Microsatellite Instability-high Colorectal Cancer Research Articles

Real-World Treatment Patterns and Clinical Outcomes for Standard of Care Regimens in Patients with Deficient MMR or MSI-High Metastatic Colorectal and Non-Colorectal Cancer: A Retrospective Chart Review Study in France.

There is limited evidence on the effectiveness of standard of care (SOC) treatments in previously treated patients with deficient mismatch repair (dMMR) or microsatellite instability high (MSI-H) metastatic cancer. Immune checkpoints inhibitors (ICIs) have emerged as key treatments for dMMR/MSI-H tumors. However, clinical outcomes data with SOC regimens are still limited. Study objectives were to evaluate real-world treatment patterns and clinical outcomes in patients with dMMR/MSI-H metastatic colorectal cancer (mCRC) and non-CRC receiving SOC regimens. Given the resulting small cohort of patients with metastatic non-CRC, only summary results are provided. Two French university hospitals participated in a retrospective chart review study in which adult patients with dMMR/MSI-H mCRC and non-CRC were enrolled. Treatment patterns, overall survival (OS) from the start of third-line (3L, for mCRC) or second-line (2L, for non-CRC) treatment, and the best overall response rate (BORR) were reported. Thirty-six patients with dMMR/MSI-H mCRC were included. Almost all patients received combination treatments both in first-line (1L, 100%) and 2L (97%). For 3L and later, combination treatment was preferred over monotherapy but decreased in usage (75% at 3L and 57% at fourth-line, 4L). The BORR was 5.7% and median OS for patients with dMMR/MSI-H mCRC receiving 3L therapy was 9.0months (95% confidence interval, CI 4.0-14.1); it decreased to 4.1months (95% CI 4.0-9.0) when survival data of patients receiving ICIs at fourth or later lines were censored at progression date of prior treatment line. Real-world clinical outcomes observed for patients with dMMR/MSI-H mCRC receiving 3L treatment(s) are suboptimal, suggesting a high unmet need that could be addressed with ICIs.

Histopathologic and Molecular Biomarkers of PD-1/PD-L1 Inhibitor Treatment Response among Patients with Microsatellite Instability‒High Colon Cancer

PurposeRecent clinical trials have reported response rates < 50% among patients treated with programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) inhibitors for microsatellite instability–high (MSI-H) colorectal cancer (CRC), and factors predicting treatment response have not been fully identified. This study aimed to identify potential biomarkers of PD-1/PD-L1 inhibitor treatment response among patients with MSI-H CRC.Materials and MethodsMSI-H CRC patients enrolled in three clinical trials of PD-1/PD-L1 blockade at Asan Medical Center (Seoul, Republic of Korea) were screened and classified into two groups according to treatment response. Their histopathologic features and expression of 730 immune-related genes from the NanoString platform were evaluated, and a machine learning–based classification model was built to predict treatment response among MSI-H CRCs patients.ResultsA total of 27 patients (15 responders, 12 non-responders) were included. A high degree of lymphocytic/neutrophilic infiltration and an expansile tumor border were associated with treatment response and prolonged progression-free survival (PFS), while mucinous/signet-ring cell carcinoma was associated with a lack of treatment response and short PFS. Gene expression profiles revealed that the interferon-γ response pathway was enriched in the responder group. Of the top eight differentially expressed immune-related genes, PRAME had the highest fold change in the responder group. Higher expression of PRAME was independently associated with better PFS along with histologic subtypes in the multivariate analysis. The classification model using these genes showed good performance for predicting treatment response.ConclusionWe identified histologic and immune-related gene expression characteristics associated with treatment response in MSI-H CRC, which may contribute to optimal patient stratification.

Genomic and Transcriptomic Analysis of Microsatellite Instability-High Colorectal Cancer Patients with Targetable Alterations Identifies Clinical Implications for Immunotherapy

Genomic and Transcriptomic Analysis of Microsatellite Instability-High Colorectal Cancer Patients with Targetable Alterations Identifies Clinical Implications for Immunotherapy

Genomic and transcriptomic characterization of heterogeneous immune subgroups of microsatellite instability-high colorectal cancers

BackgroundColorectal cancers (CRCs) with microsatellite instability-high (MSI-H) are hypermutated tumors and are generally regarded as immunogenic. However, their heterogeneous immune responses and underlying molecular characteristics remain largely unexplained.MethodsWe conducted a...

