High Microsatellite Instability Research Articles

Therapeutic Advances in Gastrointestinal Cancers: Immuno-oncology and Beyond

At the European Society for Medical Oncology (ESMO) Congress 2024 in Barcelona, Spain, the latest advancements in immunotherapy for colorectal cancer (CRC), gastro-oesophageal cancers, and hepatocellular carcinoma (HCC) were presented. Sara Lonardi from the Veneto Institute of Oncology, Italy, discussed the role of neoadjuvant immunotherapy in patients with high microsatellite instability (MSI-H) CRC, highlighting promising data from the CheckMate 8HW and NICHE-2 trials. Tania Fleitas Kanonnikoff from INCLIVA, Hospital Clínico Universitario de Valencia, Spain, provided insight into the use of immunotherapy-based regimens for gastro-oesophageal cancers, including treatment considerations based on key biomarkers and emerging treatment options. Thomas Decaens from the University of Grenoble-Alpes, France, presented results from several trials, including IMbrave150, HIMALAYA, and CheckMate 9DW, supporting the increasing role of immunotherapy combinations in first-line (1L) HCC treatment, which has been shown to improve overall survival in this challenging disease.

Case report: MSI-H, EGFR mutation, and ground-glass nodules as diffuse pulmonary hematogenous metastases

Ground-glass nodules (GGNs) are generally considered an early stage of lung cancer. The imaging characteristics and curative efficacy of multiple GGNs as metastases remain unclear. Microsatellite instability-high (MSI-H) is a biomarker for immunotherapy. The therapeutic effect and prognosis for patients with MSI-H and Epidermal Growth Factor Receptor (EGFR)-sensitive mutation stays uncertain. Here, we report a case of a lung adenocarcinoma patient presenting with ground-glass metastases, MSI-H, and EGFR-sensitive mutation and provide clinical data on the efficacy and prognosis. We describe the predictive significance of carcinoembryonic antigen (CEA) for disease progression when there is inconsistency between treatment effectiveness and CEA changes.

Extramammary Paget's disease treated with of anti-programmed cell death protein 1 therapy after docetaxel therapy failure.

Extramammary Paget's disease (EMPD) is a rare skin cancer with no standard treatment for advanced-stage disease. Although docetaxel-based chemotherapy is common, no standard treatment exists. Pembrolizumab is approved for solid tumors with a high tumor mutation burden (TMB) and/or high microsatellite instability, and nivolumab was approved in Japan in February 2024 for unresectable advanced or recurrent epithelial skin malignancies. However, there is a lack of real-world data regarding the efficacy of anti-programmed cell death protein 1 (PD-1) therapy for EMPD. We present the case details of three EMPD patients treated with anti-PD-1 therapy after docetaxel treatment, with TMB values of 17.8, 14.3, and 5.0 mut/Mb, respectively, and we review similar reported cases. Even in the cases with a high TMB, the response to anti-PD-1 therapy was not sufficient. Most cases involve second-line or later treatments, so further research is needed to determine the precise effectiveness of anti-PD-1 therapy as a first-line treatment.

Analysis of Clinicopathological and Molecular Features of Microcystic, Elongated, and Fragmented Pattern Invasion in Endometrioid Endometrial Cancer.

Background: Microcystic, elongated, and fragmented (MELF) invasion is a special invasion pattern in endometrioid endometrial cancer (EEC). This study aimed to investigate the clinical, pathological, and molecular features of the MELF pattern and its prognostic value in patients with EEC. Materials and Methods: The clinical and pathological data of 342 patients with EEC were retrospectively collected at Peking University People's Hospital from January 2019 to December 2022. Some key clinicopathological features were evaluated, including the tumor grade, Federation of Gynecology and Obstetrics (FIGO) staging, cervical stromal involvement, lymph node status, and lymphatic vascular space infiltration (LVSI). Immunohistochemical staining and molecular tests were performed, and the relevant literature was reviewed. Results: The MELF pattern was more prevalent in low-grade EEC. A significant correlation was found between the MELF pattern and advanced FIGO staging, LVSI, the depth of myometrial invasion, cervical stromal involvement, and lymph node metastasis (LNM). The incidence of mismatch-repair-deficient (MMRd) proteins was much higher in the MELF group than in the no-MELF group. Molecular testing revealed that, after copy number-low (CNL), microsatellite instability-high (MSI-H) was the second-most frequent subtype in the MELF group. The recurrence risk did not significantly differ between the MELF and no-MELF groups, but the differences among the four molecular subtypes were statistically significant. However, the MELF group experienced a shorter recurrence time. Among the four molecular subtypes, the recurrence risk was the highest in the CNH subgroup, followed by the MSI-H subgroup. Conclusions: MELF is a special invasion pattern in EEC and is associated with distinct clinicopathological and molecular characteristics, including the latest 2023 FIGO staging. Further research is warranted to explore its implications for treatment strategies and patient outcomes.

