Importance Guideline recommendations do not necessarily translate into changes in clinical practice behaviour or better patient outcomes. Objective This systematic review aims to identify recent clinical guideline implementation strategies in oncology and to determine their effect primarily on patient-relevant outcomes and secondarily on healthcare professionals' adherence. Methods A systematic search of five electronic databases (PubMed, Web of Science, GIN, CENTRAL, CINAHL) was conducted on 16 december 2022. Randomized controlled trials (RCTs) and non-randomized studies of interventions (NRSIs) assessing the effectiveness of guideline implementation strategies on patient-relevant outcomes (overall survival, quality of life, adverse events) and healthcare professionals' adherence outcomes (screening, referral, prescribing, attitudes, knowledge) in the oncological setting were targeted. The Cochrane risk-of-bias tool and the ROBINS-I tool were used for assessing the risk of bias. Certainty in the evidence was evaluated according to GRADE recommendations. This review was prospectively registered in the International Prospective Register of Systematic Reviews (PROSPERO) with the identification number CRD42021268593. Findings Of 1326 records identified, nine studies, five cluster RCTs and four controlled before-and after studies, were included in the narrative synthesis. All nine studies assess the effect of multi-component interventions in 3577 cancer patients and more than 450 oncologists, nurses and medical staff. Patient-level Educational meetings combined with materials, opinion leaders, audit and feedback, a tailored intervention or academic detailing may have little to no effect on overall survival, quality of life and adverse events of cancer patients compared to no intervention, however, the evidence is either uncertain or very uncertain. Provider-level Multi-component interventions may increase or slightly increase guideline adherence regarding screening, referral and prescribing behaviour of healthcare professionals according to guidelines, but the certainty in evidence is low. The interventions may have little to no effect on attitudes and knowledge of healthcare professionals, still, the evidence is very uncertain. Conclusions and relevance Knowledge and skill accumulation through team-oriented or online educational training and dissemination of materials embedded in multi-component interventions seem to be the most frequently researched guideline implementation strategies in oncology recently. This systematic review provides an overview of recent guideline implementation strategies in oncology, encourages future implementation research in this area and informs policymakers and professional organisations on the development and adoption of implementation strategies.

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