XL888 is a potent inhibitor of heat shock protein 90 (Hsp90), a molecular chaperone involved in the stabilization and function of various client proteins that are critical in cancer cell survival and proliferation. By inhibiting Hsp90, XL888 promotes the degradation of these client proteins, many of which are oncogenic drivers in various tumor types. This mechanism makes XL888 a valuable candidate in oncology research, particularly for cancers that rely on Hsp90-dependent signaling pathways, such as HER2-positive breast cancer, non-small cell lung cancer, and melanoma. It has been studied for its ability to overcome resistance to targeted therapies, including EGFR and BRAF inhibitors, by simultaneously disrupting multiple downstream signaling pathways. Due to its broad impact on oncoproteins, XL888 is also being explored in combination therapies to enhance antitumor efficacy and prevent disease progression. Its application remains primarily in preclinical and experimental settings, supporting drug development and mechanistic studies in cancer biology.