Search Results (407)

Urothelial carcinoma (UC) is a biologically and clinically heterogeneous disease arising from the bladder and upper urinary tract. Immune checkpoint inhibitors (ICIs) have transformed treatment of advanced UC, yet durable responses remain limited to a minority of patients, underscoring the need to better understand the tumor immune microenvironment (TME). This narrative review examines the UC immune phenotype across disease stages and anatomical sites, integrating evidence from bulk and single-cell transcriptomics, spatial profiling, and translational studies. We describe the principal immune cell populations of the UC TME—including cytotoxic and regulatory T cells, macrophages, myeloid-derived suppressor cells, natural killer cells, B cells, and dendritic cells—and their relationship to established molecular subtypes. We review how this immune landscape evolves from non-muscle-invasive to metastatic disease, including the distinct contexture of upper tract UC and variant histology. We critically evaluate established ICI biomarkers (PD-L1, FGFR3, tumor mutational burden, mismatch repair deficiency) alongside emerging candidates—tumor-infiltrating lymphocyte density, HLA class I expression, tertiary lymphoid structures, and multiparameter transcriptomic scores—noting that most remain investigational and require prospective validation before clinical use. Finally, we address key biological, technical, and clinical barriers to this research and outline future directions in AI-assisted digital pathology and multimodal biomarker integration. A comprehensive characterization of UC immune phenotype is essential to guide rational, biomarker-driven patient selection and optimize next-generation immunotherapy strategies. Full article

Temozolomide (TMZ) remains the cornerstone of chemotherapeutic agent for glioblastoma (GBM), yet intrinsic and acquired resistance severely limits its clinical benefit. While O⁶-methylguanine-DNA methyltransferase (MGMT)–mediated repair of TMZ-induced O6-methylguanine (O⁶-meG) lesions has been extensively studied, the DNA mismatch repair (MMR) pathway is increasingly recognized as a key determinant of TMZ cytotoxicity. Canonical MMR, mediated by MutSα (MSH2–MSH6) and MutLα (MLH1–PMS2) complexes, recognizes O⁶-meG: thymine mispairs generated during replication and initiates futile repair cycles that culminate in replication stress, replication fork collapse, and apoptotic signaling; intact canonical MMR is, therefore, required for TMZ-induced cell death. Disruption of canonical MMR, frequently via acquired MSH6 mutations, confers TMZ tolerance and drives hypermutated recurrent GBM. Beyond mismatch correction, MMR proteins perform non-canonical functions in DNA damage signaling, replication stress responses, transcriptional regulation, chromatin dynamics, and immune modulation. These activities may shift the outcome from cytotoxic futile repair toward replication stress adaptation, Translesion synthesis (TLS)-mediated lesion tolerance, immune remodeling, and therapeutic resistance. Notably, partial attenuation or functional diversion of MMR may decouple lesion recognition from cytotoxic signaling, enabling TLS-mediated lesion tolerance without complete loss of MMR activity. This review integrates current insights into canonical and non-canonical MMR functions in GBM, defines their distinct contributions to TMZ sensitivity and resistance, and highlights therapeutic opportunities to exploit MMR-associated dependencies, including synthetic lethal strategies and immunotherapeutic vulnerabilities linked to MMR deficiency-driven hypermutation. Full article

The 27th annual Western Canadian Gastrointestinal Cancer Consensus Conference (WCGCCC) was held in Calgary, Alberta, on 26–27 September 2025. The WCGCCC is an interactive multidisciplinary conference that was attended by healthcare professionals from across Western Canada (British Columbia, Alberta, Saskatchewan, and Manitoba) who are involved in the care of patients with colorectal cancer. Specialists from the fields of medical and radiation oncology, pathology, surgery, and a family physician in oncology participated in presentations and discussions for the purpose of developing the recommendations presented here. This consensus statement addresses recent advances in the management of colorectal cancer in a Western Canadian context, with respect to adjuvant exercise, as per the CHALLENGE trial, adjuvant Aspirin and PI3K testing, as per the ALASCCA trial, adjuvant immunotherapy, as per the ATOMIC trial, the use of encorafenib and an EGFR inhibitor with chemotherapy, as per the BREAKWATER trial, the use of combination immunotherapy as per the CHECKMATE 8HW trial and optimal strategies for omitting radiation and non-operative management of non-metastatic rectal cancer. Full article

