STAT5A and neoplasm: Additionally, another study has elucidated that STAT5 could also act as a tumour suppressor by upregulating the expression of NADPH oxidase 4 (NOX4), an enzyme involved in the generation of reactive oxygen species (ROS), as well as that of the p53 upregulated modulator of apoptosis (PUMA) and the Bcl-2-interacting mediator of cell death (BIM), which are pro-apoptotic proteins [76].