Sensitive Scan Catches Lung Cancer Early
But jury's still out on whether it improves survival rate
FRIDAY, March 1, 2002 (HealthDayNews) -- A highly sensitive scanning technology can catch lung cancer early, but it's not yet clear whether it can also reduce the death rate from the disease.
Doctors at the Mayo Clinic say low-dose, spiral-computed tomography scans (spiral CTs) trounce conventional methods when it comes to finding the first signs of lung cancer. However, the technique has a disturbingly high "false positive" rate, and researchers are still searching for a solid link between spiral CT screening and fewer deaths from lung cancer.
The five-year survival rate for lung cancer is less than 15 percent, and early detection of the disease is critical.
"There really hasn't been any change in the survival [rate] of lung cancer in the last several decades," says lead investigator Dr. Stephen J. Swensen. "This offers the hope of finding lung cancer earlier, and therefore potentially saving some lives."
The findings appear in the American Journal of Respiratory and Critical Care Medicine.
In the latest study, the researchers performed a baseline screening of 1,520 people aged 50 or older, all of whom had smoked 20 "pack years" with one pack year equivalent to one year of smoking 20 cigarettes a day. All of the study participants were at high risk for lung cancer.
Each person underwent a spiral CT scan, along with sputum cytology essentially, an examination of their phlegm for cancerous cells.
The spiral CT scan identified cancer in 23 cases, while sputum cytology detected only two cases. More than half of the tumors detected by the scans were at the earliest stage of development, and 22 of the patients underwent curative surgery to remove their cancers.
However, the scans also identified 2,244 lung nodules in more than 1,000 of the smokers. Seven benign lung nodules were surgically removed, but the researchers estimate that 99 percent of the masses identified were "false positives," meaning they weren't cancerous.
In addition, the researchers also calculate a 26 percent "false negative" rate in the baseline scans, referring to abnormalities that might have been missed.
Swensen says the high rate of false positives produced by this method could end up doing more harm than good. Not only could it cause stress for people who would think they have lung cancer, it could also lead to the inconvenience and radiation of follow-up scans, and the potential for invasive surgery and any related complications, he says.
Dr. Nerinder S. Paul, divisional head of cardiothoracic imaging at the University Health Network and Mount Sinai Hospital in Toronto, says spiral CT scans "are very sensitive at picking up abnormalities."
"The problem is that not everything that you pick up is going to be a tumor, or even an early tumor. Some of it's going to be old scars or [granulomas from infections or tuberculosis]," he says. "All of these things can leave little opacities in the lungs. The technique will pick up all these opacities."
The original idea was that a spiral CT could be used to screen high-risk populations, followed by more traditional CT scans to examine abnormalities detected in the first scans. Paul says other centers could then perform biopsies of the abnormalities.
One current tactic with a positive result is to put the person on antibiotics, then repeat the spiral CT scan, says Paul. If the abnormality has disappeared, it was probably due to an infection. "If it's still there, depending on what size it is, you either repeat the CT or you do a biopsy or some sort of procedure," he says.
In a high-risk population, Paul adds, if doctors don't find any abnormalities on the first spiral CT scan, another one is repeated one year later.
However, Swensen says it's still not clear whether using spiral CT scans could ultimately improve the survival rate from lung cancer.
"Even though we're able to find lung cancers earlier, we don't know if it's early enough," he says. "It's absolutely unproven that it saves lives."
Swensen and his colleagues will continue to scan the same 1,520 participants every year, in hopes of determining whether screening to catch early lung cancers affects their risk of death.