Neoadjuvant Chemoimmunotherapy for NSCLC: A Systematic Review and Meta-Analysis.

Importance: To date, no meta-analyses have comprehensively assessed the association of neoadjuvant chemoimmunotherapy with clinical outcomes in non-small cell lung cancer (NSCLC) in randomized and nonrandomized settings. In addition, there exists controversy concerning the efficacy of neoadjuvant chemoimmunotherapy for patients with NSCLC with programmed cell death 1 ligand 1 (PD-L1) levels less than 1%. Objective: To compare neoadjuvant chemoimmunotherapy with chemotherapy by adverse events and surgical, pathological, and efficacy outcomes using recently published randomized clinical trials and nonrandomized trials. Data Sources: MEDLINE and Embase were systematically searched from January 1, 2013, to October 25, 2023, for all clinical trials of neoadjuvant chemoimmunotherapy and chemotherapy that included at least 10 patients. Study Selection: Observational studies and trials reporting the use of neoadjuvant radiotherapy, including chemoradiotherapy, molecular targeted therapy, or immunotherapy monotherapy, were excluded. Main Outcomes and Measures: Surgical, pathological, and efficacy end points and adverse events were pooled using a random-effects meta-analysis. Results: Among 43 eligible trials comprising 5431 patients (4020 males [74.0%]; median age range, 55-70 years), there were 8 randomized clinical trials with 3387 patients. For randomized clinical trials, pooled overall survival (hazard ratio, 0.65; 95% CI, 0.54-0.79; I2 = 0%), event-free survival (hazard ratio, 0.59; 95% CI, 0.52-0.67; I2 = 14.9%), major pathological response (risk ratio, 3.42; 95% CI, 2.83-4.15; I2 = 31.2%), and complete pathological response (risk ratio, 5.52; 95% CI, 4.25-7.15; I2 = 27.4%) favored neoadjuvant chemoimmunotherapy over neoadjuvant chemotherapy. For patients with baseline tumor PD-L1 levels less than 1%, there was a significant benefit in event-free survival for neoadjuvant chemoimmunotherapy compared with chemotherapy (hazard ratio, 0.74; 95% CI, 0.62-0.89; I2 = 0%). Conclusion and Relevance: This study found that neoadjuvant chemoimmunotherapy was superior to neoadjuvant chemotherapy across surgical, pathological, and efficacy outcomes. These findings suggest that patients with resectable NSCLC with tumor PD-L1 levels less than 1% may have an event-free survival benefit with neoadjuvant chemoimmunotherapy.

Transitioning to Neoadjuvant Therapy for Resectable Non-Small Cell Lung Cancer: Trends and Surgical Outcomes in a Regionalized Pulmonary Oncology Network.

BACKGROUND: Several regulatory agencies have approved the use of the neoadjuvant chemo-immunotherapy for resectable stage II and III of non-small cell lung cancer (NSCLC) and numerous trials investigating novel agents are underway. However, significant concerns exist around the feasibility and safety of offering curative surgery to patients treated within such pathways. The goal in this study was to evaluate the impact of a transition towards a large-scale neoadjuvant therapy program for NSCLC. METHODS: Medical charts of patients with clinical stage II and III NSCLC who underwent resection from January 2015 to December 2020 were reviewed. The primary outcome was perioperative complication rate between neoadjuvant-treated versus upfront surgery patients. Multivariable logistic regression estimated occurrence of postoperative complications and overall survival was assessed as an exploratory secondary outcome by Kaplan-Meier and Cox-regression analyses. RESULTS: Of the 428 patients included, 106 (24.8%) received neoadjuvant therapy and 322 (75.2%) upfront surgery. Frequency of minor and major postoperative complications was similar between groups (P = .22). Occurrence in postoperative complication was similar in both cohort (aOR = 1.31, 95% CI 0.73-2.34). Neoadjuvant therapy administration increased from 10% to 45% with a rise in targeted and immuno-therapies over time, accompanied by a reduced rate of preoperative radiation therapy use. 1-, 2-, and 5-year overall survival was higher in neoadjuvant therapy compared to upfront surgery patients (Log-Rank P = .017). CONCLUSIONS: No significant differences in perioperative outcomes and survival were observed in resectable NSCLC patients treated by neoadjuvant therapy versus upfront surgery. Transition to neoadjuvant therapy among resectable NSCLC patients is safe and feasible from a surgical perspective.

