Minimal Residual Disease in Gastric Cancer: Evidence of an Independent Prognostic Relevance of Urokinase Receptor Expression by Disseminated Tumor Cells in the Bone Marrow

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Abstract
PURPOSE: To study the invasion-related molecule urokinase-type plasminogen activator receptor (u-PAR) expressed by disseminated tumor cells as a biologic predictor of poor survival in a large prospective series of patients with gastric cancer. PATIENTS AND METHODS: In 156 gastric cancer patients (prospective series), disseminated tumor cells in the bone marrow and the u-PAR expressed by these tumor cells were determined by cytokeratin (CK) 18 immunocytochemistry and u-PAR/CK18 double immunocytochemistry. RESULTS: In contrast to the mere detection of disseminated tumor cells at primary surgery, the additional evidence of u-PAR on these cells correlated significantly with pathologic T stage (P = .0474) and the expression of u-PAR (P = .0093) and plasminogen-activator inhibitor 1 (P = .0145) in the primary tumor (immunohistochemistry, χ2). Kaplan-Meier analysis revealed no association with prognosis for the mere detection of disseminated tumor cells. In contrast, a significant association was seen between detection of u-PAR on these cells and shorter disease-free (P < .0001) and overall survival (P < .0001). Multivariate analysis revealed that u-PAR on disseminated tumor cells at the time of primary surgery is an independent prognostic factor for disease-free (95% confidence interval [CI], 1.72 to 3.21; P = .024) and overall survival (P = .0049; relative risk, 2.89; 95% CI, 1.92 to 4.30). CONCLUSION: This is the first large study to show that u-PAR, detected on disseminated tumor cells in the bone marrow, is an independent prognostic parameter in gastric cancer, in contrast to the mere detection of minimal residual disease (MRD). u-PAR may be a promising marker to define a critical subpopulation of disseminated tumor cells and a target to eliminate MRD. Molecular phenotyping of MRD is critical for defining its individual clinical relevance.

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