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The draft guidelines issued on Monday by the U.S. Preventive Services Task Force call for annual CT screening of current and former smokers aged 55 to 80 with a history of smoking the equivalent of a pack a day for 30 years, or two packs a day for 15 years. The recommendation applies to those who have quit smoking within the past 15 years.

The panel gave the screening a "B" recommendation, meaning they are at least moderately certain that the benefits of testing outweigh the harms. Under the Affordable Care Act, insurers are required to cover preventive services with a grade of "B" or higher.

The recommendations, posted on the task force website, are intended to help prevent some of the 160,000 annual lung cancer deaths in the United States, which exceed the total number of deaths from breast, prostate and colon cancer combined. Smoking is the biggest risk factor for developing lung cancer, resulting in about 85 percent of lung cancers in the United States.

Dr. Michael LeFevre of the University of Missouri in Columbia, who served on the task force, said "getting screened for lung cancer is not an alternative to quitting smoking," but he said screening high-risk smokers can prevent as many as 20,000 deaths a year.

Laurie Fenton Ambrose of the Lung Cancer Alliance, a group that has long advocated for lung cancer screening, said if approved in final form, the guidelines would represent a "profound" and "monumental moment."

The guidelines largely fall in line with recommendations from most major groups of cancer experts, including the American Cancer Society and the American Society of Clinical Oncology.

But some doctors worry the rating might lead to overdiagnosis and overtreatment of cancers, in much the same way that widespread screening programs for breast and prostate cancers have done.

PROPOSED GUIDELINES

The proposed guidelines are based on a review of research studies published since 2004, the time of the group's last review. The evidence review was published in the Annals of Internal Medicine.

Some of the strongest evidence came from the National Lung Screening Test, the largest-ever lung cancer screening study that in 2011 found CT screening cuts deaths from lung cancer.

The federally funded trial, which studied 53,000 current or former heavy smokers, found that CT scanning cut lung cancer deaths in high-risk smokers by 20 percent compared to no screening or to chest X-rays, which often miss early-stage cancers.

Dr. Clifford Hudis, president of the American Society of Clinical Oncology, said the draft recommendations reflect the positions of several cancer groups.

"I think they are catching up to the science," said Hudis, adding, "We agree with them."

Of course, using a highly sensitive test like a CT scan to look for early signs of lung cancer will undoubtedly result in high rates of false positives. The NLST found that 320 high-risk smokers had to be screened to prevent one lung cancer death.

Because of that, and the potential risk from annual exposure to radiation from the CT scans, LeFevre stressed that the screening should only be used in the high-risk groups specified by the guidelines.

"We believe the benefits do outweigh the harms in the group we have targeted for screening. We are not sure of that for those of lower risk, either by age or smoking history," he said.

OVERDIAGNOSIS

The National Lung Screening Trial showed that for every five to six lives saved by screening, one person died as a result of post-screening procedures, such as a needle biopsy that collapsed their lung.

Dr. Peter Bach, director of Memorial Sloan-Kettering Cancer Center's Center for Health Policy and Outcomes, who has studied the impact of lung cancer screening said with the new guidelines, "overdiagnosis is guaranteed."

Bach said he hopes doctors will view the "B" rating as an indication that the recommendation was weak. "They are not telling people you have to do it," he said.

LeFevre said it is very important that doctors follow up tests with imaging first, rather than invasive procedures.

"Most of the abnormalities found on CT scan are not cancer, but they do lead to further testing. That is why it is important to limit this to the high-risk group," he said.

Dr. Kenneth Lin, an associate professor of family medicine at Georgetown University School of Medicine and formerly on the staff of the U.S. Preventive Service Task Force, said there is still not enough good data on the issue of overdiagnosis, which will make it difficult to counsel patients on whether to have the test or not.

"If a patient came to me asking for screening and if he/she didn't meet the criteria, I'd simply say 'no'," Lin said in emailed comments.

If patients did meet the criteria, Lin said he would press for more details on the patients potential risk for lung cancer and if the patient is still smoking, offer counseling about the need to stop.

"Then I'd explain the uncertainty regarding the harms and only order the test if they expressed a clear preference for it after all that," he said.

What worries LeFevre and others is that some doctors and hospitals will try to profit from screening, which costs a few hundred dollars a test.

"We hope that physicians will not use this recommendation to exaggerate the benefits of screening," he said.

The task force is expected to decide whether to make the recommendation final sometime after August 26 when the public comment period ends.

(This story has been corrected to make it clear that the guidelines were posted on task force website)

(Reporting by Julie Steenhuysen)