AHCYL1 (adenosylhomocysteinase like 1), also known as IRBIT, is a multifunctional cellular regulator with tissue-dependent roles in cancer and cardiac pathophysiology. Its primary function involves regulating calcium homeostasis through competitive inhibition of the inositol 1,4,5-trisphosphate receptor (IP3R), modulating ER-to-mitochondria calcium transfer 1. In epithelial tissues, AHCYL1 coordinates HCO3⁻ and fluid secretion by controlling IP3R sensitivity and activating ion transporters (CFTR, SLC26A6, SLC4A4) in response to extracellular stimuli 23. In cancer, AHCYL1 exhibits paradoxical roles depending on context. In NRAS-mutated melanoma, AHCYL1 is upregulated and essential for tumor growth by suppressing ER calcium release and preventing unfolded protein response-mediated apoptosis 4. Similarly, in non-small cell lung carcinoma, AHCYL1 enhances PREX2-driven proliferation through regulation of GEF activity 5. However, in lung adenocarcinoma, AHCYL1 acts as a tumor suppressor by inhibiting stemness and tumorigenicity 6, while in ovarian carcinoma AHCYL1 expression predicts favorable prognosis 7. Clinically, AHCYL1 overexpression induces cardiac hypertrophy with impaired systolic function through disrupted calcium signaling 8. AHCYL1 also supports hepatitis C virus propagation through interaction with NS5A protein 9, and serves as a fusion partner in FGFR2 translocations driving intrahepatic cholangiocarcinoma 10.