Strengthening the foundations of shared decision-making in oncology: Systematic review and formal representation of theoretical models

OBJECTIVES: Shared decision-making (SDM) is central to person-centred care, and particularly critical in oncology. Yet, its clinical implementation remains inconsistent. A strong theoretical foundation is essential for developing and sustaining effective SDM practices. Formal representation of theories enhances clarity and testability, enabling the accumulation of reliable evidence to support implementation. We systematically reviewed SDM models in oncology and formally mapped the constructs proposed, their definitions and operationalization, and the hypothesized relationships among them. METHODS: Peer-reviewed articles describing SDM models in oncology were searched in PubMed, Embase, Web of Science, PsycINFO, CINAHL, and the Cochrane library. Constructs, definitions, and interrelationships were extracted and visualised using an ontology-based modelling system. Study quality was assessed using a modified QuADS tool. Findings were synthesised narratively. RESULTS: Twenty studies were included, spanning diverse methodologies and cancer localisations. A total of 225 constructs were identified. The models varied in focus, terminology, and detail. Nine models focused on the SDM process only, describing diverse sequences of steps using different terms, among which four common steps could be identified: exchange information; discuss alternatives; elicit patient values and preferences; and make a decision. Ten models included SDM determinants at patient-, clinician-, healthcare system- and treatment-level, and interpersonal and social factors. Six models included SDM outcomes such as satisfaction with care, decision or relationship, health and quality of life. Three models specified other components, i.e. SDM actors, goals or assumptions. Ambiguity in construct definitions and interrelationships was common, and several models lacked explicit theoretical propositions. CONCLUSIONS AND PRACTICE IMPLICATIONS: Beyond the commonalities identified across models, the diversity and lack of formal specification of oncology-specific SDM models pose challenges for the development, evaluation and implementation of SDM interventions in practice. Given the theoretical fragmentation and current challenges in SDM implementation, advancing theory remains crucial to inform practice and improve patient outcomes.