XL139 is used in cancer research and development, particularly for cancers associated with the Hedgehog signaling pathway, which plays a key role in cell growth regulation. Designed to inhibit the Smoothened protein, a component of this pathway, XL139 can slow or halt cancer cell growth. Currently in clinical trials, it is being evaluated for efficacy and safety in treating various cancers, such as pancreatic cancer, basal cell skin carcinoma, and other Hedgehog pathway-related malignancies. These studies aim to develop more effective treatment options for cancer patients in the future.