How Cancer Online Support Groups Work, for Whom, and in What Circumstances: Realist Review.

Background: Online support groups (OSGs) offer a convenient way for patients with cancer and survivors of cancer to obtain information and support. However, not all OSGs are helpful, and in some cases, they may increase distress. Overall, there is a lack of clear evidence on the effects of OSGs, along with how and why they work. Objective: This study examined how, for whom, and in what contexts OSGs work for patients with cancer and survivors of cancer. Methods: A realist review of the evidence on cancer OSGs was conducted (12 databases, inception to February 15, 2025). We followed Pawson's steps and the RAMESES (Realist and Meta-Narrative Evidence Syntheses: Evolving Standards) quality standards for realist reviews. The Mixed-Methods Appraisal Tool was used to assess the quality of the evidence. Using a realist logic of analysis, we generated a narrative summary of the findings, context-mechanism-outcome configurations, and a program theory (eg, conceptual framework) to explain how cancer OSGs work. Additionally, we developed evidence-based recommendations for optimizing the effectiveness of OSGs. Results: Of 16,659 papers identified, 168 were included. The evidence was organized into 3 categories, 10 concepts, and 57 context-mechanism-outcome configurations. Cancer OSGs can support patients by providing informational, emotional, appraisal, and altruistic support. This can lead to changes in distress, isolation, empowerment, and self-esteem, through negative and positive appraisals as well as coping efforts. These outcomes, however, depend on user attitudes about OSGs (ie, trustworthy, useful, culturally safe, and easy-to-use), how well the OSG fits their needs (ie, health need, sociodemographic or clinical characteristics, and coping style), and perceptions of control (ie, availability, anonymity, privacy, and autonomy). If an OSG was a good fit for a user's needs, whether they experienced positive outcomes depended on features of the communication technology (ie, modality, response time, and visual social cues), group composition and dynamics (ie, norms, moderation, safety, cohesion, and belonging), and the nature and content of interactions (ie, emotional expression, cognitive processing, and empathetic responses). These factors trigger underlying mechanisms such as feeling understood, accepted, cared for, valued, reassured, informed, and confident, which result in positive outcomes. Conclusions: OSGs can address supportive care needs and improve psychosocial well-being for patients with cancer and survivors of cancer. However, outcomes depend on specific contexts and mechanisms that impact how well OSGs meet patients' needs. To optimize effectiveness of OSGs, we recommend (1) helping to assess fit and address specific needs; (2) demonstrating trustworthiness; (3) enhancing anonymity and control, and protecting privacy; (4) enhancing ease-of-use; (5) supporting connection and belonging; (6) encouraging activity; (7) enhancing the nature of content shared to boost therapeutic effects; and (8) monitoring and adjusting design and management strategies.