MSI-H Detection by ddPCR in Endoscopic Ultrasound Fine Needle Biopsy (EUS-FNB) from Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive disease with limited survival. Curative opportunities are only available for patients with resectable cancer. Palliative chemotherapy is the current standard of care for unresectable tumors. Numerous efforts have been made to investigate new therapeutic strategies for PDAC. Immunotherapy has been found to be effective in treating tumors with high microsatellite instability (MSI-H), including PDAC. The ability of the Endoscopic Ultrasound Fine Needle Biopsy (EUS-FNB) to reliably collect tissue could enhance new personalized treatment by permitting genomic alterations analysis. The aim of this study was to investigate the feasibility of obtaining adequate DNA for molecular analysis from EUS-FNB formalin-fixed-paraffin-embedded (FFPE) specimens. For this purpose, FFPE-DNA obtained from 43 PDAC archival samples was evaluated to verify adequacy in terms of quantity and quality and was tested to evaluate MSI-H status by droplet digital PCR (ddPCR). All samples were suitable for ddPCR analysis. Unlike the 1–2% MSI-H frequency found with traditional techniques, ddPCR detected this phenotype in 16.28% of cases. This study suggests the ddPCR ability to identify MSI-H phenotype, with the possibility of improving the selection of patients who may benefit from immunotherapy and who would be excluded by performing traditional diagnostic methods.

MSH6-proficient crypt foci in MSH6 constitutional mismatch repair deficiency: reversion of a frameshifted coding microsatellite to its wild-type sequence.

The discovery of "mismatch repair deficient (MMRd)-crypt foci" in non-neoplastic intestinal mucosa in Lynch syndrome (LS) has significantly enhanced our understanding of how tumors and tumor immunity form and evolve in LS. In this study, we report the frequent presence of "mismatch repair proficient (MMRp)-crypt foci" in both non-neoplastic and neoplastic intestinal mucosa in a patient with constitutional MMR deficiency (CMMRD), who carried a germline MSH6 pathogenic variant (c.3261dupC) in trans with an MSH6 likely pathogenic variant (c.3724_3726del) and whose tissues were otherwise deficient in MMR globally. The MMRp-crypts occurred at a rate of 1.1/100 crypts in non-neoplastic intestinal mucosa and were readily discernible in adenomas > 1cm. Sequencing analysis revealed normalization of the MSH6c.3261dupC variant in MMRp-adenoma crypts, indicating reverse frameshifting of the exon 5 C8 microsatellite. Interestingly but not surprisingly, the MMRp-adenoma crypts remained microsatellite-instability-high (MSI-H), and shared oncogenic APC mutations with the background MMRd-adenoma. Contrasting with MSH6-CMMRD, no PMS2-CMMRD individuals (0/5) harbored MMRp-crypts. In conclusion, our study documents distinct MMRp-crypts in MSH6-CMMRD, a phenomenon in keeping with MSH6 being a frequent target of MSI-H due to its coding microsatellite and suggesting that MSH6-CMMRD can potentially serve as a unique model system to further our understanding of MSH6's role in MSI-H tumor formation and evolution. Our findings also bear diagnostic implications; when using MMR immunohistochemistry as an ancillary tool in detecting CMMRD, awareness of these MMRp crypts can help avoid diagnostic pitfalls.

Clinicopathological Characteristics and Outcomes of Colorectal Cancer With Heterogenous Staining of Mismatch Repair Protein.

