BACKGROUND: Breast cancer advocacy movements, driven by advocate-led civil society organizations (CSOs), have proven to be a powerful force for the advancement of cancer control in high-income countries (HICs). However, although patient advocacy movements are growing in low-income and middle-income countries (LMICs) in response to an increasing cancer burden, the experiences and needs of advocate-led breast cancer CSOs in LMICs is understudied. METHODS: The authors conducted a qualitative study using in-depth interviews and focus group discussions with 98 participants representing 23 LMICs in Eastern Europe, Central Asia, East and Southern Africa, and Latin America. RESULTS: Despite geographic, cultural, and socioeconomic differences, the common themes that emerged from the data across the 3 regions are strikingly similar: trust, knowledge gaps, stigma, sharing experiences, and sustainability. The authors identified common facilitators (training/education, relationship building/networking, third-party facilitators, and communication) and barriers (mistrust, stigma, organizational fragility, difficulty translating HIC strategies) to establishing trust, collaboration, and advancing cancer advocacy efforts. To the authors' knowledge, the current study is the first to describe the role that coalitions and regional networks play in advancing breast cancer advocacy in LMICs across multiple regions. CONCLUSIONS: The findings of the current study corroborate the importance of investing in 3-way partnerships between CSOs, political leaders, and health experts. When provided with information that is evidence-based and resource appropriate, as well as opportunities to network, advocates are better equipped to achieve their goals. The authors propose that support for CSOs focuses on building trust through increasing opportunities for engagement, disseminating best practices and evidence-based information, and fostering the creation of platforms for partnerships and networks.