Impact of timing and initial recurrence site on post-recurrence survival in resected non-small cell lung cancer.

INTRODUCTION: High recurrence rate following curative surgery for non-small cell lung cancer (NSCLC) presents a major clinical challenge. Understanding the site and timing of recurrence and their impact on post-recurrence survival (PRS) is important for optimal postoperative surveillance and therapeutic intervention. In this study, we investigated the influence of the time to recurrence (TTR) and initial recurrence site on PRS. MATERIALS AND METHODS: This multicentre prospective cohort study included patients who experienced recurrence after NSCLC resection between 2010 and 2015. The relationship between TTR and initial recurrence site, and their impact on PRS, was further evaluated. The hazard ratio (HR) for PRS was analysed using the Cox proportional hazards model. RESULTS: Among 495 patients, the median TTR was 14 (range, 1-158) months; the mode of recurrence was 11 months. Early recurrence within 6 months was observed in 17 % of patients, and 68 % of patients showed recurrence within 2 years post-surgery. The HR for PRS was the highest in patients with a TTR within 6 months, and a noticeable decline was observed after the first 6 months. The HRs of TTRs beyond 2 years were not significantly different. The liver was a significantly unfavourable prognostic site for metastases (HR 2.2; P = 0.01), and metastases frequently recurred within 6 months after surgery. The timing of brain metastasis did not significantly impact the PRS. CONCLUSION: Earlier recurrence after surgery was associated with shorter PRS. In contrast, recurrences occurring >2 years after surgery do not significantly affect PRS.

Prognostic significance of preoperative creatine kinase in resected thymic epithelial tumors.

Background: The preoperative serum creatine kinase (CK) concentration is a prognostic factor for malignant diseases. We investigated the significance of CK in surgically resected thymic epithelial tumors and the relationship between CK and clinicopathological factors. Methods: We retrospectively evaluated the relationship between preoperative CK levels and prognosis in 120 patients with thymic epithelial tumors who underwent surgical resection at two centers. The cutoff for CK was determined by the standard value in our institution (<62 IU/L for men and <45 IU/L for women). The paravertebral muscle at the Th12 level was used to assess skeletal muscle area to investigate sarcopenia. Results: Eighteen patients (15.0%) were categorized into the low CK group. The CK level was not associated with age, sex, performance status, myasthenia gravis, and pathological findings. Preoperative serum albumin and total cholesterol concentrations were significantly lower in the low CK group than in the normal CK group (both P<0.001). Moreover, the Th12 muscle index was lower in the low CK group (P=0.03), indicating that low CK was related to sarcopenia. Kaplan-Meier curve analysis illustrated that patients in the low CK group had significantly shorter disease-free survival (DFS) and overall survival (OS) than those in the normal CK group (P=0.03 and P=0.002, respectively). Multivariate analysis identified low CK as an independent prognostic factor for DFS (P=0.03) and OS (P=0.005). Conclusions: Preoperative serum CK might reflect the host nutritional status in patients with resected thymic epithelial tumors; therefore, CK could be a biomarker of postoperative prognosis.

Clinical Significance of SIRPα Expression on Tumor-Associated Macrophages in Patients with Lung Squamous Cell Carcinoma.