Fetal Type Morphologies Suggest the Presence of DICER1 Hotspot Mutations in Non-small Cell Lung Cancer.

Germline and somatic pathogenic variants (PVs) in DICER1 , encoding a miRNA biogenesis protein, are associated with a wide variety of highly specific pathologic entities. The lung tumors pleuropulmonary blastoma, pulmonary blastoma (PB), and well-differentiated fetal lung adenocarcinoma (WDFLAC) are all known to harbor DICER1 biallelic variants (loss of function and/or somatic hotspot missense mutations), and all share pathologic features reminiscent of the immature lung. However, the role of DICER1 PVs in non-small cell lung cancer (NSCLC) is relatively unknown. Here, we aimed to establish the spectrum of lung pathologies associated with DICER1 hotspot PVs and to compare the mutational landscape of DICER1 -mutated NSCLC with and without hotspots. We queried DNA sequencing data from 12,146 NSCLCs featuring somatic DICER1 variants. 235 (1.9%) cases harboring ≥ 1 DICER1 PV were found and 9/235 (3.8%) were DICER1 hotspot-positive cases. Histologic review of DICER1 hotspot-positive cases showed that all but one tumor were classified as within the histologic spectrum of PB/WDFLAC, whereas all the DICER1 non-hotspot double variants were classified as lung adenocarcinomas, not otherwise specified. Comparison between the mutational landscape of DICER1 hotspot-positive and hotspot-negative cases revealed a higher frequency of CTNNB1 mutations in the hotspot-positive cases (5/9 vs. 2/225; P <0.00001). We conclude that DICER1 somatic hotspots are not implicated in the most common forms of NSCLC but rather select for morphologic features of lung tumor types such as PB and WDFLAC. As a corollary, cases showing this tumor morphology should undergo testing for DICER1 variants, and if positive, genetic counseling should be considered.

Esophagectomy versus observation following endoscopic submucosal dissection of pT1b esophageal adenocarcinoma.

BACKGROUND: Management following endoscopic submucosal dissection (ESD) of pT1b esophageal adenocarcinoma (EAC) remains controversial. This study compared pathological and survival outcomes of patients after endoscopic resection (ER) of pT1b EAC followed by either en bloc esophagectomy or observation. METHODS: From 1/12 to 12/22, all patients with pT1b EAC treated with ER were identified from a prospectively maintained departmental database. ESD was curative (all of: Submucosal invasion < 500 µm; G1/2, LVI/PNI-; deep margin-) or non-curative (one or more of Submucosal invasion ≥ 500 µm; G3; LVI/PNI+; deep margin+). Patients were allocated to observation (OBS) or esophagectomy (SURG) based on patient factors/preference and pathological variables. RESULTS: 56/171 ERs met the inclusion criteria. ER was curative in 8/56 (14%) and non-curative in 48/56 (86%). OBS was undertaken after 8/27 (30%) curative and 19/27 (70%) non-curative resections. All 29 SURG patients had non-curative ERs and were younger, had lower Charlson comorbidity scores and had more deep margin + lesions than OBS patients. Post-esophagectomy, 15/29 (52%) had no residual disease within the surgical specimen while pT+N-/pT-N+/pT+N+ occurred in 5/3/6 (17%/10%/21%) patients. Of those with residual disease in the surgical specimen, 12/14 (86%) had deep margin + ERs; however, only ESD instead of EMR was independently associated with a lower risk of residual disease (OR 0.431, 95% CI - 0.016 to 1.234, p = 0.045). OBS and SURG patients had equivalent overall survival outcomes and recurrence was low in both groups even following non-curative ER. Follow-up was 28 months (0-102) and 30 months (0-97), respectively. CONCLUSION: In select patients, including some of those with a non-curative ESD resection of pT1B EAC, surveillance alone may be appropriate. Alternatives beyond traditional pathological features is needed to direct patient care more accurately.

Canadian Consensus Recommendations for the Management of Operable Stage II/III Non-Small-Cell Lung Cancer: Results of a Modified Delphi Process.

The treatment paradigm for patients with stage II/III non-small-cell lung cancer (NSCLC) is rapidly evolving. We performed a modified Delphi process culminating at the Early-stage Lung cancer International eXpert Retreat (ELIXR23) meeting held in Montreal, Canada, in June 2023. Participants included medical and radiation oncologists, thoracic surgeons and pathologists from across Quebec. Statements relating to diagnosis and treatment paradigms in the preoperative, operative and postoperative time periods were generated and modified until all held a high level of consensus. These statements are aimed to help guide clinicians involved in the treatment of patients with stage II/III NSCLC.

