Multiple myeloma is difficult to treat because of the heterogeneity of genomic aberrations and responses to treatment. Currently, bone marrow examinations are used for genomic evaluation at diagnosis, at evaluation of minimal residual disease and at relapse. This is an invasive procedure, but it also carries the risk of false negatives due to spatial heterogeneity. Therefore, researchers developed a non-invasive disease monitoring tool using circulating tumor DNA (ctDNA) that could aid in disease management and assess response to CAR T-cell therapy in multiple myeloma patients. The investigators developed a multiple myeloma-specific liquid biopsy panel using personalized cancer profiling by deep sequencing (CAPP-Seq) to quantify ctDNA in plasma, germline, and tumor DNA samples from multiple myeloma patients. The results suggest that ctDNA can better capture the spatial heterogeneity of the tumor. The researchers also applied CAPP-Seq to patients receiving idecabtagene vicleucel and found that those who had a response of at least 90 days had significantly lower levels of ctDNA at day 28 post-infusion than those who experienced early disease progression.