FIIN-2 is a potent and irreversible inhibitor of the fibroblast growth factor receptor (FGFR) family, particularly FGFR1–4. It is widely used in cancer research due to its ability to block FGFR signaling pathways that are often dysregulated in tumors. This compound shows strong activity against cancer cell lines harboring FGFR amplifications or mutations, making it a valuable tool for studying targeted therapies in cancers such as bladder, lung, and breast carcinomas. Its irreversible binding mechanism allows for sustained inhibition of FGFR phosphorylation, leading to reduced cell proliferation and induction of apoptosis in FGFR-dependent cancer cells. FIIN-2 is also used to overcome resistance to ATP-competitive FGFR inhibitors, as it targets a cysteine residue outside the ATP-binding pocket, offering a strategic advantage in drug resistance studies. In preclinical research, FIIN-2 helps validate FGFR as a therapeutic target and supports the development of next-generation kinase inhibitors with improved selectivity and efficacy.