AFF4 and leukemia: In addition, our results suggest that inhibition of the SEC by flavopiridol could reduce the sphere-forming ability and proliferating cell number of Lgr5+ progenitors in the differentiation assay, which is consistent with previous reports that AFF1 promotes leukemia cell proliferation (Fioretti et al., 2019), that AFF4 enhances the sphere-forming capacity and tumor-initiation capacity in head and neck squamous cell carcinoma (Deng et al., 2018), and that ELL3 stimulates the proliferation and stem cell properties of breast cancer cells (Ahn et al., 2013).