S & T
April 25, 2012
Lung cancer: CT screening only for heavy smokers
The Hindu CAUTION ADVISED: Low-dose CT
screening produces large false-positive results. Photo: K.R. Deepak
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
percent 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 all
reputable sources. Do not trust advertisements glorifying CT
screening.
K.S. PARTHASARATHY , Former Secretary, Atomic Energy
Regulatory Board
(ksparth@yahoo.co.uk)
Keywords: computed
tomography, lung cancer
screening
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