To assess the effects of usual interstitial pneumonia (UIP) and smoking in rheumatoid arthritis (RA) patients regarding lung cancer risk, we studied 86 RA patients (14 patients with lung cancer, 58 patients with UIP (RA/ UIP), and 14 patients with both). Among the 28 RA patients with lung cancer, 14 patients (50%) had UIP. Compared to the lung cancer patients without UIP, the proportion of smokers (92.6 vs 50%, p = 0.0328) and total pack-years of smoking (57.1 +/- 37.1 vs 19.5 +/- 21.9, p = 0.003) were significantly higher in lung cancer patients with UIP. There was no significant difference in age, sex, and histological type and location of lung cancer between these two groups. Among the 72 RA/UIP patients, 14 patients (19.4%) had lung cancer. Compared to RA/UIP-only patients, the proportion of smokers (92.6 vs 46.6%, p = 0.002) and total pack-years of smoking (57.1 +/- 37.1 vs 25.4 37.4, p = 0.006) were significantly higher in RA/UIP patients with lung cancer. There was no significant difference in age, sex, and the duration of RA between these two groups. The odds ratio of smoking and total pack-years of smoking over 20 for the development of lung cancer in RA/UIP patients were 14.93 and 21.27, and the differences were statistically significant (p = 0.002 and p < 0.001, respectively).
50% of RA patients with lung cancer had RA/UIP and 19.4% of RA/UIP patients had lung cancer. These findings suggest that RA/UIP may be associated with increased risk of development of lung cancer in RA patients. In an RA cohort study to assess the development of lung cancer, RA patients should be divided into two groups, one with RA/UIP and another without RA/UIP. Smokers with RA/UIP should be recommended to cease smoking.