Neoadjuvant PD-1 blockade with toripalimab, with or without celecoxib, in mismatch repair-deficient or microsatellite instability-high, locally advanced, colorectal cancer (PICC): a single-centre, parallel-group, non-comparative, randomised, phase 2 trial

PD-1 blockade is highly effective in patients with mismatch repair-deficient or microsatellite instability-high metastatic colorectal cancer. The role of single-agent PD-1 blockade in the neoadjuvant setting for resectable mismatch repair-deficient or microsatellite instability-high colorectal cancer remains unclear. We investigated the efficacy and safety of PD-1 blockade with toripalimab, with or without the COX-2 inhibitor celecoxib, as neoadjuvant treatment for mismatch repair-deficient or microsatellite instability-high, locally advanced, colorectal cancers. The PD-1 Inhibitor in Microsatellite Instability Colorectal Cancer (PICC) trial was a single-centre, open-label, parallel-group, non-comparative, randomised, phase 2 study undertaken at the Sixth Affiliated Hospital of Sun Yat-sen University (Guangzhou, China). Eligible patients were aged 18-75 years, had histologically confirmed mismatch repair-deficient or microsatellite instability-high colorectal cancer, had clinical stage T3-T4 or any T with lymph node positivity (N+), Eastern Cooperative Oncology Group performance score of 0 or 1, and adequate haematological, hepatic, and renal function. Participants were randomly assigned (1:1), without any stratification or balanced blocking, to receive toripalimab 3 mg/kg intravenously on day 1, with or without celecoxib 200 mg orally twice daily from day 1 to 14 of each 14-day cycle, for six cycles before surgical resection. Adjuvant treatment with toripalimab with or without celecoxib was permitted at the investigators' discretion. The primary endpoint was the proportion of patients with pathological complete response, defined as tumours without any viable tumour cells in the resected primary tumour sample and all sampled regional lymph nodes. All efficacy and safety analyses were assessed in the modified intention-to-treat population, which included all patients who were randomly assigned to treatment and who received at least one dose of toripalimab. This trial is registered with ClinicalTrials.gov, NCT03926338, and is ongoing. Between May 1, 2019, and April 1, 2021, 53 patients were screened, of whom 34 were randomly assigned to either the toripalimab plus celecoxib group (n=17) or the toripalimab monotherapy group (n=17). As of data cutoff (Aug 10, 2021), median follow-up was 14·9 months (IQR 8·8-17·0). All patients received study treatment and underwent surgical resection; there were no treatment-related surgical delays. All 34 patients had an R0 resection (>1 mm resection margin). 15 of 17 patients (88% [95% CI 64-99]) in the toripalimab plus celecoxib group and 11 of 17 patients (65% [38-86]) in the toripalimab monotherapy group had a pathological complete response. All patients continued to receive adjuvant toripalimab with or without celecoxib for a total perioperative duration of 6 months and were alive and free of recurrence at data cutoff. During neoadjuvant treatment, ten (59%) patients in the toripalimab plus celecoxib group and ten (59%) in the toripalimab monotherapy group had grade 1-2 treatment-related adverse events. Only one (3%) of 34 patients, who was in the toripalimab plus celecoxib group, had a grade 3 or higher treatment-related adverse event during the neoadjuvant phase, which was grade 3 increased aspartate aminotransferase levels. In the adjuvant phase, only one (3%) of 34 patients, who was in the toripalimab monotherapy group, had a grade 3 or higher treatment-related adverse events, which was grade 3 increased aspartate aminotransferase and alanine aminotransferase levels. Neoadjuvant toripalimab with or without celecoxib could be a potential therapeutic option for patients with mismatch repair deficient or microsatellite instability-high, locally advanced, colorectal cancer. This treatment was associated with a high pathological complete response rate and an acceptable safety profile, which did not compromise surgery. Longer term follow-up is needed to assess effects on survival-related endpoints. The National Key R&D Program of China, the National Natural Science Foundation of China, and the Chinese Society of Clinical Oncology-Junshi Biosciences Oncology Immunity Research. For the Chinese translation of the abstract see Supplementary Materials section.

