CT screening appears to find early-stage lung cancers that would not have been detected with chest x-ray, enabling CT-screened patients to live significantly longer, concludes a new study from Japan.
Early detection and resection of lung cancers may offer the best hope of a cure, although previous studies using chest x-ray and sputum cytology in smokers have failed to show a reduction in mortality, wrote lead author Dr. Riken Kawachi and colleagues from the National Cancer Center Hospital in Tokyo. In several recent studies, CT has been shown to detect lung cancers at an earlier stage, though a mortality reduction has not been proved to date.
“The objective of the present study was to identify the characteristics of lung cancer detected by screening, and to clarify whether the screen-detected (SCR) group shows better survival than other groups,” they wrote. “The objective of the study was to compare screen-detected cancers to incidental (INC) or symptomatic cancers and to evaluate survival in these groups” (Journal of Thoracic Oncology, May 2009, Vol. 4:5, pp. 1-5).
The retrospective study evaluated the records of 2,281 patients who underwent lung resection for primary lung cancer between 2000 and 2006, classifying patients into three groups according to detection method: screening (n = 1,290), symptom-detected (SYM) (n = 481), and incidental (n = 568).
In the screening group, the researchers analyzed clinicopathological factors according to the detection modality: chest x-ray (n = 1,136, 82.6%), CT (n = 196, 13.9%), PET (n = 22, 1.6%), and sputum cytology (n = 17, 1.3%).
The results showed that screen-detected lung cancers were smaller in diameter (? 2 cm: 42.6%), less advanced (pathologic stage I: 70.8%), and had a higher incidence of adenocarcinoma (85.8%) compared to all detected lung cancers. Incidentally detected lung cancers were similar to those found at screening, while symptomatic cancers were larger and more advanced.
In particular, cancers detected by CT were smaller (? 2 cm: 76.4%), less advanced (clinical stage I: 97.2%; pathologic stage I: 93.1%), and more frequently adenocarcinomas at histology (92%) than cancers overall, Kawachi and colleagues reported.
The overall five-year survival rate was 75.4% for the 2,281 patients who underwent lung resection for primary lung cancer. Broken down by detection method, five-year survival rates for screening, symptomatic, and incidental groups were 79.6%, 74.6%, and 64.6%, respectively. The differences between the three groups were statistically significant (p = 0.0127).
Of 2,281 total patients, 1,486 had pathologic stage I non-small cell lung cancer. In this group, five-year survival overall and in the SCR, SYM, and INC groups were 89.6%, 92.9%, 84.0%, and 84.6%, respectively.
Detection modality affects survival
The detection modality was associated with significant differences in survival. Five-year survival rates for chest x-ray, CT, PET, and sputum cytology were 77.8%, 91.2%, 90.9%, and 80.9%, respectively. The difference in survival between the detection modalities was significant (p = 0.0127).
Of 896 patients with pathologic stage I non-small cell lung cancers, the overall five-year survival rates for chest-x-ray-detected and CT-detected cancers were 81.4% and 91.7%, respectively (p [ 0.0001).
Screening lung cancers were not only smaller (? 2 cm in diameter: 42.6%) and found at a lower stage (stage I: 73.0%), but also more often were adenocarcinoma (85.8%) than symptomatically detected lung cancers, the authors noted. “In particular, such findings were more evident with CT in the SCR group (2 cm or less in diameter: 76.4%, pathologic stage I: 93.1%, and adenocarcinoma: 92.6%),” they wrote.
The characteristics of screened lung cancers were similar to those of other studies (I-ELCAP reported an 85.1% incidence of stage I lung cancers, for example); however, the present study was unique in that it did not limit participation to smokers and former smokers.
Kawachi and colleagues also found a high incidence of adenocarcinoma in the screening group (85.8%), particularly in the CT-detected subgroup (92.6%). The incidence of bronchioloalveolar carcinoma (? 2 cm) in CT-detected lung cancers was 22.2%, significantly higher than in the chest x-ray group.
Five-year survival among the 1,290 screen-detected patients was 79.6%, and the five-year survival rate for patients with pathologic stage I cancer was 91.7%.
Limitations included the retrospective design of the study, and the fact that results were limited to patients who underwent resection. And although CT detected earlier-stage cancers and, therefore, offered better survival, the figures could reflect lead-time bias and length bias rather than a mortality reduction, the authors cautioned.
Still, the results, like those of previous trials including I-ELCAP (Henschke et al) and Kaneko et al, suggest that screening with low-dose helical CT “may be able to improve the efficacy of screening in terms of reducing lung cancer mortality,” the authors wrote.
Screening lung cancers in the study were characteristically less advanced, had a smaller diameter, and were more frequently adenocarcinoma histologically. By detecting earlier-stage cancers, CT may “improve the prognosis of lung cancer patients,” the authors concluded.