This is a protocol for a Cochrane Review (intervention). The objectives are as follows:

To assess the effects of mistletoe extracts (Viscum album, European mistletoe) as antitumour treatment and for supportive/palliative care in adults with cancer. We will assess whether mistletoe extracts administered alone or in combination with tumour-specific therapies prolong progression free-intervals (PFI) and/or overall survival (OS); enhance tumour response; alleviate treatment-related adverse effects from conventional cancer treatment e.g. chemo‐ or radiotherapy; improve patient-reported outcomes including health-related QOL; and whether mistletoe extracts produce adverse effects.