Recommendations on complementary and alternative medicine within S3 guidelines in oncology: systematic quality assessment of underlying methodology

PURPOSE: Complementary and alternative medicine (CAM) is used by about half of all patients with cancer. Guidelines are an important tool to introduce evidence-based medicine into routine cancer care. The aim of our study was to assess methodology of the statements and recommendations concerning CAM. METHODS: A systematic assessment of all S3 guidelines published until November 2018 was done. Methodology of all statements and recommendations concerning CAM which were declared as evidence-based was evaluated with respect to international standards. According to the AMSTAR-2 instrument search strategy including filters, searched databases, restrictions to the research question and description of the included studies were examined. In case of adaptations from other guidelines, all underlying guidelines were examined as well. RESULTS: After examining 212 guidelines, 82 evidence-based statements and recommendations regarding CAM could be identified. Four were derived by adaptation, 78 by a de-novo search. Only 11 of 78 (14%) fulfilled all assessment criteria. In 18 (19%) cases no information on search strategy was attainable in any document affiliated to the guideline, in 35 (45%) cases information on search strategy was superficial and in 54 (78%) cases the referred evidence was not presented in adequate detail. CONCLUSIONS: Concerning CAM statements and recommendations within S3 guidelines quality of evidence processing has several shortcomings. Guideline adaptions often lack transparency and traceability. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00432-020-03238-2) contains supplementary material, which is available to authorized users.