e18302 Background: Findings from few studies examining preferences for MM treatment are limited in application, as they are largely missing the voices of patients (PTs). The present qualitative study elucidates PT preferences, the perceived trade-offs they are willing to make, and how these may differ by line of therapy (LOT). Methods: Semi-structured phone interviews were conducted with MM PTs (front-line [FL] = 11, early relapse 1- 2 prior-lines [1/2PL] = 10) recruited via purposive sampling from targeted panels and PT groups, April-May 2018. A discussion guide was developed and a trained interviewer conducted 1-hour interviews on the diversity and valence of factors influencing how PTs evaluate potential regimens and how preferences vary by experience (i.e., LOT). Interviews were audio recorded and transcribed, responses coded, and content analysis performed to identify key themes emerging from textual data. Results: The sample was 42% male, mean age 64 years, with mean 58 months since diagnosis. Three key themes were identified. Firstly, treatment decision-making, revealed that trust in one’s health care provider (HCP) was a potent influence on treatment choice. Whereas FL PTs reported often only one option is offered and rely on HCP to make decisions, 1/2PL PTs consider other sources of information and engage in more shared decision-making. Secondly, expectations about treatment, illustrated that HCPs discuss important factors, e.g., efficacy and tolerability, in general terms with FL PTs and provide more details to 1/2PL PTs. Lastly, “ top of mind” factors that influenced treatment decisions, effectiveness, followed by side effects, emerged as the greatest influences on preference, although 1/2PL PTs reported less concern with side effects than FL PTs. Relatedly, quality of life was described as salient; the lived experience of treatment was often mentioned within the context of side effects. Conclusions: The way PTs construct, prioritize, and communicate about treatment when assessing “benefit-risk” is a dynamic process, based on where PTs are in their treatment journey. By examining treatment preferences grounded in PTs’ lived and changing experiences with MM, the findings may contribute to better PT-HCP engagement through treatment decision-making and improve clinical care.