Cancer Screening's Next Chapter: Mobile CT Scanning for Lung Cancer
ABSTRACT & COMMENTARY
Synopsis: In this report, a group of Japanese investigators have found that use of a mobile CT unit to screen 3969 healthy volunteers effectively led to the diagnosis of small lung cancers in 19 individuals. The mean diameter of the discovered tumors was 17 mm, and 16 of the 19 were Stage I after surgery. Conventional chest x-ray detected only eight of the 19 tumors. Sone and colleagues conclude that CT technology can be effectively applied to lung cancer screening. This novel approach needs more extensive analysis, particularly as it relates to survival and cost.
Source: Sone S, et al. Lancet 1998;351:1242-1246.
Lung cancer remains a major cause of cancer mortality worldwide. One important reason for the high death rate is that patients are nearly always diagnosed with locally advanced or metastatic disease. Effective screening must include a diagnostic technique that detects cancers at an early stage. Routine chest radiography and sputum analysis have not proven effective in this regard. In this report from Shinshu University School of Medicine in Matsumoto, Japan, 3967 volunteers (aged 40-74 years) from a mostly rural region of Japan with a low lung cancer incidence were screened using a spiral computed tomography (CT) scanner and miniature fluorophotography during nine months in 1996. Both CT and fluorophotography units were housed in a truck. The individuals were drawn from a well characterized data base of individuals screened every year by chest x-ray and sputum cytology as part of a regional health program.
The CT scan results were classified as normal (64%), abnormal lung but of little clinical consequence (24%), abnormal lung but not cancerous (4%), lesion identified, probably non-cancerous but suspicious (1%), lesion identified, suspicious for cancer (2%), and indeterminate nodule (2%). Of the 1% (n = 59) classified as probably non-cancerous but suspicious, further workup (including conventional chest x-ray and conventional CT) revealed cancer in three individuals, which was confirmed at surgery. Of the 2% (n = 84) that were considered suspicious for cancer, further workup resulted in 14 cases of lung cancer diagnosis. All but one were resected. That one patient was found to have metastatic disease and did not have thoracotomy. Of the 69 others in this group, 59 were found to have non-neoplastic lesions, five had normal lungs, and five were followed using repeat CTs at three-month intervals because of indeterminate nodules. Of the 80 individuals who had indeterminate lesions detected by the spiral CT, two were diagnosed as cancer and were confirmed at surgery.
Among the 19 patients discovered to have lung cancer in this series, only eight had lesions visible on conventional chest x-ray. Thoracotomy was done on 21 subjects and 18 were found to have cancer (3 others had inflammatory lesions). The mean diameter of the lung tumors (by CT scan) was 17 mm (range, 6-47 mm). Well differentiated adenocarcinoma was found in 11, poorly differentiated adenocarcinoma in one, squamous cell carcinoma in two, bronchioalveolar carcinoma in two, and adenosquamous carcinoma in one. Of the 19 patients, 16 were American Joint Committee Stage I (by postsurgical staging) and three were Stage IV.
Sone and colleagues conclude that CT was more accurate than chest x-ray and led both to early detection and accurate diagnosis of lung cancer. The costs associated with the screening were not examined.
COMMENTARY
Effective screening for lung cancer would be a major advance. Unfortunately, previous efforts in normal or high-risk individuals (using chest x-ray or sputum analysis) have failed to reveal any survival advantage for patients detected through screening.1-4 The failure of screening to exert an influence on survival is primarily because lesions detected by screening are often advanced beyond curative possibility. Detection of earlier lesions would require a more sensitive technique. Clearly, conventional CT is more sensitive, but the idea of doing large-scale screening using this technique would overwhelm existing resources, even if only applied to high-risk individuals.
However, the spiral CT may provide the technological compromise. The equipment is smaller, faster, and presumably less costly. The current report is the first step in demonstrating a screening strategy that uses this sensitive technique to a large population. The results indicate that the spiral CT unit can detect small or poorly visible lung cancers at an early stage. They also clearly demonstrate the limitations of chest radiography as a screening procedure.
Critical questions remain. Would this procedure be useful in high-risk patients? How frequently should patients be examined, and what is the cost for detecting a curable patient? More importantly, does the recognition of early cancers, as described in this study, translate into increased survival and an enhanced cure rate? Sprial CT scanning could improve survival if the reported data are reproduced on a larger scale, but the data aren't in yet. Sone et al are continuing this ambitious project, and perhaps their findings will change the way we think about, and practice, lung cancer screening.
References
1. Melamed MR, et al. Chest 1984;86:44-53.
2. Fontana RS, et al. Am Rev Respir Dis 1984;130: 561-565.
3. Berlin NI, et al. Am Rev Respir Dis 1984;130:545-549.
4. Fontana RS, et al. Cancer 1991;67:1155-1164.
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