The role played by the innate immune system in determining survival from non–small-cell lung cancer (NSCLC) is unclear. The aim of this study was to investigate the prognostic significance of macrophage and mast-cell infiltration in NSCLC.

We used immunohistochemistry to identify tryptase⁺ mast cells and CD68⁺ macrophages in the tumor stroma and tumor islets in 175 patients with surgically resected NSCLC.

Macrophages were detected in both the tumor stroma and islets in all patients. Mast cells were detected in the stroma and islets in 99.4% and 68.5% of patients, respectively. Using multivariate Cox proportional hazards analysis, increasing tumor islet macrophage density (P < .001) and tumor islet/stromal macrophage ratio (P < .001) emerged as favorable independent prognostic indicators. In contrast, increasing stromal macrophage density was an independent predictor of reduced survival (P = .001). The presence of tumor islet mast cells (P = .018) and increasing islet/stromal mast-cell ratio (P = .032) were also favorable independent prognostic indicators. Macrophage islet density showed the strongest effect: 5-year survival was 52.9% in patients with an islet macrophage density greater than the median versus 7.7% when less than the median (P < .0001). In the same groups, respectively, median survival was 2,244 versus 334 days (P < .0001). Patients with a high islet macrophage density but incomplete resection survived markedly longer than patients with a low islet macrophage density but complete resection.

The tumor islet CD68⁺ macrophage density is a powerful independent predictor of survival from surgically resected NSCLC. The biologic explanation for this and its implications for the use of adjunctive treatment requires further study.