BACKGROUND: Signal-regulatory protein alpha (SIRPα) is an immune checkpoint molecule expressed on macrophages that functions to inhibit phagocytosis by binding to CD47 expressed on tumor cells. SIRPα has attracted increasing attention as a novel target for cancer immunotherapy; however, the expression and immune function of SIRPα in lung squamous cell carcinoma (LUSC) remain unclear. Therefore, this study aimed to identify the clinical importance of SIRPα expression in LUSC and to explore the factors that elevate SIRPα expression. PATIENTS AND METHODS: Primary LUSC specimens surgically resected from 172 patients underwent immunohistochemical evaluation of the association of SIRPα expression on tumor-associated macrophages with clinicopathological features and clinical outcomes. Furthermore, we analyzed the association of SIRPα expression with tumor-infiltrating lymphocytes and the expression of programmed cell death ligand 1 (PD-L1). In vitro, monocytes were treated with cytokines, and SIRPα protein expression was assessed by flow cytometry. RESULTS: There were no differences in SIRPα expression and clinicopathological factors. High SIRPα expression was significantly associated with PD-L1-positive expression, and high CD8, PD-1, and CD163 expression. The high SIRPα expression group showed significantly shorter recurrence-free survival (RFS) and overall survival (OS). On multivariate analysis, high SIRPα expression was an independent poor prognostic factor for RFS and OS. The expression of SIRPα protein in monocytes was upregulated by treatment with IFNγ. CONCLUSION: Our analysis revealed that high SIRPα expression significantly predicts poor prognosis in patients with surgically resected LUSC.

CD155 Expression in Early-Stage Lung Adenocarcinoma.

BACKGROUND: Cluster of differentiation (CD) 155 is a transmembrane protein that belongs to the nectin-like molecule family, which is widely overexpressed in several types of cancer. However, the clinical significance of CD155 in pathologic stage I lung adenocarcinoma remains poorly understood. METHODS: We analyzed 320 patients diagnosed with pathologic stage I lung adenocarcinoma who underwent surgical treatment at Kyushu University Hospital between 2006 and 2015. The number of tumor cells expressing CD155 was assessed by immunohistochemistry, and patients were categorized into high and low CD155 expression groups. We compared the clinical and pathologic characteristics and clinical outcomes between these groups. RESULTS: Mutation status of the epidermal growth factor receptor gene (EGFR) was determined in 237 patients. A total of 106 patients (33.1%) had EGFR wild-type, and 131 patients (40.9%) had EGFR mutant-type. CD155 expression was classified as high in 77 patients (24.1%) and as low in 243 (75.9%) as low. Multivariate analysis identified pleural invasion and EGFR wild-type as independent predictors of high CD155 expression. The Kaplan-Meier plot demonstrated significantly poorer recurrence-free survival and overall survival in the high CD155 group compared with the low CD155 group. Multivariate analysis showed high CD155 expression was an independent poor prognostic factor for recurrence-free and overall survival. Subgroup analyses revealed that a prognostic difference related to CD155 expression was observed only in patients with EGFR wild-type but not in those with EGFR mutant-type. CONCLUSIONS: Our findings suggest that high expression of CD155 is associated with EGFR wild-type and could serve as a valuable prognostic marker in pathologic stage I lung adenocarcinoma, particularly in cases without EGFR mutation.

Clinical and Prognostic Significance of Glutathione Peroxidase 2 in Lung Adenocarcinoma.

BACKGROUND: Glutathione peroxidase 2 (GPX2) is an antioxidant enzyme with an important role in tumor progression in various cancers. However, the clinical significance of GPX2 in lung adenocarcinoma has not been clarified. METHODS: Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to analyze GPX2 mRNA expression. Then, we conducted immunohistochemistry (IHC) to assess GPX2 expression in specimens acquired from 351 patients with lung adenocarcinoma who underwent surgery at Kyushu University from 2003 to 2012. We investigated the association between GPX2 expression and clinicopathological characteristics and further analyzed the prognostic relevance. RESULTS: qRT-PCR revealed that GPX2 mRNA expression was notably higher in tumor cells than in normal tissues. IHC revealed that high GPX2 expression (n = 175, 49.9%) was significantly correlated with male sex, smoking, advanced pathological stage, and the presence of pleural, lymphatic, and vascular invasion. Patients with high GPX2 expression exhibited significantly shorter recurrence-free survival (RFS) and overall survival. Multivariate analysis identified high GPX2 expression as an independent prognostic factor of RFS. CONCLUSIONS: GPX2 expression was significantly associated with pathological malignancy. It is conceivable that high GPX2 expression reflects tumor malignancy. Therefore, high GPX2 expression is a significant prognostic factor of poor prognosis for completely resected lung adenocarcinoma.