A Deep Learning-Based Approach to Estimate Paneth Cell Granule Area in Celiac Disease.

CONTEXT.­: Changes in Paneth cell numbers can be associated with chronic inflammatory diseases of the gastrointestinal tract. So far, no consensus has been achieved on the number of Paneth cells and their relevance to celiac disease (CD). OBJECTIVES.­: To compare crypt and Paneth cell granule areas between patients with CD and without CD (non-CD) using an artificial intelligence-based solution. DESIGN.­: Hematoxylin-eosin-stained sections of duodenal biopsies from 349 patients at the McGill University Health Centre were analyzed. Of these, 185 had a history of CD and 164 were controls. Slides were digitized and NoCodeSeg, a code-free workflow using open-source software (QuPath, DeepMIB), was implemented to train deep learning models to segment crypts and Paneth cell granules. The total area of the entire analyzed tissue, epithelium, crypts, and Paneth cell granules was documented for all slides, and comparisons were performed. RESULTS.­: A mean intersection-over-union score of 88.76% and 91.30% was achieved for crypt areas and Paneth cell granule segmentations, respectively. On normalization to total tissue area, the crypt to total tissue area in CD was increased and Paneth cell granule area to total tissue area decreased when compared to non-CD controls. CONCLUSIONS.­: Crypt hyperplasia was confirmed in CD compared to non-CD controls. The area of Paneth cell granules, an indirect measure of Paneth cell function, decreased with increasing severity of CD. More importantly, our study analyzed complete hematoxylin-eosin slide sections using an efficient and easy to use coding-free artificial intelligence workflow.

BCG administration promotes the long-term protection afforded by a single-dose intranasal adenovirus-based SARS-CoV-2 vaccine.

Recent publications have explored intranasal (i.n.) adenovirus-based (Ad) vaccines as an effective strategy for SARS-CoV-2 in pre-clinical models. However, the effects of prior immunizations and infections have yet to be considered. Here, we investigate the immunomodulatory effects of Mycobacterium bovis BCG pre-immunization followed by vaccination with an S-protein-expressing i.n. Ad, termed Ad(Spike). While i.n. Ad(Spike) retains some protective effect after 6 months, a single administration of BCG-Danish prior to Ad(Spike) potentiates its ability to control viral replication of the B.1.351 SARS-CoV-2 variant within the respiratory tract. Though BCG-Danish did not affect Ad(Spike)-generated humoral immunity, it promoted the generation of cytotoxic/Th1 responses over suppressive FoxP3+ TREG cells in the lungs of infected mice. Thus, this vaccination strategy may prove useful in limiting future pandemics by potentiating the long-term efficacy of mucosal vaccines within the context of the widely distributed BCG vaccine.

Routine Clinically Detected Increased ROS1 Transcripts Are Related With ROS1 Expression by Immunohistochemistry and Associated With EGFR Mutations in Lung Adenocarcinoma.

Introduction: Translocations of the ROS1 gene were found to drive tumorigenesis in 1% to 2% of lung adenocarcinoma. In clinical practice, ROS1 rearrangements are often screened by immunohistochemistry (IHC) before confirmation with either fluorescence in situ hybridization or molecular techniques. This screening test leads to a non-negligible number of cases that have equivocal or positive ROS1 IHC, without ROS1 translocation. Methods: In this study, we have analyzed retrospectively 1021 cases of nonsquamous NSCLC having both ROS1 IHC and molecular analysis using next-generation sequencing. Results: ROS1 IHC was negative in 938 cases (91.9%), equivocal in 65 cases (6.4%), and positive in 18 cases (1.7%). Among these 83 equivocal or positive cases, only two were ROS1 rearranged, leading to a low predictive positive value of the IHC test (2%). ROS1-positive IHC was correlated with an increased mRNA ROS1 transcripts. Moreover, we have found a mean statistically significant relationship between ROS1 expression and EGFR gene mutations, suggesting a crosstalk mechanism between these oncogenic driver molecules. Conclusion: This study demonstrates that ROS1 IHC represents true ROS1 mRNA expression, and raises the question of a potential benefit of combined targeted therapy in EGFR-mutated NSCLC.

Concerted epithelial and stromal changes during progression of Barrett's Esophagus to invasive adenocarcinoma exposed by multi-scale, multi-omics analysis.

