Community Learning Ledgers for Cancer Navigation in Small Island Developing States

<jats:p>Importance. Cancer is the second leading cause of death among patients in the Caribbean, where outcomes are associated with delayed clinical navigation to screening, diagnosis, and treatment. Artificial intelligence is increasingly used to guide patients with cancer to care, but whether these systems provide clinically actionable, facility-verified guidance for individuals in this population, and whether governance of the system is associated with the quality of that guidance, has not been evaluated. Objective. We tested whether a governed community learning platform navigates Caribbean cancer patients better than four ungoverned AI systems, and we tracked how community intelligence accumulates over time. Design, Setting, and Participants. We deployed a community learning ledger (CaribChat.ai) across ten Caribbean jurisdictions beginning March 2, 2026, and report all sessions through June 1, 2026 (N=207). An initial actively-promoted accrual period (March 2 - April 6, 2026; 168 sessions) was followed by continued organic use after active clinical promotion ceased. We then submitted the same 28 patient screening queries to ChatGPT (GPT-4o), Claude Haiku 4.5, DeepSeek-Chat, and OpenEvidence on April 5-6, 2026. Claude Haiku 4.5 powers CaribChat; testing it without governance isolates the governance effect. The platform requires no registration. Exempt under 45 CFR 46.104(d)(4)(ii). Main Outcomes and Measures. We classified 207 community sessions by thematic domain and temporal phase. We scored each of five systems on Caribbean facility citation, actionable navigation, and US-resource leakage across 28 screening queries. Results. The ledger accumulated 207 sessions - 168 during an actively-promoted accrual period (March 2 - April 6) and 39 after active clinical promotion ceased. Community engagement evolved from screening questions to active treatment navigation and diaspora engagement. CaribChat cited verified Caribbean facilities in 28/28 (100%) responses versus 10/28 (35.7%) for ChatGPT and 9/28 (32.1%) for OpenEvidence. CaribChat provided actionable navigation in 28/28 (100%) versus 2/28 (7.1%) for OpenEvidence (P&lt;=.001). The same model scored 100% with governance and 54% without (P&lt;=.001). DeepSeek cited US resources in 57.1% of Caribbean responses. After active clinical promotion ceased, off-codebook queries rose from 2.4% to 26.7% across phases while the governance contract continued to reject every adversarial probe - the community persisted but drifted from the cancer codebook absent clinician curation. The deployment operated within the OECS Health Strategy 2030 and CARICOM regional health frameworks, with queries originating across Caribbean jurisdictions led by Trinidad and Tobago. Conclusions and Relevance. Every ungoverned AI system we tested failed Caribbean cancer navigation. The best scored 68%. The most widely adopted physician platform scored 7%. The same foundation model scored 100% with governance and 54% without. Community intelligence accumulated from the population it serves, not published literature, is what makes health AI work in SIDS. The post-promotion decay shows the requirement is bidirectional: sustained, on-codebook engagement depends on patients and clinicians working together - community participation and active clinical curation are jointly necessary for maximum AI leverage.</jats:p>