Evaluation of concomitant medications
A concomitant medication was defined as any therapeutic drug used to manage a comorbid condition in addition to NSCLC between the last visit and day 1 of EGFR-TKI treatment. All medications administered to every patient at EGFR-TKI treatment initiation were reviewed. Oral, injection (e.g., intravenous, intramuscular, and subcutaneous), suppository, and inhalant medications were included, while as-needed and topical medications were excluded. PP was defined as five or more concomitant medications. For compounding agents, we counted each ingredient separately. PIM use was measured using STOPP ver. 2 criteria,[7] a screening tool for detecting potentially inappropriate prescribing in the elderly (age >= 65 years). In addition to PIM-STOPP v2, we checked PIM use related to EGFR-TKI treatment (PIM-TKI). PIM-TKI was defined as the use of one of the following: (1) concomitant use of cytochrome P450 3A4 (CYP3A4) inhibitors/inducers with gefitinib, erlotinib, or osimertinib[30-32]; (2) concomitant use of CYP1A2 inhibitors with erlotinib[32]; (3) concomitant use of medications affecting the gastric potential of hydrogen (pH), such as antacids with gefitinib or erlotinib[30, 32]; and (4) concomitant use of P-glycoprotein (P-gp) inhibitors/inducers with afatinib[33].