Volume doubling time of lung cancer detected in idiopathic interstitial pneumonia: comparison with that in chronic obstructive pulmonary disease.

OBJECTIVES: To assess the volume doubling time (VDT) of lung cancers in IIP compared with COPD.

METHODS: A total of 61 patients (32 with IIP and 29 with COPD) were identified. A radiologist performed three-dimensional manual segmentation for lung cancers. VDTs were calculated and compared between two groups. Logistic regression was performed to identify factors associated with rapid tumour growth (VDT < 90 days).

RESULTS: The median VDT of lung cancers in IIP (78.2 days) was significantly shorter than that in COPD (126.1 days; p=0.004). Squamous cell carcinoma (SqCC) was the most frequent subtype, followed by small cell lung cancer (SCLC) in IIP. In COPD, SqCC was the most frequent subtype, followed by adenocarcinoma. Rapid tumour growth was observed in 20 cancers from IIP, and in nine cancers from COPD (p=0.021). SCLC was significantly correlated with rapid tumour growth (p=0.038). Multivariate analysis revealed that the presence of IIP was the single independent predictor of rapid tumour growth (p = 0.016; odds ratio, 3.7).

CONCLUSIONS: Lung cancers in IIP showed more rapid growth, with median VDT < 90 days. Therefore, a shorter follow-up interval (<90 days) may be necessary when CT surveillance is considered in IIP patients with suspected lung cancer.

KEY POINTS: • The median VDTs of lung cancers in IIP was 78.2 days. • Rapid tumour growth occurred more frequently in IIP than in COPD. • IIP was the single independent predictor of rapid tumour growth. • Shorter CT follow-up interval may be necessary in IIP with suspicious nodules.