Osteosarcoma (OS),the most common malignant bone tumor with high metastatic potential,frequently affects children and adolescents.Epidermal growth factor receptor (EGFR)-targeted tyrosine kinase inhibitors exhibit encouraging anti-tumor activity for patients with solid tumors,whereas their effects on OS remain controversial.In the present study,we aimed to elucidate the anti-tumor activity of gefitinib for OS,as well as to explore the underlying mechanisms.Gefi-tinib inhibits cell viability,tumor growth,cell migration,and invasion and promotes cell apoptosis and G1 cycle arrest in OS at a relatively high concentration via suppressing the PI3K/Akt and ERK pathways.However,gefitinib treatment results in the feedback activation of signal transducer and activator of transcription 3 (STAT3) induced by interleukin 6 (IL-6) secretion.Combined treat-ment with gefitinib and stattic,an inhibitor for STAT3 phosphorylation,engenders more evident inhibitory effects on cell proliferation,migration,and invasion and promotive effects on cell apop-tosis and G1 phase arrest in OS,compared with the single exposure to gefitinib or stattic.Western blot analysis demonstrates that stattic treatment in gefitinib-treated OS abrogates the IL-6-induced STAT3 activation and subsequently further restrains the activities of EGFR,Akt,and ERK pathways in tumor cells.This study confirms that the EGFR inhibitor of gefitinib has moderate anti-tumor effects on OS through IL-6 secretion-mediated STAT3 activation.Additional administration of stattic in EGFR-targeted therapies may contribute to improve the efficacy for OS.