That’s something many of us may not ask ourselves when our doctor suggests a test to look for evidence of a disease when no symptoms are present.
But I would argue that you absolutely should, if your doctor doesn’t go over how likely you are to benefit from a screening test versus the type and magnitude of potential harm.
That is what informed consent is all about. And research suggests that when we don’t have that information, the vast majority of us wildly overestimate the potential benefit
Take fecal occult blood testing for colorectal cancer. When 1,000 people are screened for 10 years, this test prevents 1 to 2 deaths. Yet in a study that asked 977 adults how many lives they expected the test to save per 1,000 people over that period, 94% gave a higher number. The highest proportion — a third of these individuals — answered 336.
Similarly, even if we’re aware that these tests have potential downsides, we may very well not be aware of how those numbers measure up to the benefits.
For instance, according to a Canadian group that weighs the evidence behind common screening tests, among women at average risk aged 50 to 69, those who undergo regular screening mammograms have a 1 in 196 chance of dying from breast cancer (that’s 0.65%) versus 1 in 155 (or 0.46%) among those who skip screening.
(There is dispute in the medical community over these numbers: many radiologists argue that recent research suggests greater benefit, while some experts with differing backgrounds argue when you add up deaths from any cause, the risk in both groups is the same. This could be due to an increase in deaths from heart disease caused by cancer treatment. You can find a more detailed explanation by reading a few of the stories I’ve listed under ‘resources’ below. The piece by Christie Ashwanden is particularly good.)
The cost? A one in four chance of having a false positive requiring further testing; a one in 28 chance of biopsy; and a 1 in 200 chance of having all or part of a breast removed unnecessarily.
I’m not here to talk you out of screening. But only you can decide how those numbers add up for you — and you can’t do that if you don’t have them in the first place.
Thank-you to the interviewees who so kindly contributed their time and expertise:
- Dr. Cornelia Baines, a professor emerita in the University of Toronto’s Dalla Lana Faculty of Public Health, division of epidemiology.
- Dr. Neil Bell, a family physician and professor in the department of family medicine within the Faculty of Medicine at the University of Alberta in Edmonton, and former member of the Canadian Task Force on Preventive Health Care’s prostate cancer screening working group.
- Dr. Scott McKay, an associate professor in the Schulich School of Medicine and Dentistry’s department of family medicine at Western University in London, Ont.
- Dr. Christopher Patterson, a geriatrician and professor emeritus in the division of geriatric medicine, within the department of medicine (Faculty of Health Sciences) at McMaster University in Hamilton, Ont.; member of the McMaster Institute for Research on Aging (MIRA), and co-investigator with the Canadian Longitudinal Study on Aging.
- Dr. Ross Upshur, head of the division of public health, in the University of Toronto’s Dalla Lana School of Public Health, and assistant director of Sinai Health Systems’ Lunenfeld Tanenbaum Research Institute.
- Breast Cancer Action (Decision Aid Brochure)
- Canadian Task Force on Preventive Health Care (Decision Aids)
- Cochrane Collaboration (Plain Language Summary of Review)
- Cochrane Collaboration (Decision Aid)
- Healthy Debate (articles including “The Mammography Controversy”
- “Science Won’t Settle the Mammogram Debate” by Christie Ashwanden
- A public talk by Dr. Michael Baum, one of the docs who led the one of the UK’s first screening mammography programs.