Lung cancer screening

Lung cancer screening with low-dose CT (LDCT) is an imaging strategy that is beginning to be adopted for high-risk patients in some health systems. Lung cancer is the most common cause of cancer death worldwide, and there is accumulating higher level evidence that a mortality benefit exists with the screening of carefully selected patients.

A Lung-RADS screening classification exists for the purpose of standardizing follow up and management.

Screening guidelines

American Lung Association low-dose CT lung cancer screening recommendations (based on National Lung Screening Trial criteria) ⁵:

• current or former smokers with at least a 20 pack-year history of smoking
• 50-80 years of age
• no history of lung cancer

Other recommendations:

• smoking cessation must be emphasized for patients who are being screened 
• imaging screening programs should be associated with multidisciplinary centers that can care for patients who need follow-up
• screening should not be mandatory, but the patient may choose it after a discussion of risks and benefits

Advantages to screening

• detection of lung cancers at an early stage leads to a better outcome (~52% 5-year survival at stage I and 5% 5-year survival at stage IV)
  • potential to decrease mortality
• may have a positive effect in promoting smoking cessation (controversial)

Disadvantages to screening

• a high false positive rate, requiring interventions, which has the potential to increase screening cost and morbidity on a population level
• ionizing radiation from CT has the potential to increase radiation-induced cancer on a population level
• possible "overdiagnosis" (the cancers found and treated may not effectively decrease the patient's mortality)
• may have a negative effect in promoting smoking cessation (controversial)

Evidence

National lung screening trial

• randomized controlled trial ³
• n = 53,454
• 55-74 years of age
• former or current smokers with over 30 pack-year history
• slightly healthier study cohort than U.S. population overall
• three rounds of annual screening
• positive if at least one noncalcified nodule >= 4 mm
• nodules stable over three screening sessions considered benign
• chest radiograph screening exam used as a control

Results

• low-dose CT detected more nodules than radiograph and greater than twice the diagnosis of stage IA
• ~20% relative reduction in lung cancer mortality in the LDCT arm [95% CI, 6.8-26.7%]
• absolute risk reduction in lung cancer death by 3-4:1000 individuals screened
• ~6.7% reduction in all-cause mortality [95% CI, 1.2-13.6%]
•  overall, 320 screened to save one life (mammography 1:465-601)

As with any screening program, the population-level benefits must be greater than the risks. There is increasing evidence that low-dose lung cancer screening benefits outweigh the risks at this time for selected patient groups. There is continued debate over the cost-effectiveness of screening, but it may be cost-effective if limited to the study population or selected subgroups of the study population.

Further studies will refine lung cancer screening strategy, including a possible volume-based nodule assessment rather than single longest dimension assessment.