Scant data are available on heterogenous staining of mismatch repair protein in colorectal cancer. This study aimed to improve insights into clinicopathologic features and prognosis of colorectal cancer harboring heterogenous mismatch repair protein staining. A single-center retrospective observational study. This study was conducted in a tertiary referral center in China between 2014 and 2018. Colorectal cancers with heterogenous staining of mismatch repair protein were included. Clinicopathologic and molecular features, and survival outcomes were analyzed. A total of 151 out of 6721 colorectal cancers (2.2%) exhibited heterogenous staining for at least one mismatch repair protein, with intraglandular heterogeneity being the most common pattern (89.4%). Heterogenous MLH1 staining was significantly associated with distant metastasis (p = 0.03), while heterogenous MSH2 staining was associated with left-sided (p = 0.03) and earlier pT stage tumors (p = 0.02). The rates of microsatellite instability-high, KRAS and BRAF mutation were 12.6%, 47.3% and 3.4%, respectively. Microsatellite instability-high was significantly associated with higher intraglandular MSH6 heterogeneity frequency (p < 0.001) and decreased MSH6 expression level (< 27.5%, p = 0.01). BRAF mutation was associated with the coexistence of intraglandular and clonal heterogeneity (p = 0.003) and decreased PMS2 expression level (p = 0.01). Multivariable analysis revealed that progression-free survival was significantly associated with tumor stage (p = 0.003), stroma fraction (p = 0.004), and heterogenous PMS2 staining (p = 0.02). Overall survival was linked to tumor stage (p = 0.006) and BRAF mutation (p = 0.01). The limitations of this study include the absence of testing for MLH1 promoter methylation and mismatch repair gene mutations, its retrospective design, and insufficient data related to direct comparison with deficient mismatch repair and proficient mismatch repair colorectal cancer. Heterogenous mismatch repair protein staining in colorectal cancer exhibits distinct associations with tumor location, stage, microsatellite instability, BRAF mutation and prognosis. It is recommended to report MSH6 heterogeneity as it may indicate microsatellite instability-high. See Video Abstract.

Association between microsatellite instability status, clinicopathological features and mitochondrial DNA amplification in patients with colorectal cancer.

The relationship between BRAF-V600E mutations, mitochondrial DNA amplification and microsatellite instability-high (MSI-H) in colorectal cancer (CRC) has yet to be fully elucidated. The aim of the present study was to assess the association between the MSI status and BRAF-V600E gene mutations/clinicopathological features/mitochondrial DNA amplification in CRC. A non-interventional study analysis was performed using the clinicopathological features of 455 patients with CRC. Immunohistochemistry was used to evaluate four mismatch repair proteins (MutS homolog 2, MutS homolog 6, MutL homolog 1 and postmeiotic segregation increased 2), Ki-67 index, and programmed cell death protein 1 (PD-1) and programmed cell death-ligand 1 (PD-L1) expression. Additionally, PCR coupled with capillary electrophoresis were used to ascertain the MSI status. Moreover, amplification refractory mutation system-PCR was used to detect BRAF-V600E gene mutation and fluorescence in situ hybridization analysis was used to assess mitochondrial DNA. A total of 455 patients were divided into the MSI high (MSI-H) group (n=52) and microsatellite stability (MSS) group (n=403) based on their MSI status. Compared with the results of immunohistochemistry of four mismatch repair proteins, the consistency rate between mismatch repair protein deficiency and MSI was 94.23%. There were significant differences in PD-L1, primary tumor site, clinical stage, degree of differentiation, tumor size, lymph node metastasis and the occurrence of multiple primary tumors between the MSI-H group and MSS group (P<0.05 or P<0.001). However, there were no significant differences for sex, age, PD-1, Ki-67 expression and BRAF-V600E. The 24-60-month survival rate of the patients in the MSI-H group was significantly higher than that of those in the MSS group (P<0.05). Furthermore, the number of mitochondrial DNA was significantly amplified in the MSI-H group. In conclusion, the present study demonstrated that the combined detection of PD-L1 and MSI in patients with CRC can provide more accurate and effective guidance for personalized treatment.

SMARCA4 mutations and expression in lung adenocarcinoma: prognostic significance and impact on the immunotherapy response.

