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In Reply:

Duke University Medical Center, Durham, NC, and the Mayo Clinic, Rocheser, MN

In our recent study,¹ we constructed a model to predict outcomes, and by definition needed to make a number of assumptions. We used a simple, but unconventional, approach because it is impossible to otherwise calculate these statistics from current observational trial data. Dr Tockman suggests that this will lead to an improbable projection, but provides no details on the assumptions that he finds objectionable.

We agree that stage shift is an important and interesting feature of screening trials, and in fact there are several paragraphs on the subject in the Discussion section of our article. Dr Tockman states that the Early Lung Cancer Action Project (ELCAP) found 9.6 new cancers per 1,000 person-years, but to date, ELCAP has only reported in the peer-reviewed literature their prevalence and first-year incidence data with a total of 36 cancers (27 prevalence and nine incidence cases) and 1,841 person-years. This is equivalent to 19.5 new cases per 1,000 person years.

We also agree that not all computed tomography (CT) -detected cancers may be fatal (permitting overdiagnosis), but this was accounted for in the model when we used stage-specific survival rates (the inverse of fatality). Not all patients are predicted to die from their disease. It is believed, although not clearly proven, that screening will not change stage-specific survival rates, but that the effect of screening will be to shift the distribution of patients from late-stage to earlier-stage disease. It is this theoretical shift that will account for the decrease in mortality, and without it there will be no effect on outcomes.

Dr Tockman reports a comparison of late-stage disease between the old Mayo study to the current CT trials. When we search the published literature, we could not find appropriate matched-stage data in the Mayo Lung Project to determine stage shift over the same period of time as the CT trials. Although the data are normalized for person-years, without the primary published Mayo chest radiographic trial data, it is unclear how Dr Tockman's calculations were performed for that trial so that a meaningful comparison could be achieved.

We understand that modeling must make a number of assumptions, and although we used an unusual approach, we tried to be conservative. This may not be the optimal method, but this only reiterates the fact that despite the best theories and projections, appropriately designed clinical trials must be performed before the true utility of screening for lung cancer can be determined.

Authors' Disclosures of Potential Conflicts of Interest

The authors indicated no potential conflicts of interest.

REFERENCE

1. Patz EF Jr, Swensen SJ, Herndon JE: Estimate of lung cancer mortality from low-dose spiral computed tomography screening trials: Implications for current mass screening recommendations. J Clin Oncol 22:2202-2206, 2004[Abstract/Free Full Text]

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Related Correspondence

• Improbable Estimate of Lung Cancer Mortality From Screening Trials
  Melvyn S. Tockman
  JCO 2005 23: 2106-2107 [Full Text]

This Article Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Alert me to new issues of the journal Save to my personal folders Download to citation manager Rights & Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Patz, E. F. Articles by Herndon, J. E. Search for Related Content PubMed Articles by Patz, E. F., Jr Articles by Herndon, J. E. Related Articles Related Correspondence Social Bookmarking                            What's this?