STK17B is a serine/threonine kinase belonging to the death-associated protein kinase family that regulates multiple cellular processes with significant disease implications. Primary function: STK17B phosphorylates myosin light chains and acts as a positive regulator of apoptosis 1. Mechanistically, STK17B suppresses ferroptosis in multiple myeloma by phosphorylating iron-responsive element binding protein 2 (IREB2) at S157 and heat shock protein family B member 1 (HSPB1) at S15, thereby modulating iron homeostasis and ferroptosis suppressors 1. STK17B also sets the threshold for T cell activation through phosphorylation of myosin light chain 2 at Ser19 2. Disease relevance: Elevated STK17B expression correlates with poor outcomes in multiple myeloma and hepatocellular carcinoma, where it promotes epithelial-mesenchymal transition via the AKT/GSK-3β/Snail pathway 13. Conversely, low STK17B expression associates with poor survival in skin cutaneous melanoma, suggesting context-dependent roles 4. Clinical significance: STK17B inhibition enhances ferroptosis and sensitizes myeloma cells to conventional therapies 1, while STK17B inhibition also enhances T cell activation and synergizes with anti-PD-L1 checkpoint blockade 2. High-quality chemical probes enable further functional characterization of this previously understudied kinase 5.