The switch/sucrose non-fermenting (SWI/SNF) complex family includes important chromatin-remodeling factors that are frequently mutated in lung adenocarcinoma (LUAD). However, the role of one family member, SMARCA4, in LUAD prognosis and immunotherapy sensitivity remains unclear. In the present study, 6745 LUAD samples from the cBioPortal database were used to analyze the relationships between SMARCA4 mutations and patient prognoses and clinical characteristics. Additionally, we examined the correlation between SMARCA4 mutations and prognosis in patients treated with immunotherapy using two immune-related datasets. SMARCA4 mutations and low expression were associated with shorter survival, and mutations were associated with a high tumor mutational burden and high microsatellite instability. SMARCA4 mutations were accompanied by KRAS, KEAP1, TP53 and STK11 mutations. No significant difference was observed in the immunotherapy response between patients with and without SMARCA4 mutations. When KRAS or STK11 mutations were present, immunotherapy effectiveness was poorer; however, when both SMARCA4 and TP53 mutations were present, immunotherapy was more effective. Furthermore, low SMARCA4 expression predicted a higher immunophenoscore, and SMARCA4 expression was correlated with certain immune microenvironment features. Taken together, our results suggest that SMARCA4 mutations and low expression might be associated with poor LUAD prognosis. Additionally, immunotherapy efficacy in patients with SMARCA4 mutations depended on the co-mutant genes. Thus, SMARCA4 could be an important factor to be considered for LUAD diagnosis and treatment.

CT45A1-mediated MLC2 (MYL9) phosphorylation promotes natural killer cell resistance and outer cell fate in a cell-in-cell structure, potentiating the progression of microsatellite instability-high colorectal cancer.

Patients with microsatellite instability-high (MSI-H) colorectal cancer (CRC) have high tumor mutation burden and tumor immunogenicity, exhibiting a higher response rate to immunotherapy and better survival. However, a portion of MSI-H CRC patients still experience adverse disease outcomes. We aimed to identify the tumor-autonomous regulators determining these heterogeneous clinical outcomes. The Cancer Genome Atlas (TCGA) dataset was used to identify regulators in MSI-H CRC patients with unfavorable outcomes. Stable CRC tumor clones expressing targeted regulators were established to evaluate migratory and stemness properties, immune cell vulnerability, and cell-in-cell (CIC) structure formation. RNA-sequencing (RNA-seq) was used to identify enriched biological pathways in stable CRC tumor clones. Clinicopathological characterization of formalin-fixed paraffin-embedded (FFPE) MSI-H CRC specimens was performed to explore the underlying mechanisms involved. We showed that cancer/testis antigen family 45 member A1 (CT45A1) expression was upregulated in MSI-H CRC patients with poor survival outcomes. CT45A1-expressing microsatellite stable (MSS) CRC cells showed enhanced migratory ability. However, CT45A1-expressing MSI-H CRC cells, but not MSS CRC cells, showed higher resistance to natural killer (NK) cell cytotoxicity and served as outer cells in homotypic CIC structures, preventing exogenous or therapeutic antibody access to inner CRCcells. Inactivating RHO-ROCK/MLCK-MLC2 signaling with small-molecule inhibitors or short-hairpin RNAs (shRNAs) targeting myosin light chain kinase (MYLK) abolished NK cell resistance and reduced the outer cell fate of CT45A1-expressing MSI-H CRC cells. In MSI-H CRC patients, CT45A1-positive tumors exhibited increased MLC2 phosphorylation, increased outer cell fate, and decreased survival. We demonstrated that CT45A1 potentiates the advanced progression of MSI-H CRC, and targeting MLC2 phosphorylation may enhance immunotherapy efficacy in CT45A1-positive MSI-H CRC patients.

Liver metastases and peritoneal metastases and response to checkpoint inhibitors in metastatic colorectal cancer with microsatellite instability.

There have been conflicting reports on the predictive impact of metastatic disease sites on the response to checkpoint inhibitors (CPI) in microsatellite instability (MSI) metastatic colorectal cancers (mCRC). Recent studies have highlighted peritoneal metastases, ascites, and liver metastases as possible indicators of resistance to CPI. We performed a detailed analysis of high microsatellite instability (MSI-H) mCRC treated with programmed cell death (PD-1) or PD-1/cytotoxic T-lymphocyte-associated protein 4 CPI in a single center. Overall response rate (ORR), progression-free survival (PFS), overall survival (OS), and stable disease but with complete pathological response upon resection (SDcPR) were analyzed by the presence of liver metastases, peritoneal metastases, or absence of either. The impact of number and size of liver metastases on clinical outcomes were also interrogated. Thirty-five patients with MSI mCRC were included in the analysis. Patients with peritoneal metastatic disease had lower ORR and shorter PFS compared to patients without liver and peritoneal metastases. Contrary to recent reports, ORR and ORR + SDcPR rates were high in patients with liver metastases, at 58% and 66%, respectively. In the liver metastases category, a better response rate was noted for patients with<5 lesions compared to patients with more than 5 lesions. Patients who responded had a higher median tumor mutation burden than patients with progressive disease. In MSI mCRC, no single clinical characteristic was sufficient to preclude CPI response. Peritoneal metastatic disease was associated with numerically lower ORR and shorter PFS. In contrast, liver metastases do not predict poor outcome.

