Distinct patient clusters defined by differential ex vivo drug sensitivity. Heat map shows ex vivo drug sensitivity (red) or resistance (blue) to a panel of 31 unique drugs or drug combinations (rows) in 37 patients with myeloid neoplasms (columns), including 34 patients with MDS and 3 patients with MDS/MPN. Patients were clustered on the basis of differential ex vivo drug sensitivity when assayed for cytotoxicity and blast viability using hierarchical clustering (Euclidean distance metric, Ward linkage criterion). Cell color indicates normalized blast percentage (z-score transformed) compared with vehicle control. Rows above the heat map indicate relevant clinical and biologic variables and the 3 distinct patient clusters. A higher incidence of ASXL1 mutations (P = .008) and higher IPSS-R scores (P = .02) were observed in cluster 2. IDH, isocitrate dehydrogenase; PARP, poly (ADP ribose) polymerase.