Lung cancer remains the leading cause of cancer-related mortality worldwide, with most patients not surviving beyond a year following their initial diagnosis. The 5-year survival rate is around 17.8 % (Kratzer et al., 2024). Non-small cell lung cancer (NSCLC) is the most prevalent histological type, accounting for about 80 % of lung cancer, and includes subtypes such as adenocarcinoma (Sung et al., 2021; Travis et al., 2015). Approximately half of NSCLC cases are diagnosed at advanced stages, often leading to poor treatment outcomes. These poor outcomes in NSCLC patients are primarily due to metastasis and the subsequent development of chemoresistance (Min and Lee, 2021). These issues limit the effectiveness of conventional therapies, such as chemotherapy and radiation. Furthermore, extensive research is being conducted to overcome drug resistance in NSCLC therapy (Zhang et al., 2019).

The epidermal growth factor receptor (EGFR) is frequently altered or overexpressed in approximately 15–20 % of patients with NSCLC (Hirsch et al., 2017; Mendelsohn and Baselga, 2000; Ray et al., 2009), establishing it as a pivotal target for first-line therapies, particularly through small-molecule tyrosine kinase inhibitors (TKIs). First- and second-generation EGFR TKIs, such as gefitinib and erlotinib, have demonstrated significant antitumor effects and survival benefits in patients with specific EGFR-activating mutations, including L858R and Ex19del (Fukuoka et al., 2011; Maemondo et al., 2010; Mitsudomi et al., 2010). However, most NSCLC patients ultimately experience disease progression due to acquired resistance mechanisms, with the T790M mutation in EGFR being particularly notable (Kosaka et al., 2006; Kwak et al., 2005). Osimertinib (AZD9291), a third-generation EGFR TKI, was designed to address this issue and targets both sensitizing EGFR mutations and the T790M resistance mutation, thus offering a therapeutic option for patients who have progressed after first- or second-generation EGFR TKIs (Greig, 2016; Jänne et al., 2015). Osimertinib exerts its effect by covalently binding to cysteine 797 in the EGFR kinase ATP site, forming irreversible bonds (Wang et al., 2016b; Ward et al., 2013). Compared to previous EGFR inhibitors, osimertinib exhibits significantly reduced activity against wild-type EGFR, yet it maintains robust clinical effectiveness (Cross et al., 2014). Unfortunately, resistance to osimertinib eventually develops in most patients, underscoring a significant limitation due to the absence of effective treatment post-osimertinib resistance (Leonetti et al., 2019).

Macroautophagy, commonly referred to as autophagy, is a cellular mechanism that transports protein aggregates and damaged organelles to lysosomes for degradation, involving encapsulation within double-membrane vesicles (Klionsky and Emr, 2000). Autophagy exhibits a dual nature, functioning as either a pro-survival or pro-death mechanism depending on cellular stress (Ma et al., 2014; White, 2015). During the early stage of carcinogenesis or under chronic tissue damage, autophagy may act as a tumor suppressor by preventing the accumulation of damaged cellular components. however, autophagy can support tumor progression in established tumors by providing metabolic substrates that help cancer cells survive under conditions such as hypoxia, nutrient deprivation, and therapeutic stress (Sun et al., 2013). Various oncogenic signaling pathways, involving EGFR, KRAS, and p53, can modulate autophagic activity, influencing the survival and proliferation of cancer cells (Alves et al., 2015; Henson et al., 2017; Rahman et al., 2022). Autophagy has thus emerged as a critical regulator of both tumor progression and therapeutic response in lung cancer.

Previous studies have demonstrated that EGFR TKIs can induce autophagy in various cancer types (Han et al., 2011; Kang et al., 2017; Shingu et al., 2009). In most cases, this induced autophagy serves a cytoprotective role, enabling cancer cells to evade therapeutic effects. interestingly, in certain cancer cells, the effect of autophagy is context-dependent, acting as either pro-survival or pro-death depending on cellular phenotype (Yun et al., 2020). Given this complexity, autophagy is now widely recognized as a key factor in drug resistance across multiple cancer types, including lung cancer (Auberger and Puissant, 2017; Bellio and Villanueva, 2020; Liao et al., 2019). The dynamic interplay between autophagy and tumor progression highlights the importance of understanding how autophagy is regulated within the tumor microenvironment.

We aimed to elucidate the molecular differences in the action of osimertinib between NSCLCs harboring EGFR-activating mutations, where osimertinib exhibits effective action, and EGFR-wild type NSCLCs, where the drug does not demonstrate efficacy. In PC9 cells, osimertinib-induced cell death is accompanied by the induction of autophagic flux. However, in A549 cells, neither autophagic flux nor cell death occurred, suggesting autophagy is essential for the action of osimertinib. When autophagy was stimulated in PC9/OR cells, which had developed resistance to osimertinib, the resistance was overcome, leading to cell death induced by osimertinib. This suggests that modulating autophagy can overcome acquired resistance to EGFR-TKIs. These findings could be actively utilized to improve effective osimertinib treatment strategies for NSCLC patients.