Neoadjuvant immunotherapy for dMMR and pMMR colorectal cancers: therapeutic strategies and putative biomarkers of response.

Approximately 15% of locally advanced colorectal cancers (CRC) have DNA mismatch repair deficiency (dMMR), resulting in high microsatellite instability and a high tumour mutational burden. These cancers are frequently sensitive to therapy with immune-checkpoint inhibitors (ICIs) in the metastatic setting. This sensitivity seems to be even more pronounced in locally advanced disease, and organ preservation has become a realistic aim in ongoing clinical trials involving patients with dMMR rectal cancer. By contrast, metastatic CRCs with proficient DNA mismatch repair (pMMR) are generally resistant to ICIs, although a proportion of locally advanced pMMR tumours seem to have a high degree of sensitivity to ICIs. In this Review, we describe the current and emerging clinical evidence supporting the use of neoadjuvant ICIs in patients with dMMR and pMMR CRC, and the potential advantages (based on a biological rationale) of such an approach. We discuss how neoadjuvant 'window-of-opportunity' trials are being leveraged to progress biomarker discovery and we provide an overview of potential predictive biomarkers of response to ICIs, exploring the challenges faced when evaluating such biomarkers in biopsy-derived samples. Lastly, we describe how these discoveries might be used to drive a rational approach to trialling novel immunotherapeutic strategies in patients with pMMR CRC, with the ultimate aim of disease eradication and the generation of long-term immunosurveillance.

Abstract C010: Integrating germline and somatic data to resolve variants of uncertain significance (VUS) in colorectal cancer (CRC) patients who self-identified as Hispanic/Latino

Abstract Germline and somatic genetic testing have become cornerstones for assessing patient risk and tailoring cancer treatment, respectively, relying on the ability to distinguish pathogenic from benign variants. Typically, clinical reporting from these tests is conducted independently, serving distinct clinical objectives and audiences. However, integrating the underlying genomic data from both germline and somatic tests can enhance interpretative clarity, particularly in resolving variants of unknown significance (VUS) that lack sufficient evidence to determine pathogenicity. This ambiguity is especially problematic for non-White populations and those of non-European ancestry, where VUSs are disproportionately found, thereby limiting the scope of precision medicine and perpetuating health disparities. To assess the potential utility of an integrated model, we examined a prospective cohort of 88 self-identified Hispanic patients with colorectal cancer (CRC), performing both germline and somatic genomic analyses. We found that at least one germline VUS was identified in 44% (39/88) of participants, compared to a frequently reported rate of below 15%. By integrating tumor transcriptome data, mutational signatures, and copy number variations with traditional germline testing, we aimed to clarify VUSs and identify driver mutations. Integrating data modalities of the tumor transcriptome, mutational signatures, and copy number variations alongside traditional germline testing can help clarify VUSs and identify driver mutations. We constructed a model whereby the assessment of VUSs was based on the putative functional impact on either the DNA mutational patterns or allelic expression observed in tumor RNA. Using our integrated model, we deemed the oncogene AXIN2 VUS of one participant was likely biologically significant due to mutant-allele specific expression observed in the tumor RNA. Furthermore, we showed that 26% (10/39) of participants harbored a VUS that was very likely benign based on the tumor mutational profile and RNA expression. These included variants associated with homologous recombination in PALB2 and BRCA2 as well as genes associated with DNA repair like MLH1, PMS2, POLE and POLD1. Among patients with VUSs in genes associated with homologous recombination deficiency (HRD), none exhibited HRD via copy number analyses. Conversely, of the six patients that did exhibit HRD, only one had a pathogenic variant in a gene associated with HRD (ATM). Additionally, we identified tumors with a DNA mismatch repair deficiency phenotype (high tumor mutational burden, high microsatellite instability, DNA mismatch repair deficiency mutational signature) but without a pathogenic variant in a Lynch syndrome-associated gene. Methylation analysis revealed hypermethylation of the MLH1 promoter in these cases, explaining the tumor phenotype. This finding indicates that our integrative method can accurately predict DNA mismatch repair deficiency even without a genetic alteration in a DNA mismatch repair gene. Citation Format: Jonathan Amzaleg, Julie O. Culve, Charité N. Ricker, Natalia Gutierrez, Yuxin Jin, Brigette Waldrup, Carmen Chaves, Lucia Enriquez, Joel Sanchez-Mendez, Daisy Hernandez, Bodour Salhia, Lourdes Baezconde-Garbanati, Mariana C. Stern, Enrique Velazquez Villarreal, John D. Carpten, Heinz-Joseph Lenz, David W. Craig. Integrating germline and somatic data to resolve variants of uncertain significance (VUS) in colorectal cancer (CRC) patients who self-identified as Hispanic/Latino [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr C010.

