Spiral Computed Tomography Screening for Lung Cancer Is Ready for Prime Time

James R. Jett

Mayo Clinic, Rochester, Minnesota

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More Americans die of lung cancer than from any other cancer. In 2000, it was estimated that there would be 164,000 new cases and 157,000 deaths (1). There are more deaths from lung cancer in the United States than from the three next most common cancer-related causes of death (colorectal, breast, and prostate). There has been a lack of improvement in 5-year survival from lung cancer since the mid-1970s, but significant improvement for the three next most common cancer killers. Why? A partial answer may be that we screen for colorectal, breast, and prostate cancer but not for lung cancer. The official position of the American Cancer Society is that there is no role for screening of lung cancer even in high-risk individuals.

In the 1970s the National Cancer Institute sponsored three large lung cancer screening trials (2). These trials evaluated chest roentgenogram and sputum cytology as screening modalities and failed to show a decrease in lung cancer mortality in the screened groups. On the basis of these three trials it was concluded that there was no role for any lung cancer screening.

In a report from the Mayo Clinic screening trial, 90% of peripheral carcinomas and 75% of perihilar carcinomas were visible in retrospect on older chest X-rays (5). Quekel and associates reported a 19% miss rate of peripheral lung cancer with chest radiographs and observed that the average size of the missed cancer was 1.6 cm (6). Sone and coworkers compared chest radiographs with spiral computed tomography (CT) scans in 44 cases of lung cancer detected in a spiral CT scan screening trial (7). The chest X-ray failed to detect 77% (34 of 44) of all cancers. Accordingly, by using chest radiographs for screening we miss the majority of lung cancers  2 cm in diameter (5).

The earliest report of the use of low-dose spiral CT scan for screening was from Kaneko and coworkers (8). They detected 15 cases of lung cancer and the chest radiograph in 11 of these individuals was negative. In a more recent update, these investigators report the detection of 42 lung cancers by spiral CT screening. The median diameter of the cancers was 1.5 cm and 34 (81%) were Stage IA (9). The 5-yr survival was 78%.

In 1999, a New York City group reported on their baseline screening results with low-dose spiral CT scans (10). They screened 1,000 volunteers and detected a lung cancer in 27 individuals by CT. The cancer was visible by chest radiograph in only seven. Twenty-two of the 27 lung cancers were Stage IA. In 15 of the 27 lung cancer cases, the tumor diameter was 10 mm or less (10).

A Mayo Clinic screening trial enrolled 1,520 individuals 50 yr of age or older, who had a smoking history of at least 20 pack-years (11, 12). As of October 2000 we detected 19 prevalence cancers (11). The histology of 2 indicated small-cell lung cancer; of the 17 non-small cell lung cancers (NSCLCs), 6 were  1 cm in diameter and 8 were 1.1-2.0 cm in diameter. Fifteen of the 17 NSCLC cases were Stage I or II (88%) and underwent resections with curative intent.

It is clear from these studies that spiral CT scans detect lung cancers at an average size of 1.5 cm or less. This size is usually missed on chest roentgenogram. Approximately 80% of these lung cancers are Stage IA as opposed to current medical practice, where only 15-20% are Stage IA.

One major concern is the high rate of detection of indeterminate nodules by spiral CT screening. In the New York series they detected noncalcified nodules in 23% of participants and in the Mayo series we detected at least one nodule in 51% (11). In the Mayo series, 89% of all nodules detected were 7 mm or less and of a size we judged safe to observe. These nodules necessitate follow-up scans. The optimal frequency of follow-up is being evaluated. Two new developments that are likely to be implemented in the next few years are a computer-aided diagnosis (CAD) system and volumetric nodule measurement (13, 14). The CAD system will aid the radiologist in the detection of small nodules and help decrease the miss rate (13). The volumetric measurement will provide a three-dimensional technique for volume determination that is superior at detecting growth of a nodule (14). One report has demonstrated that tumor doubling times of cancers can be determined with scan intervals as short as 30-40 days (14). With this automated system these tiny nodules will be accurately measured and the volume calculated. Documenting volumetric tumor growth by CT scans would eliminate the need for needle biopsies before surgery.

An additional concern about low-dose spiral CT scan screening is cost. A single scan from the sternal notch to iliac crest can be performed in 12-15 seconds. There is no contrast involved. Patients are in and out of the scanner quickly. At the Mayo Clinic, we are able to scan six patients in 30 min without difficulty. With this efficiency it is estimated that the actual cost of low-dose spiral CT screening may be reduced to the range of $150. When a nodule(s) is detected this necessitates follow-up tests. Even when these follow-up scans, biopsies, and surgery for lung cancer are considered, one group of investigators has estimated the cost effectiveness for lung cancer screening to be less than $10,000/yr of life saved (15).

In conclusion, spiral CT scan screening for lung cancer is the single most exciting new development in lung cancer that I have witnessed in my 20-year career (12). It offers us the hope of significantly increasing lung cancer survival and decreasing mortality. Even though there are issues of cost and mortality reduction that need to be elucidated, I would recommend spiral CT scan screening for my brother or sister if he/she were a current or former smoker.

	References

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