Used in targeted therapy for non-small cell lung cancer (NSCLC) with EGFR mutations, particularly effective against T790M resistance mutation. It selectively inhibits mutant forms of EGFR while sparing wild-type, reducing side effects. Commonly prescribed for patients who progressed on first-line EGFR inhibitors. Administered orally, it shows good central nervous system penetration, making it useful in treating brain metastases. Its use is guided by genetic testing to confirm EGFR mutation status.