HLA Class I Analysis Provides Insight Into the Genetic and Epigenetic Background of Immune Evasion in Colorectal Cancer With High Microsatellite Instability

A detailed understanding of antitumor immunity is essential for optimal cancer immune therapy. Although defective mutations in the B2M and HLA-ABC genes, which encode molecules essential for antigen presentation, have been reported in several studies, the effects of these defects on tumor immunity have not been quantitatively evaluated. Mutations in HLA-ABC genes were analyzed in 114 microsatellite instability-high colorectal cancers using a long-read sequencer. The data were further analyzed in combination with whole-exome sequencing, transcriptome sequencing, DNA methylation array, and immunohistochemistry data. We detected 101 truncating mutations in 57 tumors (50%) and loss of 61 alleles in 21 tumors (18%). Based on the integrated analysis that enabled the immunologic subclassification of microsatellite instability-high colorectal cancers, we identified a subtype of tumors in which lymphocyte infiltration was reduced, partly due to reduced expression of HLA-ABC genes in the absence of apparent genetic alterations. Survival time of patients with such tumors was shorter than in patients with other tumor types. Paradoxically, tumor mutation burden was highest in the subtype, suggesting that the immunogenic effect of accumulating mutations was counterbalanced by mutations that weakened immunoreactivity. Various genetic and epigenetic alterations, including frameshift mutations in RFX5 and promoter methylation of PSMB8 and HLA-A, converged on reduced expression of HLA-ABC genes. Our detailed immunogenomic analysis providesinformation that will facilitate the improvement and development of cancer immunotherapy.

Microsatellite instability-high colorectal cancer patient-derived xenograft models for cancer immunity research.

There is an increasing demand for appropriate preclinical mice models for evaluating the efficacy of cancer immunotherapies. Therefore, we established a humanized patient-derived xenograft (PDX) model using microsatellite instability-high (MSI-H) colorectal cancer (CRC) tissues and patient-derived peripheral blood mononuclear cells (PBMCs). The CRC tissues of patients scheduled for surgery were tested for MSI status, and CRC tumors were transplanted into NOD/LtSz-scid/IL-2Rg-/-(NSG) mice to establish MSI-H PDX models. PDX tumors were compared to the original patient tumors in terms of histological and genetic characteristics. To humanize the immune system of MSI-H PDX models, patient PBMCs were injected through the tail vein. PDX models were established from two patients with MSI-H CRC; one patient had a germline mutation in MLH1 (c.1990-2A > G), and the other patient had MLH1 promoter hypermethylation. PDX with the germline mutation was histologically similar to the patient tumor, and retained the genetic characteristics, including MSI-H, deficient mismatch repair (dMMR), and MLH1 mutation. In contrast, the histological features of the other PDX from a tumor with MLH1 promoter hypermethylation were clearly different from those of the original tumor, and MLH1 promoter hypermethylation and MSI-H/dMMR were lost in the PDX. When T cells from the same patient with MLH1 mutation were injected into the PDX through the tail vein, they were detected in the PDX tumor. The MSI-H tumor with an MMR mutation is suitable for MSI-H PDX model generation. The PBMC humanized MSI-H PDX has the potential to be used as an efficient model for cancer immunotherapy research.

Construction of a metastasis prediction model of microsatellite instability-high colorectal cancer based on differentially expressed gene assembly

Construction of a metastasis prediction model of microsatellite instability-high colorectal cancer based on differentially expressed gene assembly

ASO Visual Abstract: ATMIN Suppresses Metastasis by Altering the WNT Signaling Pathway via PARP1 in MSI-High Colorectal Cancer

ASO Visual Abstract: ATMIN Suppresses Metastasis by Altering the WNT Signaling Pathway via PARP1 in MSI-High Colorectal Cancer

Development of a liquid biopsy based purely quantitative digital droplet PCR assay for detection of MLH1 promoter methylation in colorectal cancer patients

