Surgical stress and anaesthetics are able to suppress the immune system. This may accelerate the growth and metastasis of residual cancer cells. As Viscum album L. extracts (VA-E) are known to exert both effects, immunomodulating and apoptosis-inducing properties, a Good-Clinical-Practice-guided, prospective bi-centric phase II study was conducted to measure the influence of a perioperative intravenous application of a VA-E on granulocyte function. In 98 patients with breast cancer, it was shown that a single intravenous application of the standardized VA-E "Iscador M special" in a final concentration of 1 mg/individual prior to surgery prevented the surgery-associated inhibition of the oxidative burst. As no VA-E-related side-effects were observed, this distinct route of application may be a rationale to restrict immunosuppression by surgical stress and anaesthesia.