LAUSR

and resource allocation decisions. This study aimed to assess the number of US patients with MM by LOT in 2020. Methods: Differential equations were used to develop a five-compartment model: LOT1–LOT5+. Patients in LOT1–LOT4 could die or transition to the next LOT. Patients in LOT5+ could remain in that compartment or die. Each LOT was sub-divided based on stem-cell transplant (SCT) eligibility and treatment type (anti-CD38 therapy or ‘other’; patients may switch treatment with LOT progression). Patient numbers were stratified by age (,65 and $65 years) and cytogenetic risk. Results were aggregated to provide patient numbers by LOT. For ‘other’ treatments, mortality and time to next treatment (TTNT) depended on LOT, SCT, age and cytogenetic risk and were informed from published epidemiological/ real-world studies. Anti-CD38 (i.e. daratumumab) use data were based on relative treatment effects in randomised controlled trials. Anti-CD38 use per LOT was based on 2020 market-research data. Probabilistic and deterministic sensitivity analyses quantified the impact of input data variability. Results: The model predicted an MM prevalence of 128,326 US patients, with 106,176 actively receiving treatment (LOT1: 53.9%; LOT2: 25.8%; LOT3: 10.7%; LOT4: 4.9%; LOT5+: 4.7%). An estimated 69.7% (3511/5034) in LOT5+ (standard deviation=861) had prior exposure to proteasome inhibitors, immunomodulatory agents and/or anti-CD38 antibodies. LOT5+ model results were most sensitive to mortality, TTNT and anti-CD38 use. Conclusions: This novel model predicted the number of patients with MM by LOT with an overall prevalence within a 10% deviation of SEER estimates (140,779 US patients); and provides a framework that can be adapted to other countries and healthcare systems. Funding: GlaxoSmithKline: (213290).