Abstract C165: Interrogating the Tumor and Immune Microenvironment of Endometrial Cancers Among a Diverse Cohort of Cases

Abstract Endometrial cancer (EC) is the sixth most common gynecological malignancy, with an increasing incidence worldwide over the last two decades. African American women are more likely to be diagnosed with endometrial cancer than Caucasian women. Unfortunately, African American women are more frequently diagnosed with high-grade EC, which occurs 2-3 times more often compared to their white and Hispanic counterparts. Additionally, African American women have higher mortality rates from EC than Caucasian women, highlighting a significant cancer disparity among these patients. Uterine EC disparities are induced by complex ecosystems composed of cellular niches with distinct genotypes, phenotypes, and spatial transcriptomic landscapes. In estrogen-dependent EC tumorigenesis, the endometrium undergoes uncontrollable proliferation, progressing from normal to atypical hyperplasia and ultimately to carcinoma. The heterogeneity of EC tumors complicates therapeutic targeting, rendering EC a challenging disease to cure. This study aims to investigate the genetic and transcriptomic features found in the tumor microenvironment of African American patients with EC. Previous research has shown that the molecular classification of EC tumors can be categorized as estrogen-driven, hypermutant, microsatellite instable, or lacking a specific molecular profile. Current models do not adequately reflect the oncogenic origin and pathological progression in patients. The cohort of EC cases includes primary, metastatic, and normal tumor tissues classified as Uterine Endometrial Adenocarcinoma, along with two Serous Papillary cases with varying tumor grades (low to high grade). Spatial transcriptomics and whole exome sequencing were performed on these samples. Spatial transcriptomics will identify the alterations in gene expression and the spatial landscape of the cell neighborhoods driving tumor heterogeneity. Whole exome sequencing will provide insight into the germline and somatic variants present in EC, offering a deeper understanding of the potential genetic drivers in African American patients. The genes expressed across the EC tumor landscape are implicated in cell proliferation, epithelial- mesenchymal transition, DNA damage response, and immune response. The analysis will also show the transition of normal to malignant endometrium harboring high tumor mutational burden and microsatellite instability when comparing paired samples. This comprehensive approach aims to elucidate the genetic and transcriptomic underpinnings contributing to the disparities observed in African American patients with EC, ultimately informing better-targeted therapies and improving outcomes. Citation Format: Danyelle Paine, John Carpten. Interrogating the Tumor and Immune Microenvironment of Endometrial Cancers Among a Diverse Cohort of Cases [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr C165.