BackgroundMutL Homolog 1 (MLH1) promotor methylation is associated with microsatellite instability high colorectal cancer (CRC). The strong correlation between methylation status and cancer development and progression has led to a growing interest in the use of methylation markers in circulating tumor DNA (ctDNA) for early cancer detection and longitudinal monitoring. As cancer-specific DNA methylation changes in body fluids are limited, it is particularly challenging to develop clinically applicable liquid biopsy methodologies with high sensitivity and specificity. The purpose of this study was to develop a fit-for-purpose methylation sensitive restriction enzyme (MSRE) based digital droplet PCR (ddPCR) assay to examine MLH1 promoter methylation in ctDNA in advanced CRC.MethodsPrimers and probes were designed to amplify CpG sites of the MLH1 promoter. Methylated and unmethylated control genomic DNA were sheared to mimic ctDNA and subjected to MSRE HpaII digestion. Plasma samples from 20 healthy donors and 28 CRC patients were analyzed with the optimized MSRE procedure using ddPCR.ResultsUsing methylated and unmethylated controls, we optimized the conditions for HpaII enzyme digestion to ensure complete digestion and avoid false positives. Based on the results from the ddPCR assay using 1 ng circulating cell-free DNA (cfDNA) input from healthy donors or CRC samples, ROC curves were generated with an area under the curve (AUC) value of 0.965 (95% CI: 0.94, 0.99). The statistically optimal assay sensitivity and specificity was achieved when 8 positive droplets were used as acceptance criteria (78% sensitivity and 100% specificity, 95% CI: 0.45, 0.95). A tiered-based cutoff (20, 50, 80% percentile based) was applied to distinguish CRC samples with different methylation level.ConclusionsOur study demonstrated that the liquid biopsy assay for MLH1 promoter methylation detection using purely quantitative ddPCR is a simple and highly sensitive procedure that provides reliable methylation detection in ctDNA. The MSRE ddPCR approach can also be applied to other genes of interest where methylation patterns could reveal clinically relevant information for future clinical biomarker and/or companion diagnostic development.

Abstract 1190: The enrichment of CD8+ T cell in TP53 pathway wild-type microsatellite stable colorectal cancer

Abstract Background: Colorectal cancer (CRC) patients with microsatellite instability-high (MSI-H) may respond to immune checkpoint inhibition (ICI), whereas CRC patients with microsatellite-stable (MSS) have not demonstrated response. However, a proportion of MSS tumors with increased immunogenicity may benefit from ICI therapy. We aim to identify these patients by analyzing the correlation between the three major pathways variation status and immune cell infiltration levels in CRC. Methods: Tumor tissues from 59 CRC patients were collected. Tumor immune microenvironment (TIME) was evaluated by multiple fluorescent immunohistochemical staining, somatic variations and microsatellite status were tested by next-generation sequencing (NGS). TIME includes antibodies of CD8+T cells, tumor associated macrophage M1/M2, and CD56bright and CD56dim NK cells. TP53, RTK-RAS, and WNT pathways were defined as mutation if mutations were tested in any genes in the corresponding pathway. Notably, TP53 pathway was composed of TP53 and ATM. The validation cohort was comprised of 266 Stage-III/IV TCGA-CRC patients whose immune cell infiltration levels were estimated by xCell (https://xcell.ucsf.edu/). Results: The 59 CRC patients were classified into two groups: MSI-H (n=11) and MSS(n=48), while the latter was further classified into TP53 mutant (n=44) and TP53 wild-type (n=4) groups according to TP53 pathway mutation status. The infiltration level of CD8+T cells were significantly lower in TP53 mutant MSS group than that of TP53 wild-type MSS (p value: 0.03) and MSI-H groups (p value: 0.01). Median CD8+T cells counts in TP53 mutant MSS, TP53 wild-type MSS, and MSI-H, groups were 87, 293, and 271 per square millimeter. While the infiltration level of tumor associated macrophage M1/M2, CD56bright and CD56dim NK cells were similar among the three groups. Besides, no significant difference of any immune cells was detected between RTK-RAS pathway mutant and wild-type MSS patients, and between WNT pathway mutant and wild-type MSS patients. The higher infiltration of CD8+T cells in TP53 wild-type MSS patients was further validated in TCGA-CRC cohort. Though no significant difference of CD8+T cells density was observed between TP53 wild-type MSS and TP53 mutant MSS in overall cohort, in those whose tumor located on the right colon (n=58), the infiltration level of central memory CD8+T cells (CD8+Tcm) was significantly lower in TP53 mutant MSS group (n=22) than that in MSI-H group (n=12, p=0.04), and there was a trend towards lower CD8+Tcm infiltration in TP53 mutant MSS group than that in TP53 wild-type MSS group (n=11, p=0.06). Conclusion: The infiltration level of CD8+ T cell in TP53 pathway wild-type MSS CRC patients was significantly higher than that in TP53 pathway mutant MSS CRC, and was comparable to that in MSI-H CRC, which implies the potential benefit of these patients from immune checkpoint inhibitor therapy. Citation Format: Yi Cai, Feilong Zhao, Xiaochen Zhao, Yuezong Bai. The enrichment of CD8+ T cell in TP53 pathway wild-type microsatellite stable colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1190.