Impact of central nervous system metastasis after complete resection of lung adenocarcinomas harboring common EGFR mutation - A real-world database study in Japan: The CReGYT-01 EGFR study.

OBJECTIVES: To clarify the impact of central nervous system (CNS) metastasis on performance status (PS) at relapse, on subsequent treatment(s), and on survival of patients with lung adenocarcinoma harboring common epidermal growth factor receptor (EGFR) mutation. METHODS: We conducted the multicenter real-world database study for patients with radical resections for lung adenocarcinomas between 2015 and 2018 at 21 centers in Japan. EGFR mutational status was examined at each center. RESULTS: Of 4181 patients enrolled, 1431 underwent complete anatomical resection for lung adenocarcinoma harboring common EGFR mutations. Three-hundred-and-twenty patients experienced disease relapse, and 78 (24%) had CNS metastasis. CNS metastasis was significantly more frequent in patients with conventional adjuvant chemotherapy than those without (30% vs. 20%, P = 0.036). Adjuvant chemotherapy did not significantly improve relapse-free survival at any pathological stage (adjusted hazard ratio for stage IA2-3, IB, and II-III was 1.363, 1.287, and 1.004, respectively). CNS metastasis did not affect PS at relapse. Subsequent treatment, mainly consisting of EGFR-tyrosine kinase inhibitors (TKIs), could be equally given in patients with or without CNS metastasis (96% vs. 94%). Overall survival after relapse was equivalent between patients with and without CNS metastasis. CONCLUSION: The efficacy of conventional adjuvant chemotherapy may be limited in patients with lung adenocarcinoma harboring EGFR mutations. CNS metastasis is likely to be found in practice before deterioration in PS, and may have little negative impact on compliance with subsequent EGFR-TKIs and survival after relapse. In this era of adjuvant TKI therapy, further prospective observational studies are desirable to elucidate the optimal management of CNS metastasis.

Impact of Chronic Obstructive Pulmonary Disease on the Long-term Prognosis of Patients Undergoing Lobectomy for Non-small-cell Lung Cancer: A Propensity Score-matched Analysis.

BACKGROUND/AIM: Recent advances in surgery, such as thoracoscopic surgery, have made it possible to treat patients with chronic obstructive pulmonary disease (COPD) more safely than before. This study evaluated the short- and long-term prognosis of lobectomy in non-small cell lung cancer (NSCLC) patients with COPD. PATIENTS AND METHODS: This retrospective, propensity-matched, cohort analysis was conducted from January 2014 to December 2018. Among 441 patients who underwent lobectomy for NSCLC, 158 (35.8%) had a preoperative diagnosis of COPD. Propensity-matched analysis, incorporating preoperative variables, was used to compare postoperative hospital stay and complications, and long-term prognosis between the groups. RESULTS: Propensity matching estimated 145 patients in each group. There was no difference between the two groups for length of postoperative hospital stay (12 vs. 11 days, p=0.306). Postoperative complications were more frequent in the COPD group (24.1%) than in the non-COPD group (16.6%), but the difference was not significant (p=0.108). The 5-year overall survival rate was 86.2% in the COPD group and 82.1% in the non-COPD group after matching (p=0.580). The corresponding 5-year recurrence-free survival rate was 72.8% in the COPD group and 67.2% in the non-COPD group after matching (p=0.601). CONCLUSION: In case of Global Initiative for Chronic Obstructive Lung Disease (GOLD) I/II classification, COPD did not significantly worsen the prognosis of patients with NSCLC after lobectomy.

Development of artificial intelligence prognostic model for surgically resected non-small cell lung cancer.

