PD-166866 is primarily used in research settings to study its effects on cellular processes, particularly in the context of cancer and fibrosis. It functions as a potent inhibitor of fibroblast growth factor receptor (FGFR) signaling, which plays a critical role in cell proliferation, differentiation, and survival. By blocking FGFR activity, PD-166866 helps researchers understand the mechanisms underlying tumor growth and fibrosis development. This compound is valuable in preclinical studies aimed at identifying potential therapeutic targets for diseases driven by abnormal FGFR signaling, such as certain cancers and tissue scarring conditions. Its application extends to in vitro and in vivo experiments, providing insights into the efficacy of FGFR inhibition as a treatment strategy.