CT screening for lung cancer does not increase
29 March 2007
A US-Italian study of the use of computed tomography (CT) to screen
current or former smokers for lung cancer has found that screening did not
reduce deaths from lung cancer. Screening found more than three times as
many lung cancers and ten times as many surgeries were performed, but there
was no effect on survival rate.
The multi-centre study was led by researchers at Memorial Sloan-Kettering
Cancer Center. The findings appear in the March 7 issue of the Journal of
the American Medical Association.
Although CT screening found nearly three times as many lung cancers as
predicted, the researchers found that early detection and treatment did not
lead to a corresponding decrease in advanced lung cancers or a reduction in
deaths from lung cancer.
“Ours is the first study to ask whether detecting very small growths in
the lung by CT is the same as intercepting cancers before they spread and
become incurable. We found an answer and it was, ‘NO’," said Peter B. Bach,
MD, MAPP, a lung physician and epidemiologist at Memorial Sloan-Kettering
and the study’s first author. "Early detection and additional treatment did
not save lives but did subject patients to invasive and possibly unnecessary
Beginning in 1998, 3246 asymptomatic men and women with a median age of
60 who had smoked or still smoked for an average of 39 years were screened
for lung cancer with state-of-the-art multi-detector CT at either the Mayo
Clinic in Minnesota, the H. Lee Moffitt Cancer Center & Research Institute
in Florida, or the Instituto Tumori in Italy.
Each study provided an initial CT scan and then at least three subsequent
annual exams. The researchers followed the volunteers to see how many had
cancers detected by screening and how many had surgery to remove them. They
then used government death records to follow the study participants for five
years to see if they died of lung cancer. The researchers compared what they
saw to what statistical models predicted would happen without screening.
The models were developed for this purpose by Dr. Bach and Colin B. Begg,
Ph.D., Chairman of the Department of Epidemiology and Biostatistics at
Memorial Sloan-Kettering, and have been shown to be accurate in study
populations like the ones analyzed.
Over the course of the studies, screening found more than three times as
many lung cancers as the number that would have been diagnosed without
screening, and there were ten times as many surgeries performed for lung
cancer compared to what was expected. This meant that as a direct result of
the test, an additional 99 people were diagnosed with lung cancer and an
additional 98 had lung surgery. However, the early detection and treatment
did not change the death rate. There were 38 deaths due to lung cancer, and
39 would have occurred without screening.
“The purpose of large-scale screening is to save lives, but after five
years of follow-up, our data provides no evidence that CT screening
prevented deaths from lung cancer,” said Dr. Begg, the paper’s senior
author. “Our findings are consistent with the results of earlier studies of
lung cancer screening with chest x-rays, which showed no benefit to this
type of screening for current and former smokers.”
CT screening is not without risk. The radiation can become significant
when the scans are repeated every year. Because the test is not very
specific, it is known to have false positive results, which can lead to
additional CT scans at full radiation doses and invasive procedures like
lung biopsies. This study also suggests CT screening can lead to additional
major surgeries to remove very small growths that look like lung cancer but
do not pose a meaningful threat to the patient’s health.
“With lung cancer the number one cause of cancer deaths in the United
States, the medical profession continues to seek an effective and safe
approach to prevent deaths from this disease. According to our study, CT
screening may not be it,” said Dr. Bach.