A scan is helping doctors to identify lung cancer earlier but it may cause needless anxiety for some, a cancer prevention specialist says.

An international clinical trial aims to determine whether giving regular CT scans to smokers and ex-smokers picks up lung cancer tumours earlier, when the disease may be more curable.

Lung Cancer survivor Kathy Kernohan
Lung Cancer survivor Kathy Kernohan

It's too soon to say that screening healthy people with spiral CT scans can actually save lives because experts don't know whether small tumours in the lung will go on to become dangerous.

"We may be able to pick them up at earlier stages," said Dr. Barnett Kramer of the National Institutes of Health in Rockville, Md. "But that is not the same as actually benefiting patients. It's certainly not proof that you'll decrease their risk of dying of lung cancer."

The Toronto team has scanned 850 people so far. In 25 per cent, they've found something suspicious, but only two of the 25 actually have cancer – a high rate of false positives.

Dr. Heidi Roberts
Dr. Heidi Roberts

"Early lung cancer looks quite similar to any of these very harmless nodules," said Dr. Heidi Roberts, a radiologist at Toronto's Princess Margaret Hospital, the only Canadian site participating in the trial. "We just have to find out which one of these nodules are actually malignant."

To find out, people need to wait three months before having the scan again.

If the nodule has grown or changed, a biopsy is done. If there are no changes, they've worried for three months for nothing.

In a few cases, people may undergo a biopsy before finding out they're free of cancer.

"It's less clear whether there are benefits in terms of saving lives from lung cancer," said Kramer. "And if so, how they compare against the known harms."

For Kathy Kernohan of Toronto, who quit smoking 12 years ago, the scans picked up her lung cancer. Kernohan said she felt fortunate when she heard TV news anchor Peter Jennings died of lung cancer at the age of 67.

Jennings said he smoked about 20 years ago and resumed the habit after the attacks of Sept. 11, 2001.

"He didn't get the advance notice, he had four months," said Kernohan. "I think it is the common story with lung cancer, and I hate to think that I would've been long gone."

It may be another seven years before doctors can say conclusively that screening for lung cancer saves lives. In the meantime, their advice remains: quit smoking and do not take it up again.