Esophageal adenocarcinoma arises from Barrett's esophagus, a precancerous metaplastic replacement of squamous by columnar epithelium in response to chronic inflammation. Multi-omics profiling, integrating single-cell transcriptomics, extracellular matrix proteomics, tissue-mechanics and spatial proteomics of 64 samples from 12 patients' paths of progression from squamous epithelium through metaplasia, dysplasia to adenocarcinoma, revealed shared and patient-specific progression characteristics. The classic metaplastic replacement of epithelial cells was paralleled by metaplastic changes in stromal cells, ECM and tissue stiffness. Strikingly, this change in tissue state at metaplasia was already accompanied by appearance of fibroblasts with characteristics of carcinoma-associated fibroblasts and of an NK cell-associated immunosuppressive microenvironment. Thus, Barrett's esophagus progresses as a coordinated multi-component system, supporting treatment paradigms that go beyond targeting cancerous cells to incorporating stromal reprogramming.

Stereotactic ablative radiotherapy before resection to avoid delay for early-stage lung cancer or oligometastases during the COVID-19 pandemic: Pathologic outcomes from the SABR-BRIDGE protocol.

BACKGROUND: During coronavirus disease 2019 (COVID-19)-related operating room closures, some multidisciplinary thoracic oncology teams adopted a paradigm of stereotactic ablative radiotherapy (SABR) as a bridge to surgery, an approach called SABR-BRIDGE. This study presents the preliminary surgical and pathological results. METHODS: Eligible participants from four institutions (three in Canada and one in the United States) had early-stage presumed or biopsy-proven lung malignancy that would normally be surgically resected. SABR was delivered using standard institutional guidelines, with surgery >3 months following SABR with standardized pathologic assessment. Pathological complete response (pCR) was defined as absence of viable cancer. Major pathologic response (MPR) was defined as ≤10% viable tissue. RESULTS: Seventy-two patients underwent SABR. Most common SABR regimens were 34 Gy/1 (29%, n = 21), 48 Gy/3-4 (26%, n = 19), and 50/55 Gy/5 (22%, n = 16). SABR was well-tolerated, with one grade 5 toxicity (death 10 days after SABR with COVID-19) and five grade 2-3 toxicities. Following SABR, 26 patients underwent resection thus far (13 pending surgery). Median time-to-surgery was 4.5 months post-SABR (range, 2-17.5 months). Surgery was reported as being more difficult because of SABR in 38% (n = 10) of cases. Thirteen patients (50%) had pCR and 19 (73%) had MPR. Rates of pCR trended higher in patients operated on at earlier time points (75% if within 3 months, 50% if 3-6 months, and 33% if ≥6 months; p = .069). In the exploratory best-case scenario analysis, pCR rate does not exceed 82%. CONCLUSIONS: The SABR-BRIDGE approach allowed for delivery of treatment during a period of operating room closure and was well-tolerated. Even in the best-case scenario, pCR rate does not exceed 82%.

The 8th Edition TNM Stage Reclassification of T4 Non-Small Cell Lung Cancer: A Granular Examination of Short and Long-Term Outcomes.

INTRODUCTION: Whilst the American Joint Committee on Cancer 7th edition (AJCC7) classified pT4 non-small-cell lung cancers (NSCLC) as those with extra-pulmonary invasion, the revised 8th edition (AJCC8) included tumors > 7cm regardless of extra-pleural spread. We examined perioperative and long-term outcomes of classical T4 definitions with patients whose tumors were greater than 7cm without extra-pulmonary invasion. MATERIALS AND METHODS: A retrospective single center cohort study was performed. All consecutive patients with pT4 lesions between 2011 and 2018 were identified based on either the AJCC7 or AJCC8 classification. Clinicopathological variables were extracted and compared in a univariate manner. A multivariate Cox regression analysis was performed to assess factors associated with overall survival. RESULTS: Forty patients were allocated to AJCC7 and 118 to AJCC8. Patients in the former were more likely to have positive lymph nodes, synchronous metastasis, multifocal disease and lymphovascular invasion. AJCC7 patients were more likely to undergo pneumonectomy despite significantly more being treated with neoadjuvant therapy. Ninety-day mortality was higher in the AJCC7 group. There was no difference in long-term overall survival. On multivariate analysis male gender, squamous cell histology and increasing tumor size were associated with an increased risk of death. CONCLUSION: Although long-term outcomes were similar, the heterogenicity within the AJCC8 classification emphasizes the need to contextualize the perioperative outcomes for patients with pT4 NSCLC. These data are important for future iterations of the TNM classification in view of emerging neoadjuvant options for patients with cT4 operable NSCLC.

