The utility of histological subtype for predicting survival of lung cancer patients with rheumatoid arthritis

BACKGROUND: This study determined whether the survival of lung cancer (LC) patients with rheumatoid arthritis (RA) is differed by histological subtype. MATERIALS: This observational, retrospective study compared the LC survival rate of 34 RA patients with that of 132 age- and sex-matched patients without RA who received medical care from 2011 to 2016. Survival curves were generated using the Kaplan-Meier method. Cox proportional hazards regression analyses were used to estimate hazard ratios and determine risk factors predicting mortality according to histological subtype, including small cell lung cancer (SCLC), and non-small cell lung cancer (NSCLC). RESULTS: The predominant histological subtype was adenocarcinoma in both groups, however, a larger proportion of SCLC patients was noted in patients with both LC and RA, compared to those with LC but without RA (26.5% vs. 12.9%, respectively; P=0.0317). LC patients with RA had a significantly lower body mass index (P=0.0488), and a higher proportion of interstitial lung disease (P<0.0001), compared to patients without RA. There was no statistical difference in the distribution of smoking status, stage, or comorbidity index between groups. Overall survival did not differ between LC patients with and without RA. Mortality was significantly worse for RA patients with SCLC than those with NSCLC (P=0.0404), and RA was associated with a 3.26-fold increase in mortality for SCLC patients with versus without RA (P=0.0350; 95% confidence interval: 1.05–9.56). However, RA was not a risk factor for mortality in NSCLC and, even in histological subtypes including lung adenocarcinoma and squamous cell carcinoma. CONCLUSIONS: RA was not associated with a lower overall survival rate for LC patients, irrespective of histological subtype. Because the effects of RA on LC mortality might differ between SCLC and NSCLC patients, future studies should recognize that the histological subtype may affect the outcome.