 (CA-125) blood tests are two methods used to screen for ovarian cancer (4;7). The ultrasound takes images of the ovaries, while the blood test looks for high levels of the CA-125 protein. Research shows that ovarian cancer screening does not decrease deaths from ovarian cancer in women who are over the age of 45, symptomless, and at “average risk” of the disease. However, false positive test results have the potential to lead to unnecessary surgeries in this population (4). As such, both the US Preventive Services Task Force and the Canadian Preventive Taskforce do not recommend ovarian cancer screening in women with an “average risk” of ovarian cancer who do not have symptoms (4;7-8).


3. Screening for breast cancer

Mammography—or a mammogram—involves taking x-ray images of the breasts to screen for breast cancer (5;9-10). In women at “average risk” for breast cancer, mammography reduces the risk of death in those aged 50 to 69 years, but not in those under 50 years old and between 70 and 74 years old. With that said, the findings for the under 50 and between 70 and 74 age groups are not as conclusive. What’s more, mammography, may also increase the risk of overdiagnosis in women under 50 years of age, as well as those between 50 and 69 years of age (4). Similar to PSA tests, varying opinions exist around the use mammography, specifically on issues such as which groups should be screened and when to initiate screening (4;11-13).


Please note that the results for ovarian and breast cancer screening  are only relevant to people at "average risk" of those  cancers, and NOT high risk folks, while the results for prostate cancer screening are relevant to men without symptoms of prostate cancer.  


Next to steps for you

You might be thinking, “What does this mean for me?” and no one would blame you. Between some inconclusive results, differing findings by age group, and mixed-messaging by experts, it can be hard to tease out what is best for you. The good news is you do not have to figure it all out on your own. Decisions around whether to screen, which screening option is best for you, and how to go about it should be made in consultation with your health care team. Together you can assess your level of risk, weigh the benefits and harms for you as an individual, and incorporate your preferences. 


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References

  1. World Health Organization. Cancer. [Internet] 2021. [cited September 2021]. Available from https://www.who.int/news-room/fact-sheets/detail/cancer
  2. Bell N, Gorber S, Shane A et al. Recommendations on screening for prostate cancer with the prostate-specific antigen test. CMAJ. 2014; 186:1225-34. doi: 10.1503/cmaj.140703. 
  3. Fenton JJ, Weyrich MS, Durbin S, et al. Prostate-specific antigen-based screening for prostate cancer: Evidence report and systematic review for the US Preventive Services Task Force. JAMA. 2018; 319(18):1914-1931. doi: 10.10001/jama.2018.3712. 
  4. Henderson JT, Webber EM, Sawaya GF. Screening for ovarian cancer: Updated evidence report and systematic review for the US Preventive Services Task Force. JAMA. 2018; 319:595-606. doi: 10.1001/jama.2017.21421. 
  5. Canelo-Aybar C, Ferreira DS, Ballesteros M, et al. Benefits and harms of breast cancer mammography screening for women at average risk of breast cancer: A systematic review for the European Commission Initiative on Breast Cancer. J Med Screen. 2021. doi: 10.1177/0969141321993866.
  6. Gulati R, Tsodikov A, Etzioni R, et al. Expected population impacts of discontinued prostate-specific antigen screening. Cancer. 2014; 120:3519–3526. doi: 10. 1002/cncr.28932.
  7. Grossman DC, Curry SJ, Owens DK, et al. Screening for Ovarian Cancer: US Preventive Services Task Force recommendation statement. JAMA. 2018; 319(6):588-594. doi: 10.1001/jama.2017.21926.
  8. Canadian Task Force on Preventative Health Care. Ovarian cancer. [Internet] 2019. [cited September 2021]. Available  https://canadiantaskforce.ca/guidelines/appraised-guidelines/ovarian-cancer/  
  9. Canadian Cancer Society. Screening for breast cancer. [Internet] 2021. [cited September 2021]. Available from https://cancer.ca/en/cancer-information/cancer-types/breast/screening  
  10. Canadian Task Force on Preventive Health Care. Breast Cancer Update (2018). [Internet] 2019. [cited September 2021]. Available from https://canadiantaskforce.ca/guidelines/published-guidelines/breast-cancer-update/   
  11. WHO position paper on mammography screening. Geneva: World health Organisation, 2014.
  12. Tonelli M, Gorber SC, Joffres M, et al. Recommendations on screening for breast cancer in average-risk women aged 40-74 years. Canad Med Assoc J. 2011; 183:1991-2001. doi: 10.1503/cmaj.110334. 
  13. Oeffinger KC, Fontham ET, Etzioni R, American Cancer Society, et al. Breast cancer screening for women at average risk: 2015 guideline update from the American cancer society. JAMA. 2015; 314: 1599-1614. doi: 10.1001/jama.2015.12783. 

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