IntroductionUnresectable, well-differentiated nonfunctioning gastroenteropancreatic neuroendocrine tumors (GEP-NETs) can be monitored (watchful waiting, WW) or treated with systemic therapy such as somatostatin analogues (SSAs) to delay progression. We applied a reflective multicriteria decision analysis (MCDA) shared-decision framework (previously developed for the USA) to explore what matters to Spanish patients and clinicians considering GEP-NET treatment options.MethodsThe EVIDEM-derived framework was updated and adapted to the Spanish context. During a Chatham House session, five patients and six physicians assigned criteria weights using hierarchical point allocation and direct rating scale (alternative analysis). Informed by synthesized evidence embedded in the framework, participants scored how each criterion favored SSA treatment (reference case lanreotide) or WW and shared insights and knowledge. Weights and scores were combined into value contributions (norm. weight × score/5), which were added across criteria to derive the relative benefit–risk balance (RBRB, scale − 1 to + 1). Exploratory comparisons to US study findings were performed.ResultsFocusing on intervention outcomes (effectiveness, patient-reported, and safety), the mean RBRB favored treatment over WW (+ 0.32 ± 0.24), with the largest contributions from progression-free survival (+ 0.11 ± SD 0.07), fatal adverse events (+ 0.06 ± SD 0.08), and impact on HRQoL (+ 0.04 ± SD 0.04). Consideration of modulating criteria (type of benefit, need, costs, evidence, and feasibility) increased the RBRB to + 0.50 ± 0.14, with type of therapeutic benefit (+ 0.10 ± SD 0.08) and quality of evidence (+ 0.08 ± SD 0.06) contributing most towards treatment. Alternative weighting yielded similar results. Results were broadly comparable to those derived from the US study.ConclusionThe multicriteria framework helped Spanish patients and clinicians identify and express what matters to them. The approach is transferable across decision-making contexts.FundingIPSEN Pharma.Electronic supplementary materialThe online version of this article (10.1007/s12325-018-0745-6) contains supplementary material, which is available to authorized users.