EGFR and Skin rash: Afatinib is reported to be ineffective against lung cancer harboring EGFR T790M positive mutations, because concentrations at which afatinib inhibits lung cancer cells harboring EGFR T790M are not achievable in humans due to dose limiting toxicities such as skin rash and diarrhea, indicating a narrow therapeutic window of afatinib for EGFR T790M [40].