Single-cell ATACseq data from patients with RRMM reveal a novel mechanism of tumor suppressor inactivation. (A) Patient RRMM21 showed postgain deletion selected between 2 distinct time points (T1, the earliest; T2, the latest), which led to downregulation of 2 tumor suppressors, namely CTNND1 and MALAT1 (ie, loss of function). (B-C) Single-cell ATAC sequencing showed loss of chromatin accessibility after the postgain deletion near both genes between the 2 samples.