Lung Cancer Screening

Lung cancer screening is not recommended on a population basis due to lack of evidence that any available screening procedure, even for smokers, can identify tumors early enough to reduce mortality. This remains a major challenge to research and technology because of the tremendous burden caused by this cancer, including among ex-smokers. In 2003, there were estimated 171,900 new cases and 157,200 deaths, making it by far the most common killer from cancer in men and in women.

None of the four randomized trials conducted during the 1960s and 1970s reduced mortality significantly over no screening. The Mayo Lung Project, the primary trial contributing to this evidence, demonstrated that screening with either chest x-rays or chest x-rays plus sputum cytology lowered the stage at presentation and increased survival, but neither approach had any effect on lung cancer mortality. Although lack of connection between improved survival and the absence of a mortality benefit can be attributed to lead-time and length biases, these studies have been criticized for other methodologies reasons. Extended mortality follow-up of participants in the Mayo Lung Project suggested that over diagnosis, the identifications of clinically unimportant lung cancer lesions might have occurred.

Low-dose CT scanning is a new and potentially efficacious method for early detection of lung cancer. This noninvasive technique, which creates an image of the entire thorax during a single held breath with a low radiation dose, is being offered by an increasing number of imaging facilities for older smokers and former smokers. However, to date, evidence of high sensitivity comes only from observational studies that are susceptible to lead-time and length-time bias. The possibility of over diagnosis and concerns of harm from CT screening have also been raised, and there is, as yet, insufficient evidence to support mass lung cancer screening with this procedure. Nevertheless, the potential of this technology and the enormous societal burden imposed by lung cancer motivated the NCI to begin a large, randomized controlled trial to assess the effect of low dose CT screening are ongoing and may add to the evidence produced by the NCI-supported trial, which will take approximately 10 years to produce results. Meanwhile, decisions about use of CT scans for lung cancer screening remain a matter of individual judgment between physicians and patients. Several reports suggest the need for caution in adopting lung CT screening, especially in view of aggressive direct-to-consumer marketing of the procedure. In a detailed decision analysis, Mahadevia et al showed that even if efficacy of helical CT is shown, it is unlikely to be cost effective. Like many tests, helical CT may be able to identify small lesions. However, questions remain about the mortality impact and cost effectiveness. Thus, the ongoing trial is of critical import. Efforts to prevent initiation, especially by youth, and cessation of tobacco use remain the physicians best tool for combating lung cancer.