Objective: Although the incidence of peripheral squamous cell carcinomas (SqCCs) of the lung has increased over recent years, histologic prognostic factors for small peripheral SqCCs have not been well established. The aim of this study is to identify clinicopathologic prognostic factors.
Materials and methods: We evaluated various clinicopathologic parameters in 101 patients with peripheral lung SqCCs (defined as tumors located in or more peripheral to the fourth branching bronchus), measuring < or = 30 mm in diameter.
Results: Multivariate analysis showed that the size of the minimal tumor nest (MTN), a background of usual interstitial pneumonia (UIP) and lymph node metastasis were significant prognostic factors. MTN sizes were defined as large (>6 tumor cells), small (2-5 tumor cells) or single cell. The 5-year disease-free survival rate was significantly worse in patients with single cell nests (50 patients, 69.5%) than in those with small nests (42 patients, 94.1%) (P = 0.0035, log rank test). The MTN size had a significant impact on survival in patients with pathologic stage IA disease and tumors < or = 20 mm in diameter. A background of UIP, which correlated with the presence of a single cell invasive component and pleural involvement, was also a poor prognostic factor, suggesting that peripheral SqCC in UIP is highly malignant even if the tumor is small.
Conclusion: The MTN size is a useful prognostic factor for small peripheral SqCCs. Tumors with a single cell invasive component appear to be highly malignant, and should be distinguished from invasive cancers with a low malignant potential (tumors with large or small tumor nest components).