Incidence, correlates, and chest radiographic yield of new lung cancer diagnosis in 3398 patients with pneumonia.

Background: One reason chest radiographs are recommended after pneumonia is to exclude underlying lung cancer. Our aims were to determine the incidence and correlates of new lung cancer and the diagnostic yield of new lung cancer by chest radiography in patients with pneumonia.

Methods: We conducted a population-based cohort study of patients with chest radiography-confirmed pneumonia, who were discharged alive from hospitals and emergency departments in Edmonton, Alberta, Canada. Patients were enrolled from 2000 through 2002 and followed up for 5 years. We determined incidence of new lung cancer and receipt of chest radiographs within 90 days, 1 year, and 5 years. Multivariable proportional hazards analyses were used to determine independent correlates of lung cancer.

Results: There were 3398 patients; 59% were 50 years or older, 52% were male, and 17% were smokers. Half (49%) were admitted to hospital. At 90 days, 36 patients (1.1%) had new lung cancer; at 1 year, 57 patients (1.7%); and over 5 years, 79 patients (2.3%). The median time to diagnosis was 109 days (interquartile range, 27-423 days). Characteristics independently associated with lung cancer included age 50 years or older (adjusted hazard ratio [aHR], 19.0; 95% confidence interval [CI], 5.7-63.6), male sex (aHR, 1.8; 95% CI, 1.1-2.9), and smoking (aHR, 1.7; 95% CI, 1.0-3.0). Of the patients, 1354 (40%) had follow-up chest radiographs within 90 days, and the diagnostic yield of lung cancer was 2.5%; if radiographs were restricted to patients 50 years or older, the yield would have been 2.8%.

Conclusions: The incidence of new lung cancer after pneumonia is low: approximately 1% within 90 days and 2% over 5 years. Routine chest radiographs after pneumonia for detecting lung cancer are not warranted, although our study suggests that patients 50 years or older should be targeted for radiographic follow-up.