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most lethal malignancies, with a rising incidence and a poor prognosis that largely reflects late-stage diagnosis. Although most cases are sporadic, approximately 5–10% of PDACs occur in the context of inherited cancer susceptibility, including hereditary pancreatic cancer (HPC) syndromes and familial pancreatic cancer (FPC). Germline pathogenic variants in genes involved in DNA damage repair, cell-cycle regulation, and genomic stability—such as BRCA1, BRCA2, PALB2, ATM, CDKN2A, STK11, mismatch repair genes, and TP53—contribute to PDAC risk and may influence disease biology. This review provides an overview of the genetic landscape of hereditary and FPC, focusing on established cancer predisposition syndromes and emerging susceptibility genes. Current evidence regarding the prevalence, penetrance, and clinical relevance of germline pathogenic variants (PGVs) is summarized, together with the challenges associated with identifying individuals at increased risk. Contemporary recommendations for germline genetic testing, including the use of multigene panel approaches and limitations in real-world implementation, are also discussed. In addition, surveillance strategies for PDAC in high-risk individuals (HRI) are reviewed, and the available data on the outcomes and limitations of surveillance programs are examined. Finally, the therapeutic implications of inherited alterations, particularly in DNA repair-deficient PDAC, are outlined with reference to genotype-informed systemic treatment approaches. Full article

Early-onset colorectal cancer is increasing, making reproductive health an increasingly relevant survivorship issue. While immune checkpoint inhibitors have altered the management of deficient mismatch repair/microsatellite instability-high (dMMR/MSI-H) colorectal cancer, their implications for reproductive-age women remain insufficiently defined. We performed a focused narrative review, structured in line with the SANRA framework, to clarify this specific clinical domain. Immunotherapy may reshape female oncofertility counseling through two distinct mechanisms: direct reproductive uncertainty, including established endocrine toxicities and hypothesized, but currently unproven, direct gonadal effects; and indirect pathway-modifying effects, such as the potential avoidance of pelvic radiotherapy or radical surgery in selected patients with locally advanced dMMR/MSI-H rectal cancer. Anatomical organ preservation should not be automatically equated with functional fertility preservation. The key clinical message is that reproductive counseling should not be restricted to historically gonadotoxic chemotherapy. Instead, early multidisciplinary guidance should explicitly distinguish CRC-specific evidence from extrapolated or theoretical concerns, integrate fertility preservation strategies when clinically feasible, and address pelvic and sexual health, contraception, washout, endocrine follow-up, and future pregnancy planning. Until prospective CRC-specific reproductive data become available, immunotherapy should not be presented as either reproductively neutral or fertility-preserving. Full article

Pancreatic cancer remains one of the most aggressive and lethal malignancies, characterized by late-stage diagnosis, profound molecular heterogeneity, and limited responsiveness to conventional cytotoxic therapies. Recent advances in molecular diagnostics and biomarker-driven treatment stratification have accelerated the development of precision therapeutic approaches aimed at improving outcomes in selected patient populations. This review highlights three mechanistically distinct yet complementary therapeutic strategies that illustrate the evolving landscape of personalized pancreatic cancer management. Adagrasib represents targeted inhibition of oncogenic KRAS G12C signaling, reflecting recent progress in directly targeting historically “undruggable” driver mutations. Dostarlimab illustrates the tissue-agnostic application of immune checkpoint blockade in pancreatic cancers harboring mismatch repair deficiency (dMMR) or high microsatellite instability (MSI-H), highlighting the growing importance of biomarker-defined immunotherapy-responsive subsets despite the limited pancreatic cancer-specific clinical evidence currently available. Trastuzumab deruxtecan represents a next-generation HER2-directed antibody–drug conjugate (ADC) and demonstrates the potential of HER2-targeted therapy in the small subgroup of patients with HER2-positive pancreatic cancer, although the available evidence is derived primarily from basket trials and tumor-agnostic clinical development. Collectively, these therapeutic approaches underscore the expanding role of biomarker-guided treatment strategies integrating targeted inhibition, immunotherapy, and precision cytotoxic payload delivery. This review summarizes the molecular rationale, available clinical evidence, therapeutic limitations, and resistance mechanisms associated with these approaches while discussing emerging directions in translational research, rational combination strategies, liquid biopsy applications, and precision oncology that may further refine individualized treatment algorithms for pancreatic cancer. Full article

