STAT3 and B-cell chronic lymphocytic leukemia: High levels of expression of miR-21, which was found to function as an oncogene, have been observed in hematological malignancies such as AML, CLL, and glioblastoma, and in many cancer types of solid tumors such as prostate and thus, miR-21 is transcriptionally activated by Stat3 in the IL-6 signaling pathway [35].