ASO Author Reflections: ATMIN Altering the WNT Signaling Pathway via PARP1 in MSI-High Colorectal Cancer.

ASO Author Reflections: ATMIN Altering the WNT Signaling Pathway via PARP1 in MSI-High Colorectal Cancer.

Clinicopathological features of sporadic MSI colorectal cancer and Lynch syndrome: a single-center retrospective cohort study.

The clinical and pathological features of sporadic microsatellite instability-high (MSI) colorectal cancer (CRC) are still unclear. The present study aimed to clarify the clinicopathological features of sporadic MSI CRC in comparison with those of Lynch syndrome (LS) exploratorily. The present study was a single-center, retrospective cohort study. Sporadic MSI CRC was defined as MSI CRC with aberrant promoter hypermethylation of the MLH1 gene, while hereditary MSI CRC was defined colorectal cancer in patients with LS. In total, 2653 patients were enrolled; of these, 120 (4.5%) had MSI CRC, 98 had sporadic MSI CRC, and 22 had LS. Patients with sporadic MSI CRC were significantly older (p < 0.001) than those with LS and had a right-sided colonic tumor (p < 0.001) which was pathologically poorly differentiated or mucinous (p = 0.025). The overall survival rate was significantly lower in patients with stage I, II or III MSI CRC than in those with LS (p = 0.024). However, the recurrence-free survival rate did not differ significantly (p = 0.85). We concluded that patients with sporadic MSI are significantly older, tumors more likely to locate in the right-sided colon, pathologically poorly differentiated or mucinous, and worse overall survival than in those with LS.

ATMIN Suppresses Metastasis by Altering the WNT-Signaling Pathway via PARP1 in MSI-High Colorectal Cancer.

Constant DNA damage occurs in cells, and the cells are programmed to respond constitutively. This study explored the roles of ataxia-telangiectasia mutated interactor (ATMIN), one of the impaired pathways involving the DNA damage response (DDR) in mismatch repair-deficient [microsatellite instability (MSI)-high] colorectal carcinoma (CRC). Expression of ATMIN messenger RNA (mRNA) was detected in CRC specimens with microsatellite instability (MSI) characteristics. The effects of ectopic ATMIN expression and ATMIN knockdown on invasion abilities were evaluated in MSI-high cell lines, and liver metastasis ability was investigated in vivo. Protein-protein interactions were assessed by coimmunoprecipitation analyses in vitro. Decreased ATMIN expression was positively correlated with advanced stage of disease (P < 0.05), lymph node metastases (P < 0.05), and deeper invasion (P < 0.05) in MSI-high tumors. Transient or stable ATMIN knockdown significantly increased cell motility. Moreover, in the high-throughput microarray and gene set enrichment analysis, ATMIN was shown to act on the Wnt-signaling pathway via PARP1. This cascade influences β-catenin/transcription factor 4 (TCF4) binding affinity in MSI-high tumors, and PARP1 inhibition significantly decreased the number of metastases from ATMIN knockdown cancer cells. The results not only indicated the critical role of ATMIN, but also shed new light on PARP1 inhibitors, providing a basis for further clinical trials of MSI-high CRC.

