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#78 Lung Cancer Screening – Low dose CT, High dose False Positives

Does screening high-risk individuals with low dose CT (LDCT) result in reduced lung cancer mortality?

Benefit from screening for lung cancer with LDCT has been demonstrated in only one trial, without a “usual care” group. The high number of false positives, which require further, sometimes invasive investigations, is worrisome. Smoking cessation should remain the priority to decrease lung cancer mortality.

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National Lung Screening Trial (NLST), 53,454 current or former smokers (at least 30 packyears), aged 55-74 years without history of cancer. Randomized to three annual screening exams with LDCT or chest x-ray (CXR), followed for an additional five years.1
  • Lung cancer mortality: 1.3% LDCT versus 1.7% CXR.
    • Number Needed to Screen (NNS)=306 to prevent one lung cancer death over eight years. 2
  • Overall mortality: 7.0% LDCT versus 7.5% CXR, NNS=217.
  • Concerns:
    • Amongst the 26,309 patients screened with LDCT, there were a total of 18,146 positive LDCTs.
      • 96.4% of positive LDCTs were false positives.
    • Possible over diagnosis of cancers that would never have become clinically important.
    • No placebo group.
Two smaller Randomized Controlled Trials (RCTs) showed no difference in lung cancer mortality when annual LDCT screening was compared to:
  • Baseline CXR and sputum, then yearly medicals.3
    • 2472 patients, 34 month follow up: Relative Risk (RR)=0.97 (CI 0.71-1.32).
  • Annual questionnaires and lung function testing.4
    • 4104 patients, 58 month follow-up: RR=1.15 (CI 0.83-1.61).
  • Screening with CXR does not reduce lung cancer mortality.5,6
  • Positive LDCTs require further investigations (i.e. additional imaging, bronchoscopy or needle biopsy).1,3,4,7
    • Complications of transthoracic needle biopsy include hemorrhage (1%), pneumothorax (15%) and pneumothorax requiring chest tube (6.6%).8
  • Estimates of LDCT radiation harm: one additional cancer death per 2500 persons screened annually for three years.9
  • The American Lung Association and others now recommend LDCT screening for high risk individuals. 10,11
  • A 65 year-old male smoker has a 5.9% risk of dying from lung cancer in the next 10 years compared to a 0.4% risk for non-smokers.12 This risk declines with smoking cessation.13

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  • Christina Korownyk MD CCFP
  • Mark McConnell MD ABIM

1. National Lung Screening Trial Research Team. NEJM. 2011; 365:395-409.

2. Gross CP. ACP Journal Club. 2011; 155:JC5-6.

3. Infante M, Cavuto S, Lutman FR, et al. Am J Respir Crit Care Med. 2009; 180:445- 53.

4. Saghir Z, Dirksen A, Ashraf H, et al. Thorax. 2012; 67:296-301.

5. Manser RL, Irving LB, Stone C, et al. Cochrane Database Syst Rev. 2004; 1:CD001991.

6. Oken MM, Hocking WG, Kvale PA, et al. JAMA. 2011; 306:1865-73.

7. Swensen SJ, Jett JR, Hartman TE, et al. Radiology. 2005; 235:259-65.

8. Wiener RS, Schwartz LM, Woloshin S, et al. Ann Intern Med. 2011; 155:137-44.

9. Bach PB, Mirkin JN, Oliver TK, et al. JAMA. 2012; 307:2418-2429.

10. American Lung Association. 2016. Available at: Accessed Dec. 13, 2016.

11. Jaklitsch MT, Jacobson FL, Austin JH, et al. J Thorac Cardiovasc Surg. 2012;144:33- 8.

12. Woloshin S, Schwartz LM, Welch HG. J Natl Cancer Inst. 2008; 100:845-53.

13. Godtfredsen NS, Prescott E, Osler M. JAMA. 2005; 294:1505-10.

Authors do not have any conflicts of interest to declare.