PURPOSE:It is still controversial whether a low selenium level and a reduced activity of the selenium‐dependent enzyme, glutathione peroxidase, in blood are associated with an increased risk and poor prognosis of cancer in humans. This study evaluates whether colorectal cancer patients have lower serum selenium and glutathione peroxidase levels than a gender‐matched and age‐matched control group and whether there is a correlation to clinical data and prognosis.METHODS:In a retrospective study, serum selenium and glutathione peroxidase activity of 106 patients with colorectal cancer were determined. Clinical data were provided by our long‐term follow‐up program for colorectal cancer patients.RESULTS:Patients with a selenium level <70 &mgr;g/l had a significantly lower mean survival time and a lower cumulative cancer‐related survival rate than patients with a selenium level >70 &mgr;g/l (P=0.0009). When considering the different tumor stages, a decline of the mean selenium level in the T4 carcinoma group was found in the analysis of variance (P<0.05). The lowest selenium level was found for patients with advanced tumor disease and in a preoperative situation,i.e., high tumor burden. In comparison with the control group, the cancer group showed a significant reduction of serum glutathione peroxidase activity (P<0.01) but no significant difference in selenium level.CONCLUSIONS:These results support the hypothesis of an association between low selenium level and advanced tumor disease. From our data, it cannot be decided whether this phenomenon is more likely to be a consequence or a causative factor for development and course of the disease.