Early Detection of Lung Cancer--Caution Advised

Last month, when a new study showed that CAT scans could detect early lung cancer in smokers and former smokers, some research centers were flooded with phone calls from people who wanted to be tested, according to The New York Times. But, a closer look at the study results would indicate a need for caution. While the study did find a major increase in survival, it did not prove that early detection of lung cancer actually saves lives. What's more, many hospitals may have the appropriate high-tech scanning equipment but few have the personnel skilled enough to make an accurate interpretation of the results. The possibility of unnecessary surgery looms large.

At present, most lung cancer is found at a late stage, and five years after diagnosis only about 15% have survived the disease. Screening symptomless people has not been advised for about 20 years, due to the limitations of the standard chest x-ray. The new study found that the CAT scan could increase the lung cancer survival rate to 80%. It involved 1,000 male and female smokers and former smokers, who were over age 60 years and symptom-free (The Lancet, 7/10/99). All had smoked at least a pack a day for ten years or two packs a day for five years. They were given a chest x-ray and a low-dose CAT scan, which is also known as low-radiation-dose computed tomography. The study, led by Claudia I. Henschke, MD, took place at New York University Medical Center and McGill University, Montreal.

CAT scans proved to be far more efficient than chest x-rays in finding the small nodules in the lung that might become cancerous. The operative word is the previous sentence is might. Not all nodules in the lung are early manifestations of lung cancer. Yet people might be mistakenly given major surgery for a nodule that would never become malignant. Sound familiar? This is the same problem that surrounds the use of the PSA screening test for early prostate cancer and mammography screening for non-palpable breast abnormalities (e.g., ductal carcinoma in situ).

Though false-alarms were common in the New York/Montreal study, the researchers were not quick to send people off for major surgery. In fact, no study participant had a lung removed for a benign nodes. Nodules were detected in 233 study participants given initial CAT scan, compared with 68 discovered on chest x-ray. But malignant disease was diagnosed in only 27 of the CAT scan-detected nodules and seven of those found on chest x-ray. Overtreatment was avoided by repeat scans a few months later and performing a biopsy only when the nodule grew. Also, two doctors read each scan.

Dr. Henschke and colleagues acknowledged the limitations of their study stating, "We have not yet followed up all our participants with malignant disease to determine cure." An 80% survival rate is not the same as an 80% cure rate. It is possible that the CAT scan merely allowed some or most of the people with malignant nodules to know about their cancer earlier. Until more is known, there is a concern that CAT scans would be used for screening by physicians who are not so skilled or cautious as those who conducted the New York/Montreal study.

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