Background: Awake craniotomy is well established in adult neurosurgery for lesions near eloquent cortical areas, but its use in children remains uncommon and presents substantial anesthetic, psychological, and organizational challenges. We report the anesthesiologic management of awake craniotomy in a child with constitutional mismatch repair deficiency (CMMRD). Case Presentation: A 10-year-old boy with CMMRD underwent resection of a recurrent left frontal IDH-mutant astrocytoma, WHO grade 3, located adjacent to eloquent language cortex. Because of the high risk of postoperative language impairment, a structured multidisciplinary pathway was implemented, including neurosurgical, neuropsychological, and anesthesiologic evaluation, preoperative familiarization, and intraoperative language testing. An asleep–awake–asleep strategy was used. After induction with propofol, fentanyl, and rocuronium, the airway was secured with a supraglottic airway device (air-Q) followed by fiberoptic-guided tracheal intubation. During the awake phase, propofol was discontinued, remifentanil reduced, and low-dose dexmedetomidine introduced to preserve cooperation. The patient completed intraoperative language mapping, enabling identification of functional language boundaries and safe resection. No major intraoperative adverse events, airway complications, or seizures occurred. Postoperative pain scores remained below 4 on an age-appropriate Numeric Rating Scale, and the patient showed no new neurological deficits. At 1-month follow-up he remained symptom-free. Conclusions: This case adds to the still limited pediatric experience with awake craniotomy and suggests that, in carefully selected children managed within a structured multidisciplinary perioperative pathway and with a tailored anesthetic strategy, the procedure can be performed safely; confirmation in larger series is nonetheless required. Full article

The prognostic significance of next-generation sequencing (NGS) findings during the hormone-sensitive phase of prostate cancer remains incompletely characterized. This retrospective cohort study included 92 patients who underwent NGS analysis on tumor tissue between 2019 and 2025. The primary endpoint was time to castration-resistant prostate cancer (CRPC) from androgen deprivation therapy (ADT) initiation; secondary endpoints were overall survival from ADT initiation (OS-ADT) and from diagnosis. Kaplan-Meier and Cox regression analyses were performed. CRPC developed in 66 patients (71.7%) at a median of 21.1 months. The most frequently altered genes were ATR (35.9%), PTEN (28.3%), TP53 (26.1%), and BRCA2 (15.2%). KMT2C alteration (5.4%) was the strongest independent genomic predictor of shorter time to CRPC (HR = 6.804, p = 0.003) and OS-ADT (HR = 4.730, p = 0.019). TP53 alteration independently predicted shorter OS-ADT (HR = 1.810, p = 0.038). High genomic burden independently predicted shorter time to CRPC (HR = 1.917, p = 0.032). Homologous recombination repair deficiency was not associated with outcomes, attributable to high ATR alteration frequency introducing pathway heterogeneity. Mismatch repair deficiency showed a borderline association with shorter OS-ADT (20.7 vs. 44.0 months; p = 0.060). An exploratory composite risk score stratified patients into three prognostic groups with markedly different outcomes (HR = 7.904, p = 0.001). NGS analysis during the hormone-sensitive phase identifies independent predictors of castration resistance, supporting its integration at ADT initiation for risk stratification and biomarker-guided treatment planning. Full article

Mismatch repair–deficient (dMMR) or microsatellite instability-high (MSI-H) colorectal cancers exhibit high mutational burden and abundant neoantigen formation, generating a highly immunogenic tumour microenvironment characterised by dense lymphocytic infiltration and strong sensitivity to immune checkpoint inhibition. In metastatic colorectal cancer, PD-1 blockade produces durable responses almost exclusively in dMMR tumours, establishing mismatch repair status as a predictive biomarker for immunotherapy responsiveness. Recent studies extending immune checkpoint inhibitors (ICIs) into the neoadjuvant setting for localised dMMR colorectal cancer have produced major pathological response rates exceeding 90%, with pathological complete response (pCR) rates frequently surpassing 60%, challenging traditional oncologic staging frameworks, particularly with respect to lymph node assessment. Baseline clinical nodal staging in dMMR tumours is complicated by immune-mediated lymphadenopathy. Reactive lymphoid hyperplasia driven by tumour antigen exposure frequently produces enlarged lymph nodes that mimic metastatic disease on cross-sectional imaging. Following neoadjuvant immunotherapy, treatment-related immune activation may further increase nodal size or metabolic activity, while pathological examination often reveals sterilised nodes or immune infiltration without viable tumour. Consequently, conventional radiologic criteria for nodal metastasis demonstrate limited specificity in this context. The discordance between imaging findings and pathological outcomes raises important implications for staging accuracy, response assessment, and treatment planning. This review examines the biological basis of lymphatic involvement in dMMR colorectal cancer, evaluates the performance of current imaging modalities for nodal staging, and summarises emerging evidence from neoadjuvant immunotherapy trials. Particular emphasis is placed on the interpretation of lymph node findings in the era of immune checkpoint blockade and the implications for surgical decision-making, organ preservation, and future staging paradigms. Full article

