KITLG (KIT ligand) is a cytokine that binds to the KIT receptor tyrosine kinase to regulate cell survival, proliferation, and hematopoiesis [UniProt]. The protein activates multiple signaling cascades including PI3K-AKT, RAS-RAF-MAPK, and STAT pathways, while also promoting PLCG1 activation [UniProt]. KITLG is essential for mast cell development and function [UniProt], with elevated expression observed in endometriotic lesions supporting mast cell recruitment and differentiation 1. In breast cancer, progesterone receptor upregulates KITLG to promote mast cell-derived granulin production, which antagonizes TNFα-induced apoptosis in hormone receptor-positive tumors 2. Genetically, KITLG mutations cause Familial Progressive Hyper- and Hypopigmentation and Dyschromatosis universalis hereditaria type 2 34, with certain polymorphisms potentially increasing testicular germ cell tumor susceptibility 5. Epigenetically, KITLG DNA methylation inversely correlates with stress-induced cortisol levels, suggesting a role in stress response regulation 6. In heart failure, KITLG is among the most downregulated proteins in severely congested patients 7. These findings establish KITLG as a pleiotropic cytokine with implications across hematology, oncology, endocrinology, and cardiovascular pathophysiology.