Impact of low-dose CT on lung cancer screening

Our plain-English summary of Impact of low-dose CT on lung cancer screening, by S. Diederich, D. Wormanns (Lung Cancer, 2004).

The study

• Authors: S. Diederich, D. Wormanns
• Journal: Lung Cancer
• Published: 2004;45 Suppl 2:S13-9
• Type of article: Review
• Cited by: 38 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Despite advances in therapy, the prognosis of lung cancer remains dismal due to the fact that most cases of lung cancer are diagnosed at advanced stages, when the chance of cure is poor. In cases detected at early stages prognosis is better. Unfortunately, early lung cancer usually causes no symptoms and is, consequently, rarely diagnosed. Therefore, screening for early asymptomatic lung cancer with diagnostic procedures appears promising particularly as risk factors for lung cancer are well known (cigarette smoking, occupational asbestos exposure and others) and screening could, therefore, focus on these risk groups. In the past, screening trials using analysis of sputum cytology and to some extent chest radiography have failed to demonstrate a reduction in lung-cancer mortality with screening, probably due to insufficient sensitivity of these tests for early lung cancer. During the last decade the introduction of spiral computed tomography (CT) has provided a technique with a much higher sensitivity for small lung cancers. Feasibility studies using low-radiation-dose CT demonstrated a high proportion of non-small-cell lung cancer at the initial examination (prevalence) with decreasing numbers of detected cancers at follow-up (incidence). The proportion of early-stage tumors was high both at prevalence and incidence examinations. The rate of invasive procedures for benign lesions was low; most indeterminate lesions could be classified with non-invasive diagnostic approaches. The proportion of interval cancers (cancers diagnosed by symptoms between two screening CT scans) was low. As, however, these one-arm feasibility trials are not appropriate to assess a potential mortality reduction through CT screening, prospective randomised multicenter trials were recently initiated in several countries to analyse the effect of CT screening on lung-cancer mortality.

In plain English

This review of low-dose CT lung cancer screening, by two authors from German radiology departments, reported no new data. The authors named smoking and occupational asbestos exposure as risk factors for targeting screening, without asbestos-specific results. It summarised seven one-arm feasibility studies (Japan, USA, Germany, Italy), mostly in smokers. Prevalence results in its table showed lung cancer at CT in 0.43% to 2.7% of volunteers; ALCA's lowest figure included 5 of 15 cancers from second or later annual CTs. Stage I made up 55% to 93% of those non-small-cell cancers. The authors stated follow-up incidence was lower than prevalence, though some studies' counts were not. Using classification rules, procedures revealing benign lesions were about 20–30% of invasive procedures. A hypothetical calculation for 100,000 people aged 60 to 70 (assuming 1% incidence, linear radiation risk, 1.5 scans yearly at 1 mSv) set 4.5 induced cancers a year against 200 lives saved if lung-cancer mortality fell from 85% to 65%. The authors concluded these trials could not show whether screening reduces deaths; randomised trials had begun in several countries.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: narrative review of feasibility studies of low-dose CT lung cancer screening
• Who was studied: Seven one-arm feasibility screening studies (ALCA, Shinshu, ELCAP, Mayo, Münster, Milan, Hitachi), mostly in smokers. In the table's prevalence results, each listed between 817 and 7956 volunteers.
• Exposure: Screening with low-radiation-dose spiral CT in groups at risk of lung cancer. The authors name cigarette smoke and occupational exposure to asbestos as risk factors. No asbestos-exposed group is reported separately.
• Main results:
  • In the table's prevalence results, ELCAP had the highest proportion of lung cancer detected at CT: 27 of 1000 volunteers (2.7%).
  • ALCA had the lowest proportion in the prevalence results, 15 (0.43%). Of these 15 cancers, 5 were detected at a second or later annual CT, so this figure is not a first-round rate.
  • Among non-small-cell lung cancers in the prevalence results, the proportion at stage I ranged from 6 (55%) in Milan to 14 (93%) in ALCA.
  • The authors stated that incidence (cancers found at follow-up scans) was lower than prevalence. In the table, however, follow-up cancer counts were not lower in every study: ALCA had 22 at follow-up against 15 at prevalence, and Milan had 11 at both.
  • The proportion of stage-IA and resectable lung cancer was much higher than in populations presenting with symptoms.
  • When diagnostic rules were used to classify nodules, invasive procedures that revealed benign lesions were about 20–30% of all invasive procedures.
  • The proportion of cancers diagnosed by symptoms between two screening scans (interval cancers) was lower.
  • The authors made a hypothetical calculation for 100,000 subjects aged 60 to 70. It assumed a linear radiation risk, an average of 1.5 low-dose CT scans per year at 1 mSv each, and a natural lung-cancer incidence of 1%. On these assumptions it estimated 4.5 radiation-induced cancers per year, against 200 lives saved if lung-cancer mortality fell from 85% to 65%.
• The authors' conclusion: The authors concluded that one-arm feasibility trials cannot show whether CT screening reduces lung-cancer deaths. They noted that prospective randomised multicentre trials had been started in several countries to answer this.
• Limitations the authors state:
  • Survival gains seen in the feasibility trials may reflect lead-time, length-time and overdiagnosis bias. The authors say the effect of these biases cannot be quantified.
  • Data on radiation-induced cancer risk come from high exposures. It is unknown whether they apply at low screening doses.
  • Spiral CT has low sensitivity for purely endobronchial lung cancer.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Low-Dose CT Screening, Prognosis, Lung Cancer, Asbestos Exposure, Sputum, Cytology, CT Scan.

Related studies

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• Yield of Low-Dose Computerized Tomography Screening for Lung Cancer in High-Risk Workers: The Case of 7189 US Nuclear Weapons Workers — S.B. Markowitz, A. Manowitz, et al. (2018)
• Lung cancer screening with low-dose CT — S. Diederich, D. Wormanns, et al. (2003)
• Psychological impact of computed tomography screening for lung cancer and occupational pulmonary disease among asbestos-exposed workers — T. Vierikko, S. Kivistö, et al. (2009)
• Asbestos Surveillance Program Aachen (ASPA): initial results from baseline screening for lung cancer in asbestos-exposed high-risk individuals using low-dose multidetector-row CT — M. Das, G. Mühlenbruch, et al. (2007)
• Smoking, occupational risk factors, and bronchial tumor location: a possible impact for lung cancer computed tomography scan screening — M. Gonzalez, J.M. Vignaud, et al. (2012)

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