Background/Objectives It is not established whether melanoma and lung cancer are part of the tumor spectrum of the Lynch syndromes (LS). Our first hypothesis was that, if melanoma is associated with LS, most prospectively observed cases would be carriers of pathogenic MSH2 variants (path_MSH2), as for other LS non-endodermal tumors. Our second hypothesis, which was derived from findings of the first study, was that the pattern of differences in the incidence of lung cancer in path_MMR carriers would mirror that for melanoma. Methods We used the Prospective Lynch Syndrome Database (PLSD) data and methods. Results Firstly, consistent with hypothesis, ten of 3154 path_MSH2 carriers followed for 26,309 years developed melanoma, compared with 6 of 5288 path_MLH1/MSH6/PMS2 carriers followed for 45,081 years (p = 0.04). Secondly, although the incidence of melanoma in carriers of path_MSH2 was 0.00041—similar to the populations in which the carriers resided—the average incidence rates for path_MLH1/MSH6/PMS2 carriers was 0.00012, lower than the corresponding population rates. Thirdly, the average lung cancer incidence rates in PLSD were 0.00112 in path_MSH2 carriers and 0.00032 in path_MLH1/MSH6/PMS2 carriers (p = 0.02), both lower than the population rates. Conclusions Melanomas and lung cancers—both of which are immunogenic through mechanisms independent of mismatch repair deficiency—may become even more immunogenic when they also exhibit microsatellite instability. This may lead to an increased likelihood that both tumors are eliminated by the immune system and, thus, show variable and lower incidence. These insights may help inform strategies for cancer prevention or treatment that are aimed at simultaneously interrupting multiple carcinogenic pathways. Full article

Introduction: Optimal systemic treatment for recurrent or advanced endometrial cancer (EC) remains uncertain, particularly in the second-line setting. While first-line chemotherapy with paclitaxel and carboplatin is widely used, its efficacy is limited. Recent evidence suggests that adding immune checkpoint inhibitors (ICIs) to chemotherapy (ChT) can improve progression-free survival (PFS). In addition, hormonal therapies (such as progestins and aromatase inhibitors), targeted therapies and ICIs used alone or in combination are emerging as potential treatment options. Objectives: Our objective was to systematically evaluate the efficacy and safety of systemic therapies beyond standard ChT for patients with recurrent or advanced EC, focusing on progression-free survival (PFS), overall survival (OS), and treatment-related adverse events (TRAEs). Methods: We conducted a systematic review and meta-analysis of randomized controlled trials (RCTs), prospective studies, and retrospective studies up to June 2024 on PubMed, Embase, and CENTRAL. Studies evaluating systemic therapies—chemotherapy, hormonal therapy, targeted agents, and ICIs—in recurrent or advanced EC were included. Primary outcomes were PFS and OS; secondary outcomes included grade ≥ 3 treatment-related adverse events. Risk of bias was assessed using the Cochrane RoB 2 and MINORS tools, and GRADE was applied to evaluate the certainty of evidence. Results: Five RCTs evaluated the addition of ICI to conventional ChT. In mismatch repair-deficient (MMRd) patients, the addition of ICI significantly improved PFS and OS compared to the ChT-only group. In mismatch repair-deficient (MMRd) patients, the median PFS (mPFS) was 8.39 months in the ChT group and 22.73 months in the ICI group (HR: 0.34, p < 0.001). OS results were 26.48 and 41.36 months, respectively. In mismatch repair-proficient (MMRp) patients, mPFS was 9.4 months in the ChT group and 10.18 months at the ICI group (HR: 0.72, p = 0.002). OS was 27.37 and 27.79 months, respectively. We conducted several exploratory single-arm subgroup analyses and multiple individual patient data (IPD) meta-analyses across several clinically relevant subgroups, including patients treated with progestins, lenvatinib plus pembrolizumab, PI3K/AKT/mTOR inhibitor monotherapy, and PI3K/AKT/mTOR inhibitors in combination with aromatase inhibitors. Detailed descriptive analyses were performed for each subgroup. Conclusions: Combining chemotherapy with ICIs appears to show the most favorable survival outcomes, especially in MMRd tumors. Taking into account the methodological limitations inherent in the elaboration of lower-level evidence and IPD, hormonal and targeted therapies might be considered viable options, with efficacy and safety profiles dependent on tumor biology. Better stratification of the EC patient cohort is warranted. Full article

