STAT3 and B-cell chronic lymphocytic leukemia: It is known that phosphorylation of STAT3 on S727 is a signature of CLL development (Hazan-Halevy et al., 2010), as it can regulate the transcription function of the STAT3, and is associated with mitochondrial localization of STAT3 in CLL patients’ cells (Brachet-Botineau et al., 2020).