Effect of Concomitant Metformin Use on Hematologic Adverse Events in Non-Small-Cell Lung Cancer Patients Undergoing Pemetrexed-Based Chemotherapy: A Study Using a Japanese Claims Database

Pemetrexed is a folate analog inhibitor for the treatment of non-small-cell lung cancer (NSCLC). Prophylactic supplementation with vitamin B₁₂ and folic acid reduces hematotoxicity associated with pemetrexed. Metformin, the antidiabetic agent, has been associated with the potential side effect of vitamin B₁₂ deficiency. This retrospective observational study aimed to evaluate the effect of concomitant metformin use on hematologic adverse events in patients with NSCLC undergoing pemetrexed-based chemotherapy using the Medical Data Vision Database. Patients with stage III or higher NSCLC who received pemetrexed from April 2008 to May 2021 were categorized into metformin-treated (MTF) and non-metformin-treated (non-MTF) groups. The primary outcome was the proportion of granulocyte colony-stimulating factor (G-CSF) administration during cycle (C) 1 to C2 or C2 to C3 of pemetrexed therapy. Propensity score matching (PSM) was used to balance the baseline characteristics between the groups. A total of 1174 patients met the inclusion criteria (54 in MTF and 1120 in non-MTF). After PSM, 52 patients were included in each group. The median metformin dosage in the MTF group was 500 mg/d before and 625 mg/d after PSM. There were no significant differences between the MTF and non-MTF groups in G-CSF administration (15.4 vs. 21.2%, p=0.446). Multivariate logistic regression analysis also showed that metformin use did not significantly affect hematologic toxicity (odds ratio: 1.208, 95% CI: 0.554-2.634). This suggests that the concomitant use of a relatively low dose of metformin is unlikely to significantly increase the risk of hematotoxicity in Japanese patients with NSCLC receiving pemetrexed-based chemotherapy.