John M Mandrola, MD
|January 12, 2016
An unpleasant emotion caused by the belief that something is dangerous. This is fear. This is cancer.
The motivation to screen for cancer, therefore, is easy to understand.
The problem: cancer screening has not worked. Recent reviews of the evidence show that current-day screening techniques do not save lives. Worse, in many cases, these good-intentioned searches bring harm to previously healthy people.
I realize this sounds shocking. It did to me, too. Millions of women and men have had their breasts squished, veins poked, lungs irradiated, and bowels invaded in the name of “health” maintenance. I’ve been scolded for forgoing PSA tests and colonoscopy — “you should know better, John.”
I know what you may be thinking. We have all heard the anecdotes — cases that are often celebrated in local news reports and hospital marketing material. People saved by early detection, and the opposite: the unscreened felled by late-stage disease.
Anecdotes, however compelling, are not evidence. When you pull up a chair, open your computer, take a breath, suspend past beliefs, and look for the evidence that screening saves lives, it simply isn’t there.
One reason that this many people (doctors and patients alike) have been misled about screening has been our collective attachment to the belief that if screening lowers disease-specific death rates, that would translate to lower overall mortality. That is: breast, lung, and colon cancer are bad diseases, so it makes sense that lowering death from those three types of cancer would extend life.
It is not so.
Facts, Not Fear
In a comprehensive review of the literature
published in the BMJ
, Drs Vinay Prasad (Oregon Health Sciences University, Portland) and David Newman (School of Medicine at Mount Sinai, New York), along with journalist Jeanne Lenzer, find that disease-specific mortality is a lousy surrogate for overall mortality. They report that when a screening technique does lower disease-specific death rates, which is both uncommon and of modest degree, there are no differences in overall mortality.
The authors cite three reasons why cancer screening might not reduce overall mortality:
Screening trials were underpowered to detect differences. I’m no statistician, but doesn’t the fact that a trial requires millions of subjects to show a difference, mean there is little, if any, difference?
“Downstream effects of screening may negate any disease-specific gains.” My translation: harm. Dr Peter Gøtzsche (Nordic Cochrane Center, Copenhagen) wrote in a commentary that “screening always causes harm. Sometimes it also leads to benefits, and sometimes these benefits outweigh the harms.” To understand harm resulting from screening, one need only to consider that a prostate biopsy entails sticking a needle through the rectum, or that some drugs used to treat breast cancer damage the heart.
Screening might not reduce overall mortality because of “off-target deaths.” An illustration of this point is provided by a cohort studythat found a possible increased risk of suicide and cardiovascular death in men in the year after being diagnosed with prostate cancer. People die — of all sorts of causes, not just cancer.
Let’s also be clear that this one paper is not an outlier. A group of Stanford researchers performed a systematic review and meta-analyses of randomized trials of screening tests for 19 diseases (39 tests) where mortality is a common outcome. They found reductions in disease-specific mortality were uncommon and reductions in overall mortality were rare or nonexistent.
Drs Archie Bleyer and H Gilbert Welch (St Charles Health System, Central Oregon, Portland) reviewed Surveillance, Epidemiology, and End Results (SEER) data from 1976 through 2008 and concluded that “screening mammography has only marginally reduced the rate at which women present with advanced cancer and that overdiagnosis may account for nearly a third of all new breast cancer cases.”Likewise, a Cochrane Database Systematic review of eight trials and 600,000 women did not find an effect of screening on either breast cancer mortality or all-cause mortality. This evidence caused the Swiss medical board to abolish screening mammography.
These are the data. It’s now clear to me that mass cancer screening does not save lives. But I’m still trying to understand how this practice became entrenched as public-health gospel. It has to be more than fear.
How We Say It Matters
Dr Gerd Gigerenzer (Max Planck Institute, Berlin, Germany) offered a clue in his editorial accompanying the recently published literature review and analysis by Prasad and colleagues. He pointed to language and the ability of words to persuade. Instead of saying “early detection,” advocates might use the term “prevention.” This, Dr Gigerenzer says, wrongly suggests screening reduces the odds of getting cancer. Doesn’t looking for cancer increase the odds of getting the diagnosis of cancer?
Gigerenzer noted two other ways language is used to emphasize screening benefits over harms:
The reporting of benefits in relative, not absolute terms.
The equating of increases in 5-year survival rates with decreases in mortality.
I would add to this list of word misuse, the practice of referring to women sent to mammography screening as patients. They are not patients; they are well people.
Dr Gigerenzer agreed with the commonsense notion that overall mortality should be reported along with cancer-specific mortality. His editorial included a fact box
on breast cancer early detection using mammography provided by the Harding Center for Risk Literacy. I challenge you to tell me why such text boxes should not be shown to people before they undergo screening,
Fixing a Public-Health Problem
Given these revelations, I conclude that we have a massive public-health problem. Any expert in problem solving will tell you the first step of getting out of hole is to stop digging. I see three obvious next steps:
The first action healthcare experts should take is to spread the word that there is nothing about the mass screening of healthy people for cancer that equates to health maintenance. Embrace clear language. Saying or implying that screening saves lives when there are no data to support it and lots to refute it undermines trust in the medical profession.
The second action healthcare experts should take is to stop wasting money on screening. If the evidence shows no difference in overall mortality, why pay for it? I’m not naive to the fact that use of clear language will decrease the number of billable procedures. I am not saying this will be easy. One first move that would be less painful would be to get rid of quality measures or incentives that promote screening.
I want to be clear; I’m not saying all cancer screening is worthless. People at higher baseline risk for cancer, such as those with a family history of cancer or environmental exposures, might derive more benefit than harm from screening. Prasad, Lenzer, and Newman say this group of patients would be a good place to spend future research dollars. That sounds reasonable. I also acknowledge that some people, even when presented with the evidence, will want to proceed with screening. We can argue about who should pay for non–evidence-based medical procedures.
The most important action that all of us (patients, nurses, doctors, and healthcare writers) should take is to learn from this revelation. There’s nothing bad about the fact that current-day screening tests don’t save lives. Cancer is a tough disease, and in some ways, it may be the natural order of cell biology. What’s bad about this medical reversal has been our blindness to the evidence.
We let what we believe become what we know. In clinical medicine, that should be a never event.
Prasad V, Lenzer J, Newman DH. Why cancer screening has never been shown to “save lives”—and what we can do about it. BMJ
. 2016;352:h6080. Article
Gøtzsche PC. Commentary: Screening: a seductive paradigm that has generally failed us. Int J Epidemiol.
Fang F, Keating NL, Mucci LA, et al. Immediate risk of suicide and cardiovascular death after a prostate cancer diagnosis: cohort study in the United States. J Natl Cancer Inst
. 2010;102:307-314. Article
Saquib N, Saquib J, Ioannidis JP. Does screening for disease save lives in asymptomatic adults? Systematic review of meta-analyses and randomized trials. Int J Epidemiol
. 2015;44:264-277. Abstract
Bleyer A, Welch HG. Effect of three decades of screening mammography on breast-cancer incidence. N Engl J Med
. 2012;367:1998-2005. Article
Gøtzsche PC, Jørgensen KJ. Screening for breast cancer with mammography. Cochrane Database Syst Rev
. 2013;6:CD001877. Abstract
Biller-Andorno N, Jüni P. Abolishing mammography screening programs? A view from the Swiss Medical Board. N Engl J Med
. 2014;370:1965-1967. Editorial
Gigerenzer G. Full disclosure about cancer screening. BMJ
. 2016;352:h6967 Editorial