Lung cancer CT screening leads to more false positives

A lung cancer screening technique promoted by some patient advocates leads to a false diagnosis of the disease in about 33 percent of patients after two annual tests, researchers said.

Patients who underwent computed tomography screenings, or CT scans, were more than twice as likely to have a false finding of cancer compared with patients who had standard chest X-rays, according to a study in the Annals of Internal Medicine.

CT scans, which expose patients to a low dose of radiation, have been promoted by physicians, hospitals and patients groups as a tool for detecting lung cancer early, the study authors said. Lung cancer killed an estimated 159,390 people in the U.S. in 2009, more than any other type of cancer, according to the National Cancer Institute. The disease is difficult to treat unless found at an early stage, the authors said.

"False positives can lead to invasive procedures, which in turn are unnecessary because you don't have cancer," said Jennifer Croswell, the study's lead author and a researcher at the National Institutes of Health. "As a patient, you go from thinking you're healthy and asymptomatic to where you don't know if you have cancer or not. And that can be anxiety producing."

The study of 3,190 current or former smokers found that patients who received one CT scan had a 21 percent risk of a false-positive result, compared with a 9 percent risk for those who had a chest X-ray. The risk was 33 percent for patients who underwent two annual CT scans compared with a 15 percent risk of an erroneous finding in those who had two chest X-rays, the study found.

Seven percent of those with a false result after a CT scan underwent a follow-up medical procedure, compared with 4 percent of the chest X-ray group. The most common follow-up procedure was a bronchoscopy, in which a flexible, lighted tube is inserted through the patient's throat into the lung to collect a tissue sample.

The American Cancer Society and American Lung Association don't recommend CT scans or chest X-rays as a screening tool for lung cancer in patients who may be at higher risk for the disease but have no symptoms, Croswell said.

In 2008, the Bonnie J. Addario Lung Cancer Foundation, a San Francisco-based patient advocacy group, funded a "Demand a CAT Scan" advertising campaign in Atlanta, Los Angeles, New York, San Francisco to promote awareness of the disease, according to the foundation's Web site. One of the ads carried the message "CT Scan: Think of it as a mammogram for your lungs."

While some studies have "potentially suggested" that CT scans may be helpful in detecting lung cancer, no rigorous clinical trials have demonstrated that early screenings can reduce a person's chance of dying from the disease, she said.

More data on the benefits and risks of CT scans for lung cancer is needed because the tests expose patients to low-dose radiation that itself may increase the risk of people developing cancers, Edelman said.