Background/Objectives: The double-strand break repair protein MRE11 forms the core of the MRE11/RAD50/NBS1 (MRN) complex. Cancers with reduced MRE11 expression have been suggested to be more sensitive to radio-chemotherapy and may be subject to synthetic lethality. The aim of this study was to assess the prevalence of MRE11 deficiency and the potential role and clinical significance of elevated and/or reduced MRE11 expression in human cancer. Methods: A tissue microarray containing 14,966 samples from 134 different tumor entities was analyzed for MRE11 by immunohistochemistry. Results: In normal tissues, strong nuclear MRE11 staining occurred in almost all cell types. In cancers, nuclear MRE11 staining was strong in 11,797 (91.0%), moderate in 1018 (7.9%), weak in 86 (0.7%), and completely absent (MRE11 deficiency) in 55 (0.4%) of 12,956 informative tumor samples. Only six tumor entities had more than one MRE11-deficient cases including hepatocellular carcinoma (9 of 193), intestinal type gastric adenocarcinoma (4 of 208), endometrioid endometrial carcinoma (5 of 268), pulmonary adenocarcinoma (2 of 165), colorectal adenocarcinoma (CRC, 16 of 2183), and clear cell renal cell carcinoma (ccRCC, 7 of 1011). Reduced MRE11 staining was associated with mismatch repair deficiency (dMMR) in CRC and in gastric adenocarcinoma (p < 0.0001 each), advanced pT stage (p = 0.0003) and L1 status (p = 0.0019) in testicular seminoma, high grade (p < 0.05), advanced pT (p < 0.0001), and high UICC stage (p = 0.0014) in ccRCC, advanced pT stage in high-grade serous ovarian carcinoma (p = 0.0396), and nodal metastases in papillary thyroid cancer (p = 0.0332). Conclusions: MRE11 is highly expressed in most cancers. Reduced MRE11 expression is associated with aggressive phenotype in multiple cancer types. The potential to exploit MRE11 deficiency as a target for synthetic lethality deserves to be further explored. Full article

Background: Colorectal cancer (CRC) remains a leading cause of cancer-related mortality worldwide, with poor survival rates of late-stage disease. While immune checkpoint blockade (ICB) therapy has transformed treatment for mismatch repair-deficient (MMRd)/microsatellite instability-high (MSI-H) tumors, most CRC cases are mismatch repair-proficient (MMRp)/microsatellite-stable (MSS) and derive little to no benefit from current immunotherapy regimens. Tumor-associated macrophages (TAMs) constitute a significant component of the tumor microenvironment (TME) and exhibit a phenotypic gradient between pro-inflammatory (M1-like) and anti-inflammatory, immunosuppressive (M2-like) states. Although their polarization status is increasingly recognized as a key modulator of immunotherapy efficacy in CRC, a comprehensive synthesis of the literature regarding macrophage polarization and its relevance to improving CRC immunotherapy remains lacking. Methods: A systematic literature search was conducted across PubMed, EMBASE, and ScienceDirect from inception to December 2025 using terms encompassing macrophages, immunotherapy, immune checkpoint expression, colorectal cancer, and microsatellite stability status. Title, abstract, and full-text screening were performed independently by multiple authors. Sixty-five studies were included following PRISMA guidelines. The protocol was prospectively registered on PROSPERO (ID: CRD420251244320). Results: Three key themes were identified: (1) macrophage-mediated mechanisms of resistance to ICB, including M2 polarization driven by the PI3Kγ, STAT3, mTOR, and SIRT-1 axes, immunosuppressive cytokine production (IL-10, TGF-β), and altered immune checkpoint ligand expression; (2) macrophage polarization status and associated biomarkers as prognostic indicators of therapeutic response; (3) emerging macrophage-targeted therapeutic strategies in ongoing clinical trials, including CSF1R inhibitors, CD40 agonists, CD47/SIRPα blockade, and STING agonists. Conclusions: TAM polarization is a critical determinant of immunotherapy resistance and patient prognosis in CRC. Macrophage-targeted strategies, particularly M2-to-M1 repolarization approaches used in combination with existing ICB regimens, represent a promising avenue for expanding immunotherapy efficacy beyond MSI-H disease. Further translational research and randomized controlled trials are needed to validate these targets clinically. Full article

