How are Benefits and Harms Presented in US Cancer Screening and Prevention Guidelines?

A recent study published in the Journal of the National Cancer Institute in the US examined the way that potential benefits and potential harms arising from cancer screening programs are presented in cancer screening guidelines published for use by doctors in the US.

It is almost certain that the findings of this study will apply in Australia as well. While many cancer screening programs have been in place for many years, it is only recently that people have begun to assess how many people are harmed rather than receive a benefit from participating in a cancer screening program.

There are multiple ways that people can be harmed by cancer screening programs. In some cases, the screening test itself may cause harm, for example when a colonoscopy causes a tear in the person’s bowel. However most screening tests are relatively harmless like having a blood test, a cervical smear or an imaging test. However, a positive screening test will almost inevitably lead to more invasive and dangerous test like having tissue biopsies taken. This second investigation may or may not be positive, the frequency of positive second-line tests depends on the false-positive rate of the first screening test.

The biopsy may be diagnosed as malignant and thus the person will be diagnosed with cancer. Unfortunately, at present we can’t differentiate the smaller proportion of cancers that will turn out to be harmless from those that will progress and may eventually kill the patient. Some cancers behave in way that is called “indolent”, that is they grow very slowly and will never cause problems within that person’s lifetime. Some true cancers spontaneously remit, that is they go away by themselves. However, nearly everyone diagnosed with cancer will receive treatment and cancer treatment is often unpleasant and dangerous in itself and may have many different types of side-effects that affect the person’s quality of life.

Given the above it would be reasonable to expect that cancer screening guidelines should present a balanced view of the potential harms as well as the potential benefits that a person may expect from cancer screening. The authors looked at guidelines published by a number of different bodies including the United States Preventive Services Task Force, the American Cancer Society, the American College of Physicians and the National Comprehensive Cancer Network. They found that almost seventy percent of cancer prevention and screening recommendation statements either did not quantify benefits and harms or presented them in a way that cast a more favourable light on the potential benefits and minimized the potential harms. This is not a good situation because people generally rely on their doctor to assist them in deciding whether to participate in screening programs. If the information that the doctor is using to inform themselves and then their patients is incomplete or biased, then the patient will have incomplete information when they are making their decision.

Hopefully this situation will improve in the future as it is now recommended that guideline developers present absolute effects for important benefits and harms within a standard "summary of findings" table. If all new guidelines use this system, then it will be much easier for readers to assess and compare risks and benefits and thus better inform their patients.

Further reading:
Presentation of Benefits and Harms in US Cancer Screening and Prevention Guidelines: Systematic Review. Tanner J. Caverly; Rodney A. Hayward; Elyse Reamer; Brian J. Zikmund-Fisher; Daniel Connochie; Michele Heisler; Angela Fagerlin. J Natl Cancer Inst. 2016;108(6)

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