There are great expectations for artificial intelligence (AI) in medicine. We aimed to develop an AI prognostic model for surgically resected non-small cell lung cancer (NSCLC). This study enrolled 1049 patients with pathological stage I-IIIA surgically resected NSCLC at Kyushu University. We set 17 clinicopathological factors and 30 preoperative and 22 postoperative blood test results as explanatory variables. Disease-free survival (DFS), overall survival (OS), and cancer-specific survival (CSS) were set as objective variables. The eXtreme Gradient Boosting (XGBoost) was used as the machine learning algorithm. The median age was 69 (23-89) years, and 605 patients (57.7%) were male. The numbers of patients with pathological stage IA, IB, IIA, IIB, and IIIA were 553 (52.7%), 223 (21.4%), 100 (9.5%), 55 (5.3%), and 118 (11.2%), respectively. The 5-year DFS, OS, and CSS rates were 71.0%, 82.8%, and 88.7%, respectively. Our AI prognostic model showed that the areas under the curve of the receiver operating characteristic curves of DFS, OS, and CSS at 5 years were 0.890, 0.926, and 0.960, respectively. The AI prognostic model using XGBoost showed good prediction accuracy and provided accurate predictive probability of postoperative prognosis of NSCLC.

Granzyme B (GZMB)-Positive Tumor-Infiltrating Lymphocytes in Lung Adenocarcinoma: Significance as a Prognostic Factor and Association with Immunosuppressive Proteins.

BACKGROUND: Granzyme B (GZMB) is a serine protease produced by cytotoxic lymphocytes that reflects the activity of anti-tumor immune responses in tumor-infiltrating lymphocytes (TILs); however, the prognostic significance of GZMB+ TILs in lung adenocarcinoma is poorly understood. METHODS: We analyzed 273 patients with pathological stage (pStage) I-IIIA lung adenocarcinoma who underwent surgery at Kyushu University from 2003 to 2012. We evaluated GZMB+ TIL counts by immunohistochemistry. We set the cut-off values at 12 cells/0.04 mm2 for GZMB+ TILs and divided the patients into GZMB-High (n = 171) and GZMB-Low (n = 102) groups. Then, we compared the clinicopathological characteristics of the two groups and clinical outcomes. Programmed cell death ligand-1 (PD-L1) and indoleamine 2,3-dioxygenase 1 (IDO1) expression in tumor cells was also evaluated, and combined prognostic analyses of GZMB+ TILs with PD-L1 or IDO1 were performed. RESULTS: GZMB-Low was significantly associated with pStage II-III, PD-L1 positivity, and IDO1 positivity. Disease-free survival (DFS) and overall survival (OS) in the GZMB-Low group were significantly worse than in the GZMB-High group. In multivariable analysis, GZMB-Low was an independent prognostic factor for both DFS and OS. Furthermore, combined prognostic analyses of GZMB+ TILs with PD-L1 or IDO1 showed that GZMB-Low with high expression of these immunosuppressive proteins had the worst prognosis. CONCLUSIONS: We analyzed GZMB+ TIL counts in lung adenocarcinoma and elucidated its prognostic significance and association with PD-L1 and IDO1. GZMB+ TIL counts might reflect the patient's immunity against cancer cells and could be a useful prognostic marker of lung adenocarcinoma.

Impact of the pretreatment prognostic nutritional index on the survival after first-line immunotherapy in non-small-cell lung cancer patients.

