Screening for lung cancer

Modeling excess lung cancer risk among screened arm participants in the Mayo Lung Project

BACKGROUND

The Mayo Lung Project (MLP) was a randomized clinical trial designed to test whether periodic screening by chest x-ray reduced lung cancer (LC) mortality in men who were high-risk smokers. Among MLP participants, there were more deaths from LC in the screening arm both at the trial's end and after long-term follow-up. Overdiagnosis was cited widely as an explanation for the MLP results, whereas a role for excess LC risk attributable to undergoing numerous chest x-ray screenings largely was unexamined. The authors of this report examined the consistency of the MLP data with a modified 2-stage clonal expansion (TSCE) model of excess LC risk.

METHODS

By using a simulation model calibrated to the initial MLP data, the authors examined the expected statistical variance of LC incidence and mortality between the screening and control arms. A Bayesian estimation framework using a modified version of the TSCE model to evaluate the role of excess LC risk attributable to chest x-ray screening was derived and applied to the MLP data.

RESULTS

Simulation experiments indicated that the overall difference in LC deaths and incidence between the study arm and the control arm was unlikely (P = .0424 and P = .0104, respectively) assuming no excess risk of LC. The authors estimated that the 10-year excess LC risk for a man aged 60 years who smoked and who received 10 chest x-ray screenings was 0.574% (P = .0021).

CONCLUSIONS

The excess LC risk observed among screening arm participants was found to be statistically significant with respect to the TSCE model framework in part because of the incorporation of key risk correlates of age and screen frequency into the estimation framework.

Incidental lung cancers identified at coronial autopsy: implications for overdiagnosis of lung cancer by screening

BACKGROUND

The extent to which overdiagnosis occurs in lung cancer screening programmes has been debated. Overdiagnosis refers to the detection by screening of cancers that would not have become clinically apparent or symptomatic before that individual died of other causes.

METHODS

A retrospective review of coronial autopsies performed in Victoria between April 1991 and February 2002 was conducted to determine the rate of incidental lung cancer in individuals who died of natural causes.

RESULTS

A total of 24,708 autopsy reports were searched electronically. We estimated that in 56% of these death was from natural causes. Amongst individuals who died naturally there were 167 cases of lung cancer, 47 of these were incidental including five carcinoid tumours, three small cell tumours, 11 cases of carcinoma in situ and 28 invasive nonsmall cell lung cancers. Of the incidental invasive nonsmall cell lung cancers, 86% were stage I.

CONCLUSIONS

Although incidental lung cancer is uncommon, there are some lung cancers that remain undetected during life and do not contribute to death. These findings support the hypothesis that some lung cancers detected by screening may never progress to cause symptoms or death in that individual's lifetime and therefore may be overdiagnosed by screening.

New concepts in lung cancer screening

Although spiral CT has an undeniably impressive ability to detect occult lung cancers in asymptomatic smokers, it is not clear whether screening this patient group will lead to a reduction in disease-specific mortality. The specter of overdiagnosis in lung cancer screening, which manifested during the chest radiograph trials of the 1970s and 1980s, still hangs over screening regimes today. The detection of premalignant lesions by molecular medicine techniques and fluorescence bronchoscopy may allow the development of novel treatments for preinvasive disease, but it is likely that radiologic means of detection will form the front line of any near future screening program. The proposed screening techniques may be new, but their use must be tested against tried and trusted standards of medical practice.

Early lung cancer action project: annual screening using single-slice helical CT

The advent of helical CT imaging held promise for the early diagnosis, and thereby, for enhanced curability of lung cancer--a highly fatal disease. In 1993, the Early Lung Cancer Action Project (ELCAP) was initiated and experimentally screened a cohort of 1,000 high-risk persons. Here we summarize the results of the baseline and annual repeat CT screening of these 1,000 subjects. CT-based screening (compared to traditional radiology) was clearly shown to enhance the detection of lung cancer at earlier and more curable stages. A discussion follows of the meaning of the results and possible future screening protocols.

CT screening for lung cancer: coping with nihilistic recommendations

The practicing radiologist today is well persuaded that earlier diagnosis of lung cancer can be achieved with traditional-type radiography and especially with modern computed tomography. The practitioner also is confident that intervention in the context of earlier diagnosis is more effective in preventing death due to this otherwise fatal disease. The practitioner is thus inclined to consider such screening in a high-risk person with suitably long life expectancy, especially when asked to provide it. On the other hand, the practitioner is aware of official recommendations against lung cancer screening, said to be based on demonstrated lack of effectiveness of traditional radiographic screening. Some researchers have expressed concerns about screening-associated "overdiagnosis." Given this dilemma, the critically thinking practitioner is concerned to understand the foundation of the official nihilism in evidence and reasoning, as she or he suspects that something may be seriously wrong in this. This article is an attempt to help such a practitioner in this effort--an effort that in the end is rewarded by the comforting realization that the nihilistic recommendations and hesitation-provoking cautions are founded on pseudoevidence and specious reasoning.

CT screening for lung cancer

Recommendations against screening for lung cancer were based on the lack of a reduction in mortality of the screened group as compared with the control group in randomized control trials. These results were interpreted as showing that early detection of lung cancer as a result of screening did not decrease the mortality rate compared with detection after presentation of symptoms for the populations being screened. Evidence, however, shows that earlier-stage intervention leads to substantially higher rates of survival. Screening, therefore, is an effective means to prevent deaths from this otherwise fatal disease. This article discusses the evidence of both CT and chest radiograph screening.

Screening for lung cancer

Screening for lung cancer serves to prevent deaths from this disease insofar as earlier resections are associated with higher rates of cure. There is good reason to believe that this is the case: in stage I, the 5-year survival rate with resection is 70%, whereas without resection the corresponding rate is only 10%. Before this evidence emerged, various authoritative organizations and agencies in North America advised against screening for lung cancer on the grounds of the results of several RCTs. As for CXR, I argue that the study results are consistent with up to 40% reduction in the fatality rate. Moreover, modern helical CT screening provides for detecting much smaller tumors than were detected in those studies. It is time to revoke the conclusion that screening for lung cancer does not serve to prevent deaths from this disease, and to quantify the usefulness of CT screening in particular. As for the requisite research, the prevailing orthodoxy has it that RCTs are to be used, but I argue that more meaningful results are obtainable, more rapidly and much less expensively, by the use of noncomparative (and hence unrandomized) studies.