Background: Evidence suggests dMMR/MSI-H gastric cancer patients respond better to immune checkpoint inhibitors (ICIs) than to chemotherapy, but recent trials have not consistently shown this benefit in subgroup analyses. It remains unclear whether improved the pathological response translates into survival benefit. This study compares pathological response and survival outcomes between neoadjuvant immunotherapy regimens (ICI monotherapy, ICI plus chemotherapy, or dual ICIs; group A) and chemotherapy alone (group B) in locally advanced dMMR/MSI-H gastric cancer. Methods: Between January 2020 and December 2025, 24 patients undergoing surgery were enrolled—14 in group A and 10 in group B. The primary endpoints were major pathological response (MPR), pathological complete response (pCR), event-free survival (EFS), and overall survival (OS). A meta-analysis integrating our cohort with external studies was conducted to strengthen the evidence base. Results: In our cohort, compared with group B, group A appeared to have higher rates of MPR (85.7% vs. 20%) and pCR (42.9% vs. 0%). EFS and OS in group A improved numerically (EFS: p = 0.10; OS: p = 0.12). Surgical outcomes and treatment-related adverse events were not different between the two groups. Pooled analyses implied consistent improvements in MPR (RR = 4.09) and pCR (RR = 5.38). Additionally, reconstructed individual survival data suggested that group A might have better EFS (p = 0.034) while OS (p = 0.890) showed little difference. Conclusions: Neoadjuvant immunotherapy-based regimens might show some enhancements in treatment response rates and EFS compared with chemotherapy alone, which may imply their therapeutic potential in this molecularly defined patient population. Full article

Background: Microsatellite instability (MSI) and mismatch repair (MMR) deficiency are key predictive biomarkers for immune checkpoint inhibitors (ICIs) in metastatic colorectal cancer (mCRC). In real-world practice, however, diagnostic pathways often involve heterogeneous testing modalities, which may lead to discordant or inconclusive results. Methods: We conducted a retrospective study of patients with mCRC who underwent at least one MSI/MMR assessment between 2015 and 2025. Diagnostic modalities included IHC, tissue-based and liquid-based MSI testing. A predefined decision algorithm classified results as conclusive or inconclusive; discordant cases underwent adjudication that integrated a pathology review, molecular features, and technical considerations. Patients were ultimately assigned to definitive MSS or definitive MSI groups. Clinical characteristics, treatment patterns, and outcomes—particularly in relation to immunotherapy—were evaluated. Results: Among 727 evaluable patients, the MSI/MMR status was conclusive in 695 (95.6%) and inconclusive in 32 (4.4%). Inconclusive cases resulted from isolated MMR protein loss, heterogeneous or equivocal staining, inter-tumoral discordance, or discrepancies between tissue- and liquid-based assays. After adjudication, 54 patients (7.4%) were classified as definitive MSI and 673 (92.6%) as definitive MSS. Definitive MSI tumors were associated with female sex, right-sided primaries, high-grade histology, nodal involvement, and BRAF V600E mutations. Among the definitive MSI patients, 31 (57.4%) received immunotherapy, achieving a complete response rate of 48.4% and an overall response rate of 71.0%. Median PFS and OS were not reached in the definitive MSI group, whereas definitive MSS patients treated with ICIs experienced significantly poorer outcomes. Conclusive and adjudicated MSI groups demonstrated comparable responses to immunotherapy. Conclusions: In real-world practice, a meaningful proportion (4%) of mCRC patients experience inconclusive MSI/MMR assessment, with important clinical implications. Both technical and biological factors contribute to diagnostic uncertainty. Integrating orthogonal testing modalities and applying structured adjudication improves classification accuracy and ensures appropriate access to immunotherapy. Full article