PCN35 Systematic and Structured Reviews of the Disease Burden in Patients with Microsatellite Instability High (MSI-H) or Mismatch Repair Deficient (DMMR) Colorectal Cancer (CRC)

Literature reviews were undertaken to assess global disease burden of MSI-H/dMMR CRC Medline®, Embase®, Cochrane, EconLit, CRD York databases and select conferences were searched for studies reporting burden of MSI-H/dMMR CRC globally. Evidence was searched during 2009-19 (economic burden) and 2014-19 (epidemiology, treatment patterns and humanistic burden). Of 41,296 records screened - epidemiology (N=41), economic (N=2) humanistic burden (N=2) and treatment patterns (N=4) studies were reported for MSI-H/dMMR CRC. Included evidence showed prevalence of MSI-H/dMMR CRC ranged from 5.8% to 22% across disease stages with rates higher in earlier stages, >50 years of age, females, and Caucasians. Three country-specific real world studies reported common use of 5-FU- based treatments with either irinotecan, or oxaliplatin and with or without an EGFR or VEGF inhibitor for 1L MSI-H CRC. In response to a 2018 survey of global healthcare practitioners on their intended treatment plan for various case scenarios, 43%(1st line), 62%(2nd line) and 54%(3rd line) indicated preference for use of an immune checkpoint inhibitor. In a single institution, non-randomized study of 5-FU-treated patients, overall symptom burden (OR 2.48; 95% CI, 1.29-4.74) pain (3.06 [1.61-5.84]), fatigue (2.78 [1.41-5.49]), sleep (2.52 [1.32-4.08]); and drowsiness (2.51 [1.32-4.78]) was greater among those with MSI-H versus microsatellite stable tumors. Published evidence on the disease burden of MSI-H/dMMR CRC is sparse. Given the recent approvals and increased clinical development of immune checkpoint inhibitors in this high unmet need area, real-world and economic studies could further help to assess the disease burden.

Clinicopathologic variables and outcomes in elderly colorectal cancer patients with microsatellite instability and multiple primary malignancies.

e15516 Background: The biology of microsatellite instability-high (MSI-H) in elderly colorectal cancer (CRC) patients is attributed to hypermethylation of promoter region of genes coding for mismatch repair proteins. It is unknown if such patients are predisposed to other malignancies. It is also unknown if the presence or absence of multiple primary malignancies affects elderly MSI-H CRC patients' survival. We aimed to evaluate the clinicopathologic features and outcomes in elderly CRC patients with MSI-H and multiple primary malignancies. Methods: We analyzed the National Cancer Database and included elderly (≥ 65 years) patients with CRC diagnosed between 2010-2016. MSI status was determined using genetic and immunohistochemical testing and categorized as microsatellite stable (MSS) and MSI-H. We further categorized the population into single primary malignancy versus multiple primary malignancies. We compared the baseline characteristics using the Chi-square test. Kaplan-Meier and log-rank tests were performed to calculate the overall survival (OS). Results: Among 52,494 elderly CRC patients, 78.0% were MSS, and 22.0% were MSI-H. The probability of MSI-H disease increased with increasing age, female gender, and non-Hispanic White ethnicity (all p &lt; .001). MSI-H patients were associated with elevated CEA, wild-type KRAS, multiple neoplasms, right-sided tumors, stage II disease, and grade III/IV histology. The proportion of patients with multiple primary malignancies was higher in the MSI-H population versus MSS (36% vs. 31%, p &lt; 0.001). The rate of multiple primary malignancies increased with age in both groups. Among MSI-H CRC patients, the factors associated with multiple primary malignancies included female gender (61.6%), non-Hispanic White ethnicity (86.3%), comorbidity index ≥ 2 (14.8%), and right-sided tumors (77.2%). Multiple primary malignancies were more frequently associated with stage I-III CRC as compared to metastatic CRC. For stage III-IV elderly MSI-H patients, the utilization of chemotherapy was 57.8% overall, but it was not significantly different between single primary malignancy versus multiple primary malignancies groups. MSI-H patients with single primary malignancy had the highest OS, followed by MSS patients with single primary malignancy, MSI-H patients with multiple primary malignancies, and MSS patients with multiple primary malignancies (74.7, 66.7, 58.1, 54.8 mos, respectively) (log-rank p &lt; 0.001). Conclusions: Elderly CRC patients with MSI-H had a higher rate of multiple primary malignancies than MSS. This was associated with female gender, non-Hispanic White ethnicity, and right-sided tumor. MSI-H patients with single primary malignancy had the highest survival while the presence of multiple primary malignancies adversely affected survival in both MSI-H and MSS populations.

