NEW YORK, July 18 (Reuters Life!) - CT scans to measure lung
tumors can be unreliable, potentially leading patients and
doctors to believe cancer is growing when it's not, according to
In principle, that could mean stopping a treatment that is
actually keeping the tumor in check, researchers said in the
study, which they said was the first to test how reliable lung
cancer scans are, and appeared in the Journal of Clinical
"The patient and the doctor both need to understand that
small changes don't necessarily mean much," said Gregory Riely,
at Memorial Sloan-Kettering Cancer Center in New York.
"Changes of up to 10 percent can happen simply as a result
of the inherent variability of CT imaging."
For the study, the Sloan-Kettering team asked patients with
late-stage lung cancer if they'd be willing to have two chest CT
scans within minutes. Thirty-three patients said yes.
Doctors normally scan such patients every few months to see
if their tumor is growing, which could be a signal to change
Then the researchers gave the images to three radiologists
who had no idea the scans had been repeated before the tumors
could have grown or shrunk appreciably.
But the radiologists reported many changes, ranging from a
23 percent shrinkage to a 31 percent growth.
Overall, three percent of the tumors appeared to have grown
so much that doctors would diagnose disease progression
according to common criteria. And the smaller the tumor, the
bigger the variation.
Riely said some doctors will make treatment decisions based
on tiny changes seen on scans, although that might be a costly
mistake, according to the study's findings.
"We begin to put more and more stock in the data without
really understanding the true variability of those
measurements," he said.
"The changes are not clinically meaningful and we should not
alter clinical care based on them."
Riely did say, though, that the findings did not mean that
patients should get repeat scans, which would increase their
Most likely, the results also apply outside of lung cancer,
although patients' breathing could make the chest scans
Michael Maitland, at the University of Chicago and who wrote
an editorial accompanying the study, said it was surprising such
a study had not been done up to now and it was likely to be
"This is telling us scientifically how much noise is
naturally there without any treatment or the cancer getting
worse," he told Reuters Health.
"It's an important thing to do whenever you are going to use
any kind of marker for a disease.
He added that the findings will be helpful to drug
developers, who look at increasingly small changes in tumor size
during drug testing, forgetting that the scans might be
unreliable at that scale.
In addition, the new data can help scientists build better
models of cancer progression that might save both time and
energy in clinical trials.
"There is a real opportunity here to update our systems and
take advantage of the new technology," Maitland said.
(Reporting by Frederik Joelving at Reuters Health; editing by