BACKGROUND: Immunotherapy has become a standard-of-care for patients with non-small-cell lung cancer (NSCLC). Although several biomarkers, such as programmed cell death-1, have been shown to be useful in selecting patients likely to benefit from immune checkpoint inhibitors (ICIs), more useful and reliable ones should be investigated. The prognostic nutritional index (PNI) is a marker of the immune and nutritional status of the host, and is derived from serum albumin level and peripheral lymphocyte count. Although several groups reported its prognostic role in patients with NSCLC receiving a single ICI, there exist no reports which have demonstrated its role in the first-line ICI combined with or without chemotherapy. MATERIALS AND METHODS: Two-hundred and eighteen patients with NSCLC were included in the current study and received pembrolizumab alone or chemoimmunotherapy as the first-line therapy. Cutoff value of the pretreatment PNI was set as 42.17. RESULTS: Among 218 patients, 123 (56.4%) had a high PNI (≥42.17), while 95 (43.6%) had a low PNI (<42.17). A significant association was observed between the PNI and both the progression-free survival (PFS; hazard ratio [HR] = 0.67, 95% confidence interval [CI]: 0.51-0.88, p = 0.0021) and overall survival (OS; HR = 0.46, 95% CI: 0.32-0.67, p < 0.0001) in the entire population, respectively. The multivariate analysis identified the pretreatment PNI as an independent prognosticator for the PFS (p = 0.0011) and OS (p < 0.0001), and in patients receiving either pembrolizumab alone or chemoimmunotherapy, the pretreatment PNI remained an independent prognostic factor for the OS (p = 0.0270 and 0.0006, respectively). CONCLUSION: The PNI might help clinicians appropriately identifying patients with better treatment outcomes when receiving first-line ICI therapy.

Prognostic impact of noninvasive areas in resected pathological stage IA lung adenocarcinoma.

MAIN PROBLEMS: In non-small-cell lung cancer, ground-glass opacity on computed tomography imaging reflects pathological noninvasiveness and is a favorable prognostic factor. However, the significance of pathological noninvasive areas (NIAs) has not been fully revealed. In this study, we aimed to elucidate the prognostic impact of NIAs on lung adenocarcinoma. METHODS: We analyzed 402 patients with pathological stage (p-Stage) IA lung adenocarcinoma who underwent surgery in 2013-2016 at two institutions and examined the association of the presence of NIAs with clinicopathological factors and prognosis. Furthermore, after using propensity-score matching to adjust for clinicopathological factors, such as age, sex, smoking history, pathological invasive area size, pathological T factor (p-T), p-Stage, and histological subtype (lepidic predominant adenocarcinoma [LPA] or non-LPA), the prognostic impact of NIAs was evaluated. RESULTS: Patients were divided into NIA-present (N = 231) and NIA-absent (N = 171) groups. Multivariable analysis showed that NIA-present was strongly associated with earlier p-T, earlier p-Stage, LPA, and epidermal growth factor receptor mutation. Kaplan-Meier survival analysis showed that the NIA-present group displayed a better prognosis than the NIA-absent group in disease-free survival (DFS) and overall survival (OS) (5-year DFS 94.6% vs. 87.2%, 5-year OS 97.2% vs. 91.1%). However, after adjusting for clinicopathological factors by propensity score matching, no significant differences in prognosis were identified between the NIA-present and NIA-absent groups (5-year DFS 92.4% vs 89.6%, 5-year OS 95.6% vs 94.3%). CONCLUSIONS: Our current study suggests that the prognostic impact of the presence of NIAs on lung adenocarcinoma is due to differences in clinicopathological factors.

Skeletal muscle area predicts the outcomes of non-small-cell lung cancer after trimodality therapy.

OBJECTIVES: Sarcopenia correlates with poor prognosis in various malignancies. However, the prognostic significance of sarcopenia remains to be determined in patients with non-small-cell lung cancer who undergo surgery after receiving neoadjuvant chemoradiotherapy (NACRT). METHODS: We retrospectively reviewed the patients with stage II/III non-small-cell lung cancer who underwent surgery following NACRT. The paravertebral skeletal muscle area (SMA) (cm2) at the 12th thoracic vertebra level was measured. We calculated the SMA index (SMAI) as SMA/squared height (cm2/m2). Patients were divided into low and high SMAI groups, and the association of SMAI with clinicopathological factors and prognosis was assessed. RESULTS: The patients' [men, 86 (81.1%)] median age was 63 (21-76) years. There were 106 patients including 2 (1.9%), 10 (9.4%), 74 (69.8%), 19 (17.9%) and 1 (0.9%) patients with stage IIA, IIB, IIIA, IIIB and IIIC, respectively. Of the patients, 39 (36.8%) and 67 (63.2%) were classified in the low and the high SMAI groups, respectively. Kaplan-Meier analysis showed that the low group had a significantly shorter overall survival and disease-free survival than the high group. Multivariable analysis identified low SMAI as an independent poor prognostic factor for overall survival. CONCLUSIONS: Pre-NACRT SMAI correlates with poor prognosis; therefore, assessing sarcopenia based on pre-NACRT SMAI may help determine optimal treatment strategies and suitable nutritional and exercise interventions.

