Background: Clinical staging, as used for patients treated with stereotactic body radiotherapy (SBRT) for early-stage lung cancer, inadequately accounts for pleural invasion, which is a pathologic criteria. Considering the current situation, we analyzed effects of relationships between tumors and the pleura on treatment outcomes of SBRT for early-stage lung cancer. Materials and methods: Among consecutive patients treated with SBRT between 2006 and 2017, we retrospectively identified non-small cell lung cancer patients with primary tumor diameters ≤4 cm and N0M0. The relationships between tumors and the pleura were investigated. The effects of these findings on treatment outcomes were analyzed. Results: We identified 386 patients which met the inclusion criteria. Among these patients, 323 patients were with tumors of 0.1–3.0 cm (T1-size), and 63 patients were with tumors of 3.1–4.0 cm (T2a-size). Among patients with T1-size tumors, 120, 134, and 23 had findings of pleural contact, pleural indentation, and pleural thickening, respectively. When we divided T1-size patients into 2 groups based on pleural contact (contact− or contact+), the 3-year cause-specific mortality and overall survival in patients with T1-size & contact+ were significantly worse than those in patients with T1-size & contact− (17.6% (95% confidence interval (CI), 10.7–25.9%) vs. 6.6% (95% CI, 3.5–11.1%), p < 0.01), and 58.2% (95% CI, 47.6–67.5%) vs. 77.6% (95% CI, 70.5–83.2%), p < 0.01). Local recurrence, regional recurrence, pleural cavity recurrence, and distant metastasis were associated with worse cause-specific mortality and overall survival. On multivariate analysis, pleural contact was associated with cause-specific mortality (hazard ratio (HR), 1.96; 95% CI, 1.09–3.52; p = 0.03) and overall survival (HR, 1.59; 95% CI, 1.08–2.34; p = 0.02). Conclusion: Pleural contact in clinical T1N0M0 lung cancer patients was associated with significantly worse survivals.
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