Germline EGFR c.2527G > A (p.V843I) variant and familial lung cancer.

BACKGROUND: Somatic epidermal growth factor receptor (EGFR) pathogenic variants have been identified and are routinely tested in the molecular diagnosis of non-small cell lung cancer (NSCLC) as they represent a target for EGFR tyrosine kinase inhibitor (TKI) therapy. However, germline variants in EGFR are much less frequently reported. CASE PRESENTATION: Herein, we report the case of a 46-year-old woman diagnosed with lung adenocarcinoma who was found to harbor a rare germline missense variant in exon 21 of EGFR: NM_005228.5(EGFR):c.2527G>A (p.V843I). In the tumor, this variant (Cosmic ID COSV51767379) was accompanied by a secondary, known pathogenic EGFR variant in cis, also occurring in exon 21, c.2573T>G (p.L858R) (Cosmic ID 6224). Her mother was previously diagnosed with poorly differentiated lung carcinoma and her tumor was also found to harbour the p.V843I variant but no other pathogenic variants. Notably, the proband's sister, diagnosed with a lung carcinoma with sarcomatous features at age 44, did not carry this variant or any other somatic or germline EGFR variants. CONCLUSION: This is the second report of familial lung adenocarcinoma associated with the germline p.V843I variant, which remains classified as a variant of uncertain significance. The lack of segregation of this variant in the proband's affected sister illustrates the complexity with evaluating lung cancer predisposition factors. Currently, there is a paucity of data regarding the therapeutic outcomes of patients with tumors expressing this rare germline variant, therefore we propose an algorithm for the identification of at-risk individuals and families as the first step for their personalized management.

Obesity alters monocyte developmental trajectories to enhance metastasis.

Obesity is characterized by chronic systemic inflammation and enhances cancer metastasis and mortality. Obesity promotes breast cancer metastasis to lung in a neutrophil-dependent manner; however, the upstream regulatory mechanisms of this process remain unknown. Here, we show that obesity-induced monocytes underlie neutrophil activation and breast cancer lung metastasis. Using mass cytometry, obesity favors the expansion of myeloid lineages while restricting lymphoid cells within the peripheral blood. RNA sequencing and flow cytometry revealed that obesity-associated monocytes resemble professional antigen-presenting cells due to a shift in their development and exhibit enhanced MHCII expression and CXCL2 production. Monocyte induction of the CXCL2-CXCR2 axis underlies neutrophil activation and release of neutrophil extracellular traps to promote metastasis, and enhancement of this signaling axis is observed in lung metastases from obese cancer patients. Our findings provide mechanistic insight into the relationship between obesity and cancer by broadening our understanding of the interactive role that myeloid cells play in this process.

A Simplified Version of the IASLC Grading System for Invasive Pulmonary Adenocarcinomas With Improved Prognosis Discrimination.

Tumor grading enables better management of patients and treatment options. The International Association for the Study of Lung Cancer (IASLC) Pathology Committee has recently released a 3-tier grading system for invasive pulmonary adenocarcinoma consisting of predominant histologic patterns plus a cutoff of 20% of high-grade components including solid, micropapillary, and complex glandular patterns. The goal of this study was to validate the prognostic value of the new IASLC grading system and to compare its discriminatory performance to the predominant pattern-based grading system and a simplified version of the IASLC grading system without complex glandular patterns. This was a single-site retrospective study based on a 20-year data collection of patients that underwent lung cancer surgery. All invasive pulmonary adenocarcinomas confirmed by the histologic review were evaluated in a discovery cohort (n=676) and a validation cohort (n=717). The median duration of follow-up in the combined dataset (n=1393) was 7.5 years. The primary outcome was overall survival after surgery. The 3 grading systems had strong and relatively similar predictive performance, but the best parsimonious model was the simplified IASLC grading system (log-rank P =1.39E-13). The latter was strongly associated with survival in the validation set ( P =1.1E-18) and the combined set ( P =5.01E-35). We observed a large proportion of patients upgraded to the poor prognosis group using the IASLC grading system, which was attenuated when using the simplified IASLC grading system. In conclusion, we identified a histologic simpler classification for invasive pulmonary adenocarcinomas that outperformed the recently proposed IASLC grading system. A simplified grading system is clinically convenient and will facilitate widespread implementation.

