RBM39 and cancer: To evaluate the functional impact of E7820 on splicing, we collected PB and BM MNCs from patients (Supplementary Table 4) and leukemia cell lines with mutations in SF3B1, SRSF2, and U2AF1 following in vitro treatment with E7820 at doses (1 μM treatment for 24 h) previously identified as achieving >90% RBM39 degradation and having anti-cancer effect (Fig. 1B) [13, 14].