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Screening for cancer with CT scans risky

High amount of radiation, false positives

By: W. Gifford-Jones MD / The Doctor Game

Posted: 04/21/2011 1:00 AM | Comments: 0

The facts are depressing. Lung cancer kills more people than prostate, breast and colon cancer combined. Only 15 per cent of those diagnosed with lung cancer are alive in five years. Now, a study by the National Cancer Institute shows CT scans can decrease the number of deaths from this deadly disease. But what is the medical and economic cost?

Every year 24,000 new cases of lung cancer will be diagnosed in Canada and 157,000 people will die from it in the United States.

Patients with lung cancer complain of shortness of breath, frequent coughing, weight loss or coughing up blood. But too often an X-ray reveals an advanced cancer.

For years, doctors have been searching for a better diagnostic tool.

In 2002, the National Lung Screening Study enrolled 53,000 current and previous smokers ages 55 to 74 who had smoked a pack or more of cigarettes a day for the last 30 years. Half this group received a CT scan annually; the other half received the standard chest X-ray. Researchers kept tabs on them all for the next eight years.

Headlines that claim CT scans decrease lung cancer deaths by 20 per cent are once again misleading the public. It looks like an impressive figure. But putting these figures in another context, 442 smokers using standard chest X-rays died during the study. Using the CT scan 354 succumbed during the same time. A difference, but not a huge one, as some researchers contend.

What the public doesn't see is another headline: " 300 CT scans needed to save one life." Of course, many will argue that you cannot put a price on one life. But money is not the only factor if someone suggests a CT scan.

The greater the exposure to radiation, the greater the risk of developing a malignancy. One CT scan is the same as saying OK to 500 standard chest X-rays. Those in the study who were monitored for eight years by an annual CT scan received the equivalent of 4,000 chest X-rays. So there's a radiation price to pay for earlier diagnosis and a reason there are pros and cons to CT scans.

Another factor is passed over too lightly. The study revealed that 25 per cent of those in the study required follow-up tests. Why?

Because the CT scan is much like a microscope. The greater the power of the microscope, the more detail that can be detected. That's the good news. The bad news is that CT scans see so much more detail than a standard chest X-ray that it's sometimes impossible to know if the mass is a cancer or some other problem such as scar tissue. This is called a "false positive test."

This creates a dilemma. If the small mass is due to malignancy, doing nothing further can result in a lethal outcome. The only recourse is to either remove the lesion or take a biopsy of the mass. But this means entering the chest cavity, not exactly a minor procedure. Fortunately, the end result is usually good news, but it results in a large number of patients having a surgical procedure they did not need.

What will be the outcome? Give doctors new, expensive techniques and they will use them. So I predict this study will open the floodgate to a huge number of CT scans and this will result in too many complications from false-positive tests and have only a modest effect on saving lives.

The cost of this study was $250 million and good sense could have predicted much of the outcome. One could argue that these funds could have been better spent trying to educate young people to never start smoking.

See the website www.docgiff.com For comments info@docgiff.com

Republished from the Winnipeg Free Press print edition April 21, 2011 A23

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