ENVASARC: A pivotal trial of envafolimab, and envafolimab in combination with ipilimumab, in patients with advanced or metastatic undifferentiated pleomorphic sarcoma or myxofibrosarcoma who have progressed on prior chemotherapy.

TPS11581 Background: Metastatic undifferentiated Pleomorphic Sarcoma (UPS) and the genetically related myxofibrosarcoma (MFS) are soft tissue sarcoma (STS) subtypes with poor prognoses. While responses to front line chemotherapy can approach 20%, efficacy remains limited in the 2nd line setting and beyond. Pazopanib, the only approved treatment in the refractory setting, has demonstrated an objective response rate (ORR) of 4%. Envafolimab is a single domain PD-L1 antibody administered rapidly by subcutaneous (SQ) injection that is being studied in two additional pivotal trials: microsatellite instability-high (MSI-H) cancer and biliary tract cancer. The activity of envafolimab appears to be similar to other PD-1 antibodies administered i.v. Envafolimab demonstrated a 32% objective response rate (ORR) in MSI-H colorectal cancer patients who failed three approved chemotherapeutics, similar to the ORR of 28% and 33% with nivolumab and pembrolizumab in these patient populations, respectively. The rationale for the ENVASARC trial is based on the previously reported activity of checkpoint inhibition in UPS/MFS. Single agent pembrolizumab demonstrated a 23% ORR, while the combination of nivolumab and ipilimumab demonstrated a 29% ORR in refractory UPS/MFS. Methods: ENVASARC (NCT 04480502) is a pivotal multicenter (at ̃25 U.S. centers) open-label, randomized, non-comparative, parallel cohort study of treatment with envafolimab 300 mg every 3 weeks by SQ injection (cohort A; n = 80) or envafolimab 300 mg every 3 weeks by SQ injection combined with ipilimumab 1 mg/kg every 3 weeks i.v. for four doses (cohort B; n = 80) in patients with locally advanced, unresectable or metastatic UPS/MFS who have progressed on one or two lines of prior therapy. The primary objective of each of parallel cohort is to demonstrate an ORR with a lower limit of the 95% confidence interval that excludes 5.0% in each cohort. If ≥ 9 responders are observed of the 80 patients enrolled in each cohort, then the lower bound of the 95% confidence interval will exclude 5.0%. Secondary endpoints include duration of response (DOR), PFS and OS. Key inclusion criteria: ≤ 2 prior lines of therapy (neoadjuvant and adjuvant therapy excluded), ECOG ≤ 1. Clinical trial information: NCT 04480502.

Microsatellite Instability in Colorectal Cancer Liquid Biopsy-Current Updates on Its Potential in Non-Invasive Detection, Prognosis and as a Predictive Marker.

Colorectal cancer (CRC) is the third most commonly-diagnosed cancer in the world and ranked second for cancer-related mortality in humans. Microsatellite instability (MSI) is an indicator for Lynch syndrome (LS), an inherited cancer predisposition, and a prognostic marker which predicts the response to immunotherapy. A recent trend in immunotherapy has transformed cancer treatment to provide medical alternatives that have not existed before. It is believed that MSI-high (MSI-H) CRC patients would benefit from immunotherapy due to their increased immune infiltration and higher neo-antigenic loads. MSI testing such as immunohistochemistry (IHC) and PCR MSI assay has historically been a tissue-based procedure that involves the testing of adequate tissue with a high concentration of cancer cells, in addition to the requirement for paired normal tissues. The invasive nature and specific prerequisite of such tests might hinder its application when surgery is not an option or when the tissues are insufficient. The application of next-generation sequencing, which is highly sensitive, in combination with liquid biopsy, therefore, presents an interesting possibility worth exploring. This review aimed to discuss the current body of evidence supporting the potential of liquid biopsy as a tool for MSI testing in CRC.

