How to think about cancer screening tests

I wrote the other day of a new recommendation that men not undergo the PSA test for prostate cancer. It's still a choice, and some men, and doctors, might want the test. National statistics are not the same as your particular body.

The decision to screen for breast cancer is somewhat similar -- there are questions about whether it actually saves lives.

Dr. H. Gilbert Welch, a professor of medicine at the Dartmouth Institute for Health Policy and Clinical Practice, has written an excellent article for The New York Times explaining the difficulty of deciding, and I recommend that you read all of it.

I'll just grab a few of the highlights.

Both breast and prostate cancer screening are really difficult calls, and the statistical differences between them are only of degrees. Reasonable individuals, in the same situation, could make different decisions based on their valuation of the benefits and harms of screening.

Screening is like gambling: there are winners and there are losers. And while the few winners win big, there are a lot more losers.

False positives are really common in both breast and prostate cancer screening. Approximately 15 to 20 percent of women and men who are screened annually over a 10-year period will have to undergo at least one biopsy because of a false-positive mammogram or PSA — prostate-specific antigen — test.

Patients who are overdiagnosed are the big losers here. They undergo surgery, radiation and chemotherapy unnecessarily. And then there are the associated complications: chemotherapy can cause nausea and radiation can burn normal tissue; breast surgery can be disfiguring, and prostate surgery can lead to bladder and sexual dysfunction.

Now let’s consider the winners — those who have avoided dying from breast or prostate cancer by getting screened. While there is some debate about whether they really exist, my reading of the data is that they do, but they are few and far between — on the order of less than 1 breast or prostate cancer death averted per 1,000 people screened over 10 years. That’s less than 0.1 percent.

"The truth is that neither test works that well," he concludes. "Even with screening, most people destined to develop deadly, untreatable cancers will still do so. When it comes to breast and prostate cancer screening, there are no right answers, just trade-offs."

It's worth your time to read the whole thing.