Does screening for disease save lives in asymptomatic adults? NO

I remember learning in medical school about what a screening test is and the factors necessary to make a 'good' screening test.

The disease in question should:
- constitute a significant public health problem, meaning that it is a common condition with significant morbidity and mortality.
- have a readily available treatment with a potential for cure that increases with early detection.
The test for the disease must:
- be capable of detecting a high proportion of disease in its preclinical state
- be safe to administer
- be reasonable in cost
- lead to demonstrated improved health outcomes
- be widely available, as must the interventions that follow a positive result 

(American Medical Association Council on Scientific Affairs. Commercialized Medical Screening (Report A-03). no longer available online, but cited on Virtual Mentor)

We have obviously lost our way!!

In medical school I was excited about ensuring every patient got ALL THE SCREENING! I never thought I'd struggle to justify a screening test. 

These days, I would be hard-pressed today to confidently name you one "good" screening test. Maybe paps? Maybe colonoscopies? I follow my jurisdiction's guidelines. I discuss the risks and benefits of screening with patients because I'm not certain that what we are doing is definitely "good."

It's hard to summarize it any more clearly than this:

Among currently available screening tests for diseases where death is a common outcome, reductions in disease-specific mortality are uncommon and reductions in all-cause mortality are very rare or non-existent.

A paper in the International Journal of Epidemiology from June 2014 that just came to my attention recently draws this conclusion.

The authors looked at data from 48 Randomized Controlled Trials (RCTs) and 9 meta-analysis on the subject of screening tests (39 of them) for 19 potentially deadly diseases. The studies they included regarded things like mammography for breast cancer, echocardiography for heart disease, PSAs for prostate cancer, and so on.

Some limitations are acknowledged but I also wonder if there is another. For very worthwhile "common sense" things (if these things exist, and I'm not saying they do!) there is little published data. For example, the efficacy of the newborn screening exam or GBS screening in pregnancy don't seem to have been thoroughly studied but are considered to be "law, written in stone" in practice. For the more controversial screening tests, there are more trials published, and so that might weight this meta-analysis towards saying that screening tests on the whole are not useful. I actually think the conclusion the their analysis is appropriate, as the closer we look at other "written in stone" practices, the more we realize we were wrong!

This sentence in the discussion of the article I think sums up the complex nature of the results really well:

There are many potential underlying reasons for the overall poor performance of screening in reducing mortality: the screening test may lack sufficient sensitivity and specificity to capture the disease early in its process; there are no markedly effective treatment options for the disease; treatments are available but the risk-benefit ratio of the whole screening and treatment process is unfavourable; or competing causes of death do not allow us to see a net benefit. Often, these reasons may coexist. Whether screening saves lives can only be reliably proven with RCTs.

See for yourself! Read the full article.

 

How can you have an overdiagnosis of cancer? Either it's there, or it's not.

"How can you have an overdiagnosis of #cancer?  Either it's there, or it's not." – @susila55

[click to expand]

Rates of new diagnosis and death for five types of cancer in the US, 1975-2005. Adapted from Welch and Black, in Preventing overdiagnosis: how to stop harming the healthy. BMJ 2012; 344:e3502

In response to tweets about a potential for overdiagnosis in thyroid cancer cases, a twitter user, Susan Burke Mangano (@susila55), asked this question.

There have been many articles lately on overdiagnosis of almost all kinds of cancer. Our twitter discussion was mainly around thyroid cancer (with Dr Gilbert Welch leading in publications eg. Current Thyroid Cancer Trends in the United States).

Whether breast or prostate, thyroid or renal, the conclusions are generally the same: we are diagnosing more and more cancer, but it is not affecting mortality rates.

How? What?

"There is an ongoing epidemic of thyroid cancer in the United States. The epidemiology of the increased incidence, however, suggests that it is not an epidemic of disease but rather an epidemic of diagnosis." – Welch et al.

I'm not going to explain it here myself since it has already been done well in many places, the most straightforward of which is this video/article combo, by the Wall Street Journal.

I highly recommend you take a look.

Read Some Cancer Experts See 'Overdiagnosis,' Question Emphasis on Early Detection in the Wall Street Journal.

 

* As they have just locked this article (you need a WSJ subscription or institutional access eg. university library account), I will include a few pertinent quotes here:

 

While it's clear that early-stage cancers are more treatable than late-stage ones, some leading cancer experts say that zealous screening and advanced diagnostic tools are finding ever-smaller abnormalities in prostate, breast, thyroid and other tissues. Many are being labeled cancer or precancer and treated aggressively, even though they may never have caused harm . . .
"We're not finding enough of the really lethal cancers, and we're finding too many of the slow-moving ones that probably don't need to be found," says Laura Esserman, a breast-cancer surgeon at the University of California, San Francisco. . . .
"Unfortunately, when patients hear the word cancer, most assume they have a disease that will progress, metastasize and cause death," the group wrote in the journal Lancet Oncology in May. "Many physicians think so as well, and act or advise their patients accordingly." . . .
Overdiagnosis--the detection of tumors that aren't likely to cause harm--is now a hot topic in other cancers as well. A growing volume of studies estimate that as many as 30% of invasive breast cancers, 18% of lung cancers and 90% of papillary thyroid cancers may not pose a lethal threat. . . .
"Everyone says they'd be willing to be overtreated if it means not dying--but that's a big fallacy," says Dr. Esserman. "By treating 1,000 people who have low-risk disease, we're not going to save the one person with aggressive disease." . . .
Says Dr. Esserman: "We need to start testing some of these ideas, rather than just fighting over them. People are afraid to do less. We want to figure out how to do less safely."
- Melinda Beck, WSJ