Next-generation sequencing of non-small cell lung cancer at a Quebec health care cancer centre.

BACKGROUND: Lung cancer is the leading cause of cancer death in both men and women. Quebec has the highest lung cancer mortality out of all provinces in Canada, believed to be caused by higher smoking rates. Molecular testing for lung cancer is standard of care due to the discovery of actionable driver mutations that can be targeted with tyrosine kinase inhibitors. To date, no detailed molecular testing characterization of Quebec patients with lung cancer using next generation sequencing (NGS) has been performed. MATERIALS AND METHODS: The aim of this study was to describe the genomic landscape of patients with lung cancer (n = 997) who underwent NGS molecular testing at a tertiary care center in Quebec and to correlate it with clinical and pathology variables. RESULTS: Compared to 10 other NGS studies found through a structured search strategy, our cohort had a higher prevalence of KRAS mutations (39.2%) compared to most geographical locations. Additionally, we observed a significant positive association between decreasing age and a higher proportion of KRAS G12C mutations. CONCLUSION: Overall, it remains important to assess institutional rates of actionable driver mutations to help guide governing bodies, fuel clinical trials and create benchmarks for expected rates as quality metrics.

Single-cell spatial landscapes of the lung tumour immune microenvironment.

Single-cell technologies have revealed the complexity of the tumour immune microenvironment with unparalleled resolution1-9. Most clinical strategies rely on histopathological stratification of tumour subtypes, yet the spatial context of single-cell phenotypes within these stratified subgroups is poorly understood. Here we apply imaging mass cytometry to characterize the tumour and immunological landscape of samples from 416 patients with lung adenocarcinoma across five histological patterns. We resolve more than 1.6 million cells, enabling spatial analysis of immune lineages and activation states with distinct clinical correlates, including survival. Using deep learning, we can predict with high accuracy those patients who will progress after surgery using a single 1-mm2 tumour core, which could be informative for clinical management following surgical resection. Our dataset represents a valuable resource for the non-small cell lung cancer research community and exemplifies the utility of spatial resolution within single-cell analyses. This study also highlights how artificial intelligence can improve our understanding of microenvironmental features that underlie cancer progression and may influence future clinical practice.

Relation between mismatch repair status, chemoresponse, survival and anatomic location in gastroesophageal adenocarcinoma.

BACKGROUND: It has recently been reported that mismatch repair (MMR) status and microsatellite instability (MSI) status in gastroesophageal carcinomas predict surgical, chemotherapeutic and immunotherapeutic outcomes; however, there is extensive variability in the reported incidence and clinical implications of MMR/MSI status in gastroesophaegal adenocarcinomas. We characterized a Canadian surgical patient cohort with respect to MMR status, clinicopathologic correlates and anatomic tumour location. METHODS: We investigated MMR and BRAF V600E status of gastroesophaegal adenocarcinomas in patients who underwent gastrectomy or esophagectomy with extended (D2) lymphadenectomy at a single centre between 2011 and 2019. We correlated patterns of MMR expression in the overall cohort and in anatomic location-defined subgroups with treatment response and overall survival using multivariate analysis. RESULTS: In all, 226 cases of gastroesophaegal adenocarcinoma (63 esophageal, 98 gastroesophageal junctional and 65 gastric) were included. The MMR-deficient (dMMR) immunophenotype was found in 28 tumours (12.3%) (15 junctional [15.3%], 13 gastric [20.0%] and none of the esophageal). The majority (25 [89%]) of dMMR cases showed MLH1/PMS2 loss without concurrent BRAF V600E mutation. Two MSH2/ MSH6-deficient gastric tumours and 1 MSH6-deficient junctional tumour were detected. The pathologic response to preoperative chemotherapy was comparable in the dMMR and MMR-proficient (pMMR) cohorts. However, dMMR status was associated with significantly longer median overall survival than pMMR status (5.8 yr v. 2.4 yr, hazard ratio [HR] 1.91, 95% confidence interval [CI] 1.06-3.46), particularly in junctional tumours (4.6 yr v. 1.9 yr, HR 2.97, 95% CI 1.27-6.94). CONCLUSION: Our study shows that MMR status has at least prognostic value, which supports the need for biomarker testing in gastroesophageal adenocarcinomas, including junctional adenocarcinomas. This highlights the clinical significance of determining the MMR status in all adenocarcinomas of the upper gastrointestinal tract. Response to induction chemotherapy, however, was not influenced by MMR status.