Expression of Thomsen-Friedenreich Antigen in Colorectal Cancer and Association with Microsatellite Instability.

Microsatellite instability (MSI) is a molecular phenotype due to a deficient DNA mismatch repair (dMMR). In colorectal cancer (CRC), dMMR/MSI is associated with several clinical and histopathological features, influences prognosis, and is a predictive factor of response to therapy. In daily practice, dMMR/MSI profiles are identified by immunohistochemistry and/or multiplex PCR. The Thomsen–Friedenreich (TF) antigen was previously found to be a potential single marker to identify MSI-high gastric cancers. Therefore, in this study, we aimed to disclose a possible association between TF expression and MSI status in CRC. Furthermore, we evaluated the relationship between TF expression and other clinicopathological features, including patient survival. We evaluated the expression of the TF antigen in a cohort of 25 MSI-high and 71 microsatellite stable (MSS) CRCs. No association was observed between the expression of the TF antigen and MSI-high status in CRC. The survival analysis revealed that patients with MSI-high CRC showed improved survival when the TF antigen was expressed. This finding holds promise as it indicates the potential use of the TF antigen as a biomarker of better prognosis in MSI-high CRCs that should be validated in an independent and larger CRC cohort.

Overall survival based on MSI and BRAF mutation status for stage II/III colorectal cancer.

132 Background: Colorectal cancer (CRC) is the second leading cause of cancer-associated deaths in the United States. Some of the poor prognostic factors for metastatic CRC (mCRC) include BRAF V600E mutation and microsatellite instability (MSI) that result from mutation or loss of mismatch-repair genes. While the prognostic value of MSI-high CRC for early-stage patients treated with resection and adjuvant chemotherapy is favorable, the prognostic value of BRAF mutation is still unclear. Furthermore, the impact of BRAF mutation with concurrent microsatellite instability on overall survival has not been well investigated. Methods: Here, we collected BRAF mutation status and MSI status of stage II/III CRC patients (n=106) treated at the University of Kansas Cancer Center between September 2009 and July 2020 and compared overall survival between 4 subtypes:MSI-H/BRAF mutant (n=16), MSS/BRAF mutant (n=4), MSI-H/BRAF WT (n=17) and MSS/BRAF WT (n=69), further stratifying patients by age at diagnosis and tumor location. Molecular data were obtained from molecular oncology laboratory as PCR or IHC-based or acquired from outside records. Subgroup analyses were done for stage II and stage III cancers. Results: Table shows the patient characteristics. From our preliminary analysis, MSI-H CRC was found to be primarily a right-sided tumor (MSI-H/BRAF mutant: 94% and MSI-H/BRAF WT 76%). On the contrary, MSS CRC had a more heterogenous localization, spanning left colon, right colon and rectum. In our patient cohort, median survival was not reached for stage II patients whereas for stage III patients, BRAF mutation was associated with poor median survival irrespective of MSI status (MSS/BRAF mutant: 27 months and MSI-H/BRAF mutant 29 months). Median overall survival was found to be 87 months, not reached, 27 months and 29 months for MSS/BRAF WT, MSI-H/BRAF WT, MSS/BRAF mutant and MSI-H/BRAF mutant, respectively. Although associated with poor survival, MSI-H/BRAF mutant displayed later age at diagnosis (mean age 73) compared to MSS/BRAF mutant (mean age 60, p-value&lt;0.029). Conclusions: Our finding suggests that BRAF mutation has poor prognosis even at earlier stages of the disease and that MSS/BRAF mutation, in particular, has the worst prognostic features. These findings highlight the need for BRAF-targeted therapy for CRC at any stage. Due to small sample size, however, our results warrant validation in a larger cohort. [Table: see text]