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Intense Lung Cancer Screening of Smokers Does Not Save Lives

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     (August 15, 2000) A follow-up of the Mayo Lung Project (MLP) reinforces the conclusion published in the 1986 that there is no life-saving benefit of frequent screening of smokers for lung cancer. Perhaps more importantly, these latest findings suggest that aggressive screening for lung cancer could do more harm than good.

     The MLP, funded by the National Cancer Institute (NCI) and conducted by the Mayo Clinic, was a randomized, controlled clinical trial conducted between 1971 and 1983 that involved two groups of male smokers. The 4,618 men in the "intervention arm" were reminded to get a free chest x-ray and sputum cytology every four months over a period of six years, while 4,593 men in the "usual care arm" simply got a recommendation that they undergo the same screening once a year.

     Despite the initial findings of the MLP, Pamela Marcus, Ph.D., an epidemiologist in NCI's Division of Cancer Prevention, tells cancerpage.com she was "a little surprised" by what she and her colleagues discovered when they analyzed data an average 20 years after participants entered the study.

     They found four-point-four lung cancer deaths per 1,000 person years in the intervention group and three-point-nine deaths per 1,000 years in the usual care group. Marcus notes that the difference is not statistically significant. " But even so, you generally don't want to see things in that direction. They imply that a screening tool actually did some harm."

     To Marcus, these latest findings suggest that a number of tumors identified as a result of the MLP that would not have been found without screening never caused any serious illness or death.

     "Generally people don't think of lung cancer as a disease that's innocuous. Most everybody who's diagnosed with lung cancer dies of lung cancer. So we don't think about lung cancer as one of those diseases that people easily survive. We don't think about people walking around with growths in their lungs that aren't harmful or don't have harmful potential."

     Marcus points to the realization that not every positive screen for prostate cancer requires immediate treatment, that sometimes "watchful waiting" is the preferred course.

     "Before screening programs were implemented, we didn't know very much about these lesions with limited clinical relevance. There's no reason to believe that wouldn't be the case in lung cancer also," says Marcus.These latest findings from the MLP, reported in the August 16, 2000, Journal of the National Cancer Institute, come amid increased promotion of spiral computed tomography (CT) as an early detection of lung cancer screening test. Spiral CT is routinely used for determining the stage of cancer after diagnosis. It can produce a three-dimensional model of the lungs from a 20-second x-ray of the entire chest during which the patient absorbs about the same radiation as absorbed from a mammogram.

     Marcus is skeptical. She calls results from early, short-term tests "very promising," but says, "the bottom line is that you have to make sure with any screening tool that the benefits outweigh the harms, and there hasn't been any evidence with spiral CT yet that the benefits outweigh the harms."

     "If these lesions with limited clinical relevance exist, spiral CT is going to pick them up. And in picking them up, you have to treat them and you may very well do harm." She points to the potential risks of biopsies and surgery resulting from such screenings.The NCI is about to launch a feasibility study, to be concluded by next summer, to determine whether a large-scale, randomized, controlled clinical trial of CT scan screening can be conducted with lung cancer mortality as the endpoint.

     Separately, an NCI-funded study designed to be more definitive about the benefits of annual chest x-ray screening began six years ago and is expected be completed by 2015. It is much larger than the MLP, with nearly 150,000 participants, and includes women.

     "We may eventually know that screening with chest x-ray modestly reduces your risk of lung cancer mortality," says Marcus, "but at this point we don't know, and I think that it's okay to admit that we don't know."

     In an editorial in the same issue, Dr. William C. Black of the Department of Radiology at Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire, spells out the dangers of "overdiagnosis" that he sees in cancer screening. In addition to randomized clinical trials, he suggests a mandatory observation period for small nodules and a "balanced presentation" to patients or prospective participants in screening trials about the potential benefits and risks, including the risk of overdiagnosis.

     SOURCE:Journal of the National Cancer Institute, August 16, 2000; 92:1308-16 (Editorial, 1280-82) Content Provided By: CancerPage.com

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