Prognostic Impact of C-Reactive Protein-to-Lymphocyte Ratio in Non-small Cell Lung Cancer: A Propensity Score-Matching Analysis.

BACKGROUND: Many inflammatory and nutritional markers have been used to predict prognosis in lung cancer. The C-reactive protein (CRP)-to-lymphocyte ratio (CLR) is a useful prognostic factor in various cancers. However, the prognostic value of preoperative CLR in patients with non-small cell lung cancer (NSCLC) remains to be established. We examined the significance of the CLR compared with known markers. METHODS: A total of 1380 surgically resected NSCLC patients treated at two centers were recruited and divided into derivation and validation cohorts. After CLRs were calculated, patients were classified into high and low CLR groups based on the cutoff value determined by receiver operating characteristics curve analysis. Subsequently, we determined the statistical associations of the CLR with clinicopathological factors and prognosis and further analyzed its prognostic impact by propensity-score matching. RESULTS: Of all the inflammatory markers examined, CLR yielded the highest area-under-the-curve value. The prognostic impact of CLR remained significant after propensity-score matching. Prognosis was significantly worse in the high-CLR group than in the low-CLR group (5-year, disease-free survival [DFS]: 58.1% vs. 81.9%, P < 0.001; 5-year overall survival [OS]: 72.1% vs. 91.2%, P < 0.001). The results were confirmed in the validation cohorts. Multivariable analysis also showed high CLR as an independent factor for both DFS and OS (DFS: hazard ratio [HR] 1.42, P = 0.027; OS: HR 1.95, P = 0.0037). CONCLUSIONS: Preoperative CLR is a useful marker for predicting the prognosis of NSCLC patients who have undergone surgery.

Preventive effect of tertiary lymphoid structures on lymph node metastasis of lung adenocarcinoma.

BACKGROUND: Ectopic lymphoid formations are called tertiary lymphoid structures (TLSs). TLSs in cancer have been reported to be associated with good prognosis and immunotherapy response. However, the relationship between TLSs and lymph node (LN) metastasis is unclear. METHODS: We analyzed 218 patients with radically resected lung adenocarcinoma. TLSs were defined as the overlap of T cell zone and B cell zone. Granzyme B + cells were defined as cytotoxic lymphocytes. We evaluated phenotypes of lymphocytes in TLSs, tumor-infiltrating lymphocytes (TILs) and LNs by immunohistochemistry. We divided the patients into mature TLS (DC-Lamp high) and immature TLS (DC-Lamp low) groups. The relationship between TLS maturation and clinicopathological factors was analyzed. RESULTS: The mature TLS group was associated with significantly lower frequency of LN metastasis (P < 0.0001) and early cancer stage (P = 0.0049). The mature TLS group had significantly more CD8 + (P = 0.0203) and Foxp3 + (P = 0.0141) cells in TILs than the immature TLS group had. Mature TLSs were independently associated with a favorable overall survival (hazard ratio [HR] = 0.17, P = 0.0220) and disease-free survival (HR = 0.54, P = 0.0436). Multivariate analysis showed that mature TLS was an independent low-risk factor for LN metastasis (odds ratio = 0.06, P = 0.0003). The number of cytotoxic lymphocytes in LNs was higher in the mature TLS group than in the immature group (20.0 vs. 15.1, P = 0.017). CONCLUSION: Mature TLSs were associated with an increased number of cytotoxic lymphocytes in draining LNs, a lower frequency of LN metastasis, and favorable outcomes. Mature TLSs may support antitumor immunity by lymphocyte activation.

