BACKGROUND:
Cancer is among the leading causes of death in Chile, with significant disparities in access to healthcare. While the National Cancer Plan 2020-2028 emphasizes social participation, leaders and members of civil society organizations often lack technical knowledge for effective political incidence. We assessed the effect of a co-designed educational intervention ("Lidera con Ciencia") on improving knowledge.

METHODS:
A quasi-experimental -controlled before-and-after- study was conducted in Chile (2024-2025). Following co-designed workshops prioritizing educational needs, 56 members from cancer-related civil society organizations were allocated to intervention (n=28) or control (n=28) groups. The intervention consisted of 17 hours of hybrid training covering public health, evidence-based medicine, health technology assessment, equity, socio-anthropology of health, and citizen participation. Knowledge was assessed using validated scales (0-30 points). Data were collected before and after the intervention via online surveys, with no participants lost to follow-up. Difference-in-Differences (DiD) analysis using Generalized Estimating Equations quantified intervention effects, adjusting for age, gender, and region. An additional qualitative component using focus groups explored participants' experiences immediately and three months post-intervention. The study had ethics approval and considered informed consents. Study funded by the Center for Cancer Prevention and Control (FONDAP 152220002, ANID-Chilean Government).

RESULTS:
DiD analysis revealed significant 10.5% improvement in overall knowledge scores attributable to the intervention (CoeffB=0.099,p=0.029). Subset analysis showed significant gains specifically in evidence-based medicine knowledge (CoeffB=2.47,p=0.07). Qualitative findings highlighted substantial perceived learning gains, increased confidence, empowerment, and successful application of knowledge in health decision-making spaces. Participants reported forming strategic alliances, establishing formal organizations, and effectively advocating in policy meetings.

CONCLUSIONS:
Co-designed educational interventions can significantly enhance technical knowledge and perceived confidence among cancer organization members. These findings support institutionalizing participatory capacity-building initiatives to strengthen democratic engagement in health governance and HTA processes, promoting equity and legitimacy in health decision-making in Chile and similar contexts.