Detection of small nodules in lung cancer patients has no impact on patient
survival, according to a study at Duke University.
The researchers found no statistical relationship between tumor size at time
of discovery and survival. By the time a lesion has grown to 5 mm, or close
to the detectable range of a CT scan, the cancer may already have metastasized.
In other words, detecting small nodules does not necessarily increase a patient's
chance of surviving lung cancer.
The finding could have important implications for the debate about low-dose
lung cancer screening, a growing practice in many parts of the country. An underlying
assumption about screening is that early detection improves chances of survival.
The Duke findings, however, suggest that tumor size is unrelated to malignancy,
so spotting small tumors may have no value.
"We have demonstrated that lung cancer is a complex disease of the genes,
and that simply relying on size alone may not have an impact on outcome," said
Dr. Edward Patz, a professor of radiology at Duke and principal investigator
in the study.
Patz cautions against the routine use of screening for lung cancer until data
from screening studies show a reduction in lung cancer mortality.
"Low-dose CT screening for small nodules is problematic, as size may not be
an adequate prognostic indicator in patients with lung cancer," Patz said. "Just
because we can detect lesions that are small in size by CT does not mean we
will see a reduction in lung cancer mortality, which is the ultimate goal of
a diagnostic screening test."
The Duke investigators studied 285 men and 225 women diagnosed with stage
IA non-small cell lung cancer from 1981 to 1999. All the patients' tumors were
less than 3 cm at the time of detection. According to the researchers, preliminary
CT scans showed that up to 30% of the small primary lung cancers had metastasized
to regional lymph nodes or distant sites upon initial examination.
The findings of the study were published in this month's issue of CHEST.
"The unexpected observations on survival in stage IA lung cancer are timely
and provocative," said Dr. William C. Black, in an editorial in CHEST. Black
is an associate professor of radiology at the Dartmouth Medical School.
"Although these findings can probably be explained by some combination of
chance and confounding, nevertheless the study forces us to think hard about
screening with CT and reminds us that survival statistics can be misleading,"
Black said. "As the authors caution, we should not rush headlong into screening
before its effectiveness has been demonstrated by randomized clinical trials
or mathematical models that properly account for lead time, overdiagnosis, and
variations in tumor biology."
A trial to determine whether screening in fact reduces lung cancer mortality
is under consideration by American College of Radiology Imaging Network (ACRIN),
said Dr. Denise Aberle, chief of thoracic imaging at UCLA and principal investigator
of another ACRIN lung cancer screening trial.
"The disparity between survival and mortality is the single most compelling
argument for why we need to complete a multicenter randomized controlled trial
in which subjects are randomized to CT screening or no CT screening," Aberle
said. "We do know that early lung cancer detection will improve survival from
the time of diagnosis. Unfortunately, survival can increase independent of mortality.
"
— by Monika Dhingra
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