Glucose uptake and glycolytic metabolism are enhanced in cancer cells compared to normal cells and tissues. Increased expression of glucose transporter 1 (GLUT1) has been reported in human malignant cells. The aim of this study is to determine the expression of the facilitative glucose transporter protein GLUT1 in human breast carcinomas and a possible correlation between GLUT1 expression and clinical outcome including disease-free or overall survival. One hundred consecutive formalin-fixed, paraffin-embedded sections of invasive breast carcinomas were evaluated by means of immunohistochemical staining of GLUT1. Forty-seven (47%) of 100 breast carcinomas showed positive staining for GLUT1. Expression of GLUT1 correlated significantly with nuclear grade (P < 0.001), estrogen receptor status (P = 0.002), and progesterone receptor status (P = 0.001). The mean disease-free survival periods of GLUT1-positive and -negative patients were 47 +/- 2.4 months and 54.3 +/- 1.3 months, respectively (P = 0.017). The mean overall survival periods of GLUT1-positive and -negative patients were 48.7 +/- 2.2 and 56.1+/- 1.3 months, respectively (P = 0.043). In the multivariate analysis, disease-free survival correlated significantly with GLUT1, tumor size, and lymph node involvement (P = 0.043, P = 0.014, and P = 0.045, respectively). In analysis of overall survival, however, lymph node involvement, tumor size, and nuclear grade were statistically significant (P = 0.024, P = 0.023, and P = 0.003, respectively). Our data suggest that absence of GLUT1 expression significantly increases disease-free survival. These findings demonstrate that GLUT1 expression in breast carcinoma can be a marker of aggressive biological behavior and identifies a worse prognosis in breast carcinoma patients.