Background: Viscum album L. extracts (VAE, European mistletoe) are a widely used medicinal plant extract in gynaecological and breast-cancer treatment.

Background: Major surgery suppresses natural killer (NK) cell cytotoxic activity which is potentially harmful for cancer patients by favouring haematogenic tumour cell dissemination. The influence of a perioperative infusion of a standardized mistletoe extract (Iscador ®) on immune functions was tested in a prospective, sequential, randomized clinical trial. Patients and Methods: Colorectal cancer patients undergoing open tumour resection were randomly assigned to either mistletoe infusion or no additional therapy. We hypothesized that mistletoe infusion improves NK cell activity and increases expression of MHC class II antigen HLA-DR on monocytes 24 h and 7 days after surgery, respectively. For statistical analysis we used a sequential study design. The decision boundaries for the two triangular tests were calculated for altogether 62 patients. Results: The sequential study design allowed stopping the recruitment prematurely. NK cell activity differed significantly between the therapy groups 24 h after surgery (p = 0.027). The absolute number of HLA-DR molecules on monocytes did not differ 7 days after surgery. NK cell activity of patients treated with mistletoe extract did not change significantly during the course of the study (-7.9% 24 h after surgery), whereas HLA-DR expression changed significantly (-38.5% at day 7 after surgery). For control patients both parameters decreased significantly after surgery (NK cell activity: -44.4% at 24 h; HLA-DR expression: -32.9% at day 7 after surgery). Conclusion: Perioperative infusion of mistletoe extracts can prevent a suppression of NK cell activity in cancer patients. The impact of this therapy on relapse and survival should be tested in further studies.

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