The role of IL-21 in hematological malignancies

► We discuss the expression patterns, source of IL-21/IL-21R in healthy cells. ► We discuss the JAK/STAT signal transduction pathways, especially STAT3. ► Expression of IL-21/IL-21R and its effect in hematological malignancies are discussed in individual sections. ► IL-21 regulates proliferation, survival or apoptosis of hematological malignancies, depending on the neoplastic cell type.