Low dose CT screening for lung cancer is recommended only for 55-74-year-olds who have smoked a pack daily for 30 years

On April 23, 2012, the American Lung Association (ALA) released its interim guidance recommending low dose computed tomography (CT) screening for diagnosing lung cancer among smokers. The recommendation is based on the first report of the ALA lung cancer screening committee, chaired by Dr. Jonathen Samet from the University of Southern California.

The recommendation

ALA recommends screening only for a limited group. These are current or former smokers, aged 55 to 74 years with a smoking history of at least 30 pack-years and no history of lung cancer.

Smoking history of 30 pack years means smoking a pack of cigarettes daily for thirty years or two packs daily for 15 years etc.

ALA notes that while CT screening for lung cancer may save lives, it should not be recommended for everyone due to many known and unknown risks that may be associated with the screening and subsequent medical evaluation and follow-up. Radiation risk is one of them.

In spite of this caution, Auntminnie.com, a trade journal, stated that the move is a major step toward the development of a population-based CT screening programme in the U.S.

The U.S. National Cancer Institute's National Lung Screening Trial (NLST), found that low-dose CT can reduce mortality by at least 20 per ecnt compared to chest x-ray, and other reports have pushed the estimated mortality gains even higher. The ALA guidelines followed the results of NLST of smokers at-risk, released in November 2010.

Even in this high risk group, 320 persons had to be screened with CT to prevent one lung cancer death.

The benefit of CT screening for lung cancer cannot be easily estimated for populations with risk profiles that are different from those of the NLST participants.

Can cause cancer

According to Centers for Disease Control and Prevention, screening with CT scans is not risk-free. Radiation exposure from repeated CT scans is cumulative and can lead to cancer.

Average effective radiation dose in “low dose” CT in NLST was 1.5 mSv as against 7 mSv in a full diagnostic helical CT.

Specialists have criticised low-dose CT screening due to the large number (as high as 25 per cent) of false-positive results, meaning that the positive finding did not prove to be lung cancer following diagnostic investigations. People who receive false-positive results may be subjected to unnecessary testing, including more radiation exposure, invasive diagnostic and surgical procedures, complications, and even death, diminishing the benefit of early cancer detection.

Over-diagnosis due to screening must have revealed indolent cancers which may never progress into full blown cancer. They may end up undergoing an invasive intervention that they would not otherwise need.

According to ALA, individuals should not receive a chest X-ray for lung cancer screening as it has low sensitivity.

ALA Committee suggested that ALA should ask hospitals and screening centres to: establish ethical policies for advertising and promoting lung cancer CT screening services; develop educational materials to assist patients in having careful and thoughtful discussions between patients and their physicians regarding lung cancer screening and to provide lung cancer screening services with access to multidisciplinary teams that can deliver the needed follow-up for evaluation of nodules.

Smoking, major cause

Lung cancer is a fatal disease. Currently, specialists believe that smoking causes up to 80-90 per cent of lung cancer cases.

The significance of the guidance is evident as the five-year survival rate for lung cancer presently stands at 15.6 percent as compared to an over 90 percent survival rate for breast, colon and prostate cancers.

ALA recommendation may lead to many undesirable developments. Hospitals may start direct-to-consumer advertising to recruit patients who might have resources to pay out-of pocket for low-dose CT screening.. “…the promotion of such services should not prey upon the public's fear of lung cancer while leading them to believe that low-dose CT screening will eliminate all risk from lung cancer,” ALA warned.

“Unfortunately, even before the NLST results were released, CT screening for lung cancer was being offered by some institutions and subsequent to the release an increasing number of well-respected medical centres throughout the country are offering lung cancer screening to their constituents at markedly reduced prices.” ALA observed.

Public cautioned

“Never starting smoking and quitting smoking still remains the best way to prevent lung cancer”, Dr Norman H. Edelman, Chief Medical Officer, American Lung Association cautioned the public.

Individuals have to take their own decisions on screening based on inputs from allreputable sources. Do not trust advertisements glorifying CT screening.

K.S. PARTHASARATHY

Former Secretary, Atomic Energy Regulatory Board

(ksparth@yahoo.co.uk)

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