Necitumumab plus gemcitabine and cisplatin in previously treated lung squamous cell carcinoma.

BACKGROUND: The efficacy and safety of the anti-EGFR antibody necitumumab combined with gemcitabine and cisplatin (N + GC) in the first-line treatment of advanced lung squamous cell carcinoma (LSCC) have been proven. However, the efficacy and safety of N + GC in the second line or later treatment remain unclear. METHODS: Eleven patients who received N + GC for advanced-stage or recurrent LSCC were enrolled. We retrospectively assessed the patients' clinical characteristics and efficacy and safety of treatment. RESULTS: The median patient age was 73 years (range, 63-77 years). The cohort included nine (81.8%) men and two (18.2%) women. Two (18.2%) patients had postoperative recurrence, and one (9.1%), three (27.3%), one (9.1%), and four (36.4%) patients were diagnosed with stage IIIA, IIIB, IVA, and IVB disease, respectively. Concerning the best overall response, partial response was achieved in five (45.5%) patients, four (36.4%) patients displayed stable disease, and two (18.2%) patients were not evaluable. Median progression-free survival was 6.8 months (range, 1.4-10.3 months). The grade 3 or higher neutropenia, thrombocytopenia, and anemia occurred in six (54.5%), three (27.3%), and two (18.2%) patients, respectively. Additionally, grade 3 skin reaction, rash, lung infection, duodenal ulcer, and febrile neutropenia were observed in one (9.1%) patient each. Two (18.2%) patients required treatment interruption because of adverse events. CONCLUSION: N + GC displayed good efficacy in the second line or later treatment among patients with LSCC. This study suggested that N + GC is a useful option even after second-line treatment of advanced-stage or recurrent LSCC, although the management of adverse events is essential.

Case report: Success of tepotinib therapy in overcoming resistance to osimertinib in a patient with EGFR-mutant lung adenocarcinoma with a potential acquired MET exon 14 skipping mutation.

Osimertinib is a standard therapy for the treatment of advanced non-small cell lung cancer (NSCLC) harboring epidermal growth factor receptor gene (EGFR) mutations, but most patients with EGFR-mutant NSCLC develop secondary resistance to osimertinib. Mesenchymal-epithelial transition gene (MET) alterations and oncogene fusions have been identified as the most common mechanisms of resistance to osimertinib. However, MET exon 14 skipping mutation (METex14del) as an acquired resistance to osimertinib has rarely been reported. A non-smoking 76-year-old woman was diagnosed with lung adenocarcinoma in the right lower lobe (cT2bN2M1c [pulmonary and bone metastases], cStage IVB). The primary tumor was submitted to cobas® EGFR Mutation Test v2 (Roche Diagnostics Ltd.), next generation sequencing (Oncomine Comprehensive Assay v3; Thermo Fisher Scientific), the AmoyDx® Essential NGS panel (Amoy Diagnostics, Xiamen, China), all of which were positive for EGFR L858R and de novo T790M. We administered daily osimertinib (80 mg/day), and achieved a partial response. However, after 14.0 months, computed tomography showed progression of the primary tumor and lung metastases. Re-biopsy of the primary tumor was conducted, and the specimen was submitted to Archer®MET companion diagnostic for detection of METex14del. Although the primary tumor was negative for METex14del, the re-biopsy specimen was positive for METex14del. We validated that the biopsy specimen of the primary tumor at diagnosis before osimertinib administration was negative for METex14del using local reverse transcription PCR. We administered daily tepotinib (500 mg/day) to the patient as a further-line treatment, and achieved a partial response (tumor shrinkage rate: 34.5%) after 2.0 months, who responded to tepotinib therapy for 8.0 months. We described a patient with lung adenocarcinoma harboring METex14del as a potential acquired resistance to osimertinib, who responded to subsequent tepotinib therapy. Re-biopsy and re-analysis of genetic profiles should be considered in NSCLC patients who develop osimertinib resistance.