Duration of immunotherapy in dMMR/MSI-H metastatic colorectal cancer patients

BackgroundImmune checkpoint blockade (ICB) has revolutionized treatment of mismatch repair-deficient (dMMR)/microsatellite instability-high (MSI-H) metastatic colorectal cancer (mCRC). However, there is no evidence on the optimal treatment duration. We aimed to compare outcomes of different immunotherapy durations. MethodsAn international multicenter retrospective cohort study of immunotherapy-naïve dMMR/MSI-H mCRC patients who received immunotherapy between 2014–2024. Fixed treatment duration of two years was compared to treatment duration beyond two years. Fixed treatment duration of one year was compared to treatment duration beyond one year. Subgroup analysis was performed for patients who experienced CR. Kaplan-Meier analysis and Cox proportional hazard regression model were used to analyze the effect of all exposure variables on OS. ResultsThe study cohort included 757 dMMR/MSI-H mCRC patients treated with ICB. Median follow-up time was 46.7 months (IQR 28.5–70.3). There was no statistically significant difference in OS between patients treated for a two-year fixed-duration (n = 83) and those treated beyond two years (n = 139) in both the univariable and multivariable analysis (HR=0.65 95 %CI 0.14–3.07 p = 0.59 and HR=0.61 95 %CI 0.12–3.10 p = 0.6, respectively). The comparison between one-year fixed-duration versus continuing treatment beyond one year included 27 and 330 patients, respectively. For patients who achieved CR, discontinuing treatment after one year was not associated with a negative impact on OS (p = 0.5). ConclusionsDiscontinuing immunotherapy after two years is a reasonable option for dMMR/MSI-H mCRC patients with ongoing response. Treatment discontinuation after one year may be considered for patients achieving CR. Further prospective studies are needed to define the most appropriate duration of therapy.

High levels of tumor cell-intrinsic STING signaling are associated with increased infiltration of CD8+ T cells in dMMR/MSI-H gastric cancer

Mismatch repair deficient (dMMR)/microsatellite instability-high (MSI-H) gastric cancer (GC) exhibits an immune-active tumor microenvironment (TME) compared to MMR proficient (pMMR)/microsatellite stable/Epstein-Barr virus-negative [EBV (−)] GC. The tumor cell-intrinsic cyclic GMP–AMP synthase (cGAS)–stimulator of interferon genes (STING) pathway has been considered a key regulator of immune cell activation in the TME. However, its significance in regulating the immune-active TME in dMMR/MSI-H GC remains unclear. Here, we demonstrated that tumor cell-intrinsic cGAS–STING was highly expressed in dMMR GC compared to pMMR/EBV (−) GC. The expression of tumor cell-intrinsic STING was significantly and positively associated with the number of CD8+ tumor-infiltrating lymphocytes in GC. Analysis of TCGA datasets revealed that the expression of interferon-stimulated genes and STING downstream T-cell attracting chemokines was significantly higher in MSI-H GC compared to other subtypes of GC with EBV (−). These results suggest that tumor cell-intrinsic STING signaling plays a key role in activating immune cells in the dMMR/MSI-H GC TME and might serve as a novel biomarker predicting the efficacy of immunotherapy for GC treatment.

Immune microenvironmental heterogeneity according to tumor DNA methylation phenotypes in microsatellite instability-high colorectal cancers

The detailed association between tumor DNA methylation, including CpG island methylation, and tumor immunity is poorly understood. CpG island methylator phenotype (CIMP) is observed typically in sporadic colorectal cancers (CRCs) with microsatellite instability-high (MSI-H). Here, we investigated the differential features of the tumor immune microenvironment according to CIMP status in MSI-H CRCs. CIMP-high (CIMP-H) or CIMP-low/negative (CIMP-L/0) status was determined using MethyLight assay in 133 MSI-H CRCs. All MSI-H CRCs were subjected to digital pathology-based quantification of CD3 + /CD8 + /CD4 + /FoxP3 + /CD68 + /CD204 + /CD177 + tumor-infiltrating immune cells using whole-slide immunohistochemistry. Programmed death-ligand 1 (PD-L1) immunohistochemistry was evaluated using the tumor proportion score (TPS) and combined positive score (CPS). Representative cases were analyzed using whole-exome and RNA-sequencing. In 133 MSI-H CRCs, significantly higher densities of CD8 + tumor-infiltrating lymphocytes (TILs) were observed in CIMP-H tumors compared with CIMP-L/0 tumors. PD-L1 TPS and CPS in CIMP-H tumors were higher than in CIMP-L/0 tumors. Next-generation sequencing revealed that, compared with CIMP-L/0 tumors, CIMP-H tumors had higher fractions of CD8 + T cells/cytotoxic lymphocytes, higher cytolytic activity scores, and activated immune-mediated cell killing pathways. In contrast to CIMP-L/0 tumors, most CIMP-H tumors were identified as consensus molecular subtype 1, an immunogenic transcriptomic subtype of CRC. However, there were no differences in tumor mutational burden (TMB) between CIMP-H and CIMP-L/0 tumors in MSI-H CRCs. In conclusion, CIMP-H is associated with abundant cytotoxic CD8 + TILs and PD-L1 overexpression independent of TMB in MSI-H CRCs, suggesting that CIMP-H tumors represent a typical immune-hot subtype and are optimal candidates for immunotherapy in MSI-H tumors.

