The study, based on data from the largest clinical trial of lung-cancer computed tomography (CT) screening ever conducted, represents the first time tumor size and lung cancer stage have been linked in an asymptomatic population.

Risk Persists 20-30 Years After Quitting Smoking

"The smaller the lung cancer is at diagnosis, the more likely it is to be stage 1 and curable," said lead author Dr. Claudia Henschke, principal investigator of the International Early Lung Cancer Action Project (I-ELCAP). "If small lung cancers are found, they may have a significantly improved chance of a cure." Dr. Henschke is also chief of the chest imaging division at NewYork-Presbyterian/Weill Cornell and professor of radiology at Weill Cornell Medical College.

Smokers should consider CT screening because they are at high risk of lung cancer, she advises. Former smokers remain at high risk for lung cancer for 20 or 30 years after they quit smoking and should consider annual CT screening.

"CT screening has the potential to save lives in both of these groups," she continues. "This new information should be most helpful in providing for an informed decision-making discussion between patients seeking CT screening for lung cancer and their physicians."

Small Lesions, Curable Cancer

Lung cancer is the leading cause of cancer death in both men and women, killing more people than breast, prostate and colon cancers combined, according to the American Cancer Society.

Stage 1 lung cancer has been shown to have better a cure rate than any other stage. When lung cancer is detected outside of screening, typically because of symptoms, it has often spread to the lymph nodes and beyond. At this point, the opportunity for curative resection or any effective treatment is greatly diminished.

The largest study ever undertaken to determine if annual screening by CT is effective, I-ELCAP screened 30,235 men and women at 38 institutions across the globe. The study released Monday evaluated 438 lung cancers identified in I-ELCAP and studied the relationship of cancer stage to tumor diameter in asymptomatic, latent lung cancers to determine if size is an indicator of prognosis. The researchers considered tumor diameter, consistency, and presence or absence of metastases at the time of diagnosis.

"This report confirms that small-sized lesions are a good indicator of early, curable cancer," Dr. Henschke said. "Previously, concern regarding this relationship had led some to question the benefit of screening. This issue should no longer be of concern."

Remarkable Advances in CT Scanning

The current lung cancer staging criteria considers tumors smaller than 30 millimeters without evidence of spread to be in stage 1A. The study found more than 90 percent of the lesions that are smaller than 15 mm -- about the size of a dime -- are in stage 1A, and almost all of those are curable. The researchers found that 85 percent of 16 mm to 25 mm malignancies had no lymph node metastases and that 63 percent of the 26 mm to 35 mm had not metastasized.

Because screening is useful for finding small, asymptomatic cancers, the researchers did not have many lesions larger than 35 mm to study.

"Screening allows us to find smaller lung cancers than what we typically find when patients are symptomatic," said Dr. Henschke. "Clearly, the smaller the cancer the more curable it is, and stage 1 is the most hopeful. When found in later stages, the cure rate drops dramatically."

"Therefore, our findings suggest that tumor diameter serves as a prognostic indicator for curability, perhaps even for micro-metastases not detectable by our current techniques," she adds.

Since the early 1990s, there have been remarkable advances in CT scanners, so that sub-millimeter "slicing" can now be applied to the entire chest in a single breath-hold. As a result, lung cancer is being detected when it still is smaller than in cases diagnosable prior to 1986. While CT scans once yielded 30 images, current technology yields 900 images.