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Vol.49 No.4 contents | Japanese/English |
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- The 23rd Lung Cancer Mass Screening Seminar -
CT Screening for Lung Cancer: Update 2008
Claudia I. Henschke1, Rowena Yip1, David F. Yankelevitz11Department of Radiology, New York Presbyterian Hospital-Weill Medical College, New York
Screening for a cancer should be considered when the cancer is significant in terms of incidence and mortality, treatment of early stage disease is better than treatment of late stage disease, and there is a screening regimen that provides for earlier diagnosis rather than later, symptom-prompted diagnosis. Lung cancer qualifies as it kills more people than any other cancer worldwide. In the United States it kills more people than colon, breast, and prostate cancer combined and more women than breast cancer. The fundamental concepts of screening are presented. Screening for a cancer is a repetitive process, starting with the baseline round followed by repeat rounds of screening at set intervals. The regimen of screening defines the initial diagnostic test and the sequence of tests to be performed leading to a rule-in diagnosis of the cancer. The regimen should provide lead time of the diagnosis of the cancer. The regimen for the first, baseline round may be different from the regimen for the repeat rounds as the former is inherently different from the subsequent repeat rounds. Baseline screening identifies a greater proportion of cancers with a longer latent (asymptomatic) phase than repeat screening, called length bias. Length bias exists for any screening program, regardless of the design of the study or the cancer. Repeat rounds of screening identify the same proportion of cancer diagnoses found in absence of screening for people having the same risk of the cancer and these repeat rounds of screening can be pooled. It is also a consequence of length bias that cancers found in repeat rounds are earlier in their latent phase than those of the baseline round, a less frequently mentioned consequence. Overdiagnosis bias, another bias of screening, can occur in two ways: 1) a 'cancer' detected by the screening, pathologically proven, that is not life-threatening even when not resected and 2) a genuine life-threatening cancer that is diagnosed and treated but the person dies of another disease or accident. This bias can be addressed in various ways, including by the regimen of screening and by following those who refuse treatment. As screening is pursuit of early diagnosis followed by early treatment, both the diagnostic and treatment performance can be addressed separately. Key diagnostic performance measures of the regimen are: 1) the proportion of screen-diagnoses among all diagnoses and 2) the stage distribution of the diagnosed cancers. These performance measures are unaffected by the frequency of lung-cancer diagnoses and thus also unaffected by the enrollment criteria. The key prognostic performance measure is the curability rate which is provided by the long-term follow-up of all diagnosed cases of lung cancer, regardless of stage and treatment. It can also be estimated by the proportion in Stage I multiplied by the curability rate in Stage I. Finally this report provides a summary of the diagnostic and prognostic performance measures available from the screening trials to date.
key words: CT Screening for Lung Cancer, Early Lung Cancer Action Project (ELCAP), New York-ELCAP (NY-ELCAP), International-ELCAP (I-ELCAP)
JJLC 49 (4): 477-490, 2009
