Rationale: Triggering receptor expressed on myeloid cells (TREM)-1 is a molecule crucial for the triggering and amplification of inflammatory response and a new biomarker for sepsis. Tumor-associated macrophages and inflammation in the tumor microenvironment are also involved in cancer progression.

Objectives: To determine the role of TREM-1 in tumor-associated macrophage and cancer progression.

Methods: Using ELISA and Western blot, we measured soluble TREM-1 levels in 65 pleural effusions of various etiologies. We evaluated TREM-1–positive cells by immunocytochemistry in malignant pleural effusion and in lung tumor versus adjacent normal tissue in surgical specimens from 68 patients with non–small cell lung cancer (NSCLC). TREM-1 expression was correlated with patient survival. TREM-1 expression in primary isolated peripheral blood macrophages cocultured with lung cancer cell lines was determined by quantitative real-time reverse transcriptase–polymerase chain reaction.

Measurements and Main Results: Soluble TREM-1 and tumor-associated macrophage TREM-1 expression was increased in malignant pleural effusions in patients with NSCLC. Lung cancer cells could directly up-regulate TREM-1 and proinflammatory cytokine (tumor necrosis factor-α, IL-1β) expression in primary isolated peripheral blood macrophages in coculture experiments. Increased TREM-1–positive tumor-associated macrophages in tumor tissue of patients with NSCLC were associated with reduced disease-free (P = 0.011) and overall survival (P = 0.004). Multivariate Cox regression analysis indicated that TREM-1 was an independent predictor of patient survival (hazard ratio, 2.72; 95% confidence interval, 1.33–5.57; P = 0.006).

Conclusions: Cancer cells can directly up-regulate TREM-1 expression in patients' macrophages. TREM-1 expression in tumor-associated macrophages is associated with cancer recurrence and poor survival of patients with NSCLC. TREM-1 and the inflammatory response may play an important role in cancer progression.