|Chest X-Rays Can Detect Early Lung Cancer But Also Can Produce
Many False-Positive Results
A new study from the National Cancer Institute (NCI), part of the National
Institutes of Health, shows that screening for lung cancer with chest X-rays
can detect early lung cancer but also can produce many false-positive test
results, causing needless extra tests. This report, which summarizes preliminary
results from the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening
Trial, appears in the December 21, 2005, Journal of the National Cancer Institute.*
About 170,000 people in the United States are diagnosed with lung cancer each
year. Most are diagnosed when their disease is advanced, and nearly 90 percent
die within two years. But catching lung cancer early — when surgery is a treatment
option — improves survival substantially, and 70 percent of patients who are
diagnosed early may survive at least five years.
Between 1993 and 2001, PLCO investigators enrolled 154,942 men and women who
were 55 to 74 years of age. These participants included current and former smokers,
as well as individuals who never smoked. These findings, the first published
lung cancer screening results from the PLCO, are based on an analysis of the
trial participants’ initial chest X-rays. It is the first large, controlled study
to evaluate screening for lung cancer in women, whose smoking rates have increased
in recent years.
“There is no accepted early screening technique for lung cancer,” said Christine
Berg, M.D., the NCI investigator who leads the PLCO trial. “The PLCO trial will
show if chest X-rays, by catching lung cancer when it is still operable, can
reduce the death rate from lung cancer.”
Of the 67,038 men and women who received a baseline chest X-ray upon entering
the trial, 5,991 (8.9 percent) had abnormal results that required follow-up.
After undergoing additional tests, 126 (2.1 percent of the 5,991 participants
with abnormal X-rays) were diagnosed with lung cancer within 12 months of the
initial chest X-ray.
“The positive predictive value was low,” said Berg. “That means there were a
lot of false positives on the initial X-rays. If you get a positive result from
a chest X-ray, the message is ‘don't panic.’” Berg also noted that tissue variations
and other benign factors can resemble tumors on an X-ray.
Of the cancers detected, though, 44 percent were stage I, meaning those patients
were good candidates for surgery. “The rate of early cancer detection was better
than what we see in the general community,” said Berg. “But it remains to be
seen if that translates into a mortality benefit. It is too early to make any
recommendations regarding chest X-rays as a lung cancer screening tool in the
Chest X-rays have not been shown to reduce the death rate from lung cancer,
according to several previous studies. Because of their smaller enrollments,
however, these earlier studies may have overlooked a small but important benefit
of annual chest X-rays. One of the long-term goals of the PLCO trial is to determine
whether chest X-rays can reduce lung cancer mortality in men and women 55 to
74 years of age.
Participants in the intervention group of this study — those who received
an initial (baseline) chest X-ray to screen for lung cancer — are being tracked
alongside participants in the control group — a group of equal size that did
not receive screening chest X-rays. Future analysis will reveal if the intervention
group has a lower lung cancer mortality rate than the control group.
The current analysis confirmed that smoking vastly increases the risk for lung
cancer. Of current smokers in the trial, 6.3 people per 1,000 screened were diagnosed
with lung cancer. For former smokers (those who quit for less than 15 years),
the lung cancer detection rate was 4.9 per 1,000. Among non-smokers, lung cancer
was diagnosed in 0.4 individuals per 1,000 screened. Lung cancer rates were similar
for men and women smokers, but, for unknown reasons, men had more positive X-rays
(9.6 percent) than women (8.2 percent).
“The take-home message is to never start smoking, and if you do smoke, to quit,” said
Another NCI-supported study, the National Lung Screening Trial (NLST), is comparing
two ways of detecting lung cancer: spiral computed tomography (CT) and standard
chest X-ray. Both chest X-rays and spiral CT scans have been used to find lung
cancer early. So far, neither chest X-rays nor spiral CT scans have been shown
to reduce a person's chance of dying from lung cancer. This study will aim to
show if either test is better at reducing deaths from this disease.
For more information about cancer, please visit the NCI Web site at http://www.cancer.gov or call NCI's Cancer Information Service at 1-800-4 CANCER (1-800-422-6237).
For more information on the PLCO, go to http://www3.cancer.gov/prevention/plco/index.html.
For more information on NLST, go to http://www.cancer.gov/nlst.
For more information on quitting smoking, go to http://www.cancer.gov/cancertopics/tobacco/quitting-and-prevention.
The National Institutes of Health (NIH) — The Nation's Medical Research
Agency — includes 27 Institutes and Centers and is a component of
the U. S. Department of Health and Human Services. It is the primary Federal
agency for conducting and supporting basic, clinical, and translational medical
research, and it investigates the causes, treatments, and cures for both common
and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov.