DesMethyl Erlotinib (CP-473420) HCl is primarily used in research and development as a metabolite of Erlotinib, a well-known tyrosine kinase inhibitor. Its applications are focused on studying the pharmacokinetics and metabolic pathways of Erlotinib, particularly in cancer therapy. Researchers utilize this compound to better understand how Erlotinib is processed in the body, which aids in optimizing dosing regimens and minimizing side effects in patients undergoing treatment for non-small cell lung cancer and pancreatic cancer. Additionally, it serves as a reference standard in analytical laboratories for the quantification and identification of Erlotinib metabolites in biological samples, ensuring accurate monitoring of drug levels during clinical studies.