Lung carcinoma is often associated with interstitial lung disease (ILD), and the prognosis of lung cancer accompanied by ILD is unfavorable. In this study, cases of patients with primary lung cancer with or without ILD were reviewed to analyze surgical outcome, with special interest in the conformity of clinical and pathologic stages, pathologic findings of pleural invasion, malignant pleurisy first detected at the time of thoracotomy, and survival.

Retrospective chart review was performed for 1,264 primary lung cancer patients who underwent surgery from 2004 to 2015. Concomitant ILD was diagnosed by pathological examination or preoperative chest computed tomography findings.

ILD was found in 104 patients (8.2%) with primary lung cancer. Conformity of clinical and pathological stages in the ILD-positive patients was poor, with a lower kappa value than that for the 1,160 ILD-negative patients (0.34 versus 0.51). The ILD group had significantly higher incidences of pleural invasion and unexpected malignant pleurisy than did the non-ILD group (for pleural invasion, 49.0% versus 24.5%, p < 0.0001; for malignant pleurisy, 7.69% versus 1.47%, p < 0.0001). The 5-year overall survival rates of the ILD group showed significantly lower than those of the non-ILD group (45.2% versus 70.1%; p = 0.0014) after propensity score matching.

In lung cancer, the concomitant existence of ILD is a risk factor for pleural invasion. Concomitant ILD might cause underestimation of clinical staging, increase the chance of unexpected malignant pleurisy during surgery, and shorten survival time.