A phase II clinical trial of toripalimab in advanced solid tumors with polymerase epsilon/polymerase delta (POLE/POLD1) mutation

Patients carrying mutations in polymerase epsilon/polymerase delta have shown positive responses to immune checkpoint inhibitors. Yet, prospective trials exploring the efficacy in those with polymerase epsilon/polymerase delta mutations are still lacking. A phase II clinical trial was initiated to evaluate the efficacy of toripalimab, a humanized IgG4K monoclonal antibody to human PD-1, in patients with advanced solid tumors with unselected polymerase epsilon/polymerase delta mutations but without microsatellite instability-high. A total of 15 patients were enrolled, 14 of whom were assessed for treatment efficacy. There was a 21.4% overall response rate, with a disease control rate of 57.1%. The median overall survival and median progression-free survival were 17.9 (95% CI 13.5-not reach) months and 2.5 (95% CI 1.4-not reach) months, respectively. For patients with exonuclease domain mutations, the objective response rate was 66.7% (2/3), with a disease control rate of 66.7% (2/3). For those with non-exonuclease domain mutations, the rates were 9.1% (1/11) and 54.5% (6/11), respectively. Notably, patients with PBRM1 gene mutations exhibited a high response rate to toripalimab at 75.0% (3/4). This study showed that neither the exonuclease domain mutations nor non-exonuclease domain mutations could fully predict the efficacy of immunotherapy, urging the need for more investigations to clarify potential immune sensitization differences within polymerase epsilon/polymerase delta mutation variants.

Microsatellite Instability-High and High Tumor Mutation Burden Frequencies in Urologic Malignancies Off-Label for Immune Checkpoint Inhibitors in Japan: A Retrospective Single-Institutional Cohort.

Objectives Microsatellite instability-high (MSI-H) and high tumor mutation burden (TMB-high) frequencies were investigated to determine the efficacy and adverse events of pembrolizumab in patients with urologic malignancies (or their equivalents) for which immune checkpoint inhibitors (ICIs) are not covered by Japanese insurance. Methods Between February 2019 and April 2024, patients with urologic malignancies (or their equivalents) treated in our department for whom ICIs were not approved by Japanese insurance were screened with an MSI companion diagnostic kit or comprehensive genomic profiling (CGP). The efficacy of pembrolizumab therapy, presence of adverse events, and outcomes were evaluated retrospectively in patients with MSI-H or TMB-high. Results In total, 44 patients were tested, and the median age at testing was 70 years. Castration-resistant prostate cancer (CRPC) was the most common (n = 31). Overall, 49 tests were performed, including 22 MSI companion diagnostic kits and 27 CGP tests. Of the 49 tests, 1 detected MSI-H, 2 detected TMB-high, and 1 detected simultaneous MSI-H/TMB-high, with detection rates of 4.1% and 11.1% for MSI-H and TMB-high, respectively. A patient with MSI-H CRPC and neuroendocrine differentiation achieved a complete response and a prolonged duration of response to pembrolizumab without adverse events. The duration of response to pembrolizumab was shorter ina patient with TMB-high, and a CRPC patient with simultaneously detected MSI-H/TMB-high had to discontinue pembrolizumab early due to immune-related adverse events. Conclusions Despite the potential benefit of pembrolizumab, MSI-H or TMB-high was less frequently detected in urologic malignancies for which ICIs are not covered by Japanese insurance.

544P Nivolumab plus ipilimumab in microsatellite instability high (MSI)/mismatch repair-deficient (dMMR) metastatic colorectal cancer (mCRC): Final survival analysis and prognostic evaluation of GDF-15 in the phase II GERCOR NIPICOL study

544P Nivolumab plus ipilimumab in microsatellite instability high (MSI)/mismatch repair-deficient (dMMR) metastatic colorectal cancer (mCRC): Final survival analysis and prognostic evaluation of GDF-15 in the phase II GERCOR NIPICOL study