Genomic analysis of BMA samples from MagnetisMM-3 identified an association between higher TNFRSF17 expression in the tumor microenvironment and unfavorable outcomes, likely due to its surrogacy with increased tumor burden. Features of high-risk disease were also associated with lack of response to elranatamab. Adjusting for tumor cell content revealed additional aspects of the tumor microenvironment associated with poor response, including increased myeloid cell populations.