ABSTRACT This application is being submitted in response to the Notice of Special Interest (NOSI) identified as NOT-CA-21-026. Cancer stigma presents a key barrier to cancer control and prevention efforts globally, but especially in low- and middle-income countries (LMICs) and among populations who are at high risk for cancer such as people living with HIV/AIDS (PLWH) and those who smoke. Cancer and cancer stigma’s disproportionate impact on people in LMICs and PLWH warrants intervention to reduce cancer stigma and increase engagement in cancer prevention and care for PLWH living in LMICs; however, little to no research has investigated the unique aspects of cancer stigma among PLWH in an LMIC. In this supplemental study, which is integrated into a three-arm tobacco cessation implementation-effectiveness randomized control trial among PLWH in Viet Nam, we propose to develop a multi-component cancer stigma scale for use among PLWH in an LMIC context. First, a qualitative investigation will be conducted to understand how cancer stigma—and specifically lung cancer stigma—manifests among two groups of PLWH at differentially augmented risks of cancer: PLWH who smoke and PLWH who do not smoke. In this investigation, three theorized components of cancer stigma (i.e., public, internalized, and enacted stigma) and related concepts such as cancer awareness, intersecting stigmas such as HIV stigma and smoking stigma, and salient cultural considerations will be explored. Findings from this qualitative work and cognitive interviewing will inform the selection of items to create a multi-component cancer stigma scale that can be used among PLWH in Viet Nam. The draft scale will be piloted among a sample of Vietnamese PLWH (N=100; n=50 PLWH who smoke and n=50 PLWH who do not smoke). Pilot data will be used to conduct psychometric evaluation of the multi- component cancer stigma scale and explore correlations and associations between cancer stigma, cancer awareness, HIV and smoking stigma, and various related psychosocial and behavioral factors such as harmful psychological symptoms (e.g., depression, anxiety), timing of health-seeking, HIV treatment adherence, smoking cessation, cancer knowledge, and self-efficacy. Developing and validating a multi-component cancer stigma scale in the context of Viet Nam in a way that accounts for culturally salient expressions of stigma is a crucial step towards better understanding and addressing cancer stigma to promote cancer control and prevention across diverse LMIC and low-resource settings.