High Microsatellite Instability Research Articles

620P Efficacy, safety and PKPD of 23ME-00610, a first-in-class anti-CD200R1 antibody, in patients with tumor mutational burden-high (TMB-H) and/or microsatellite instability-high (MSI-H) cancers: Results from an expansion cohort

620P Efficacy, safety and PKPD of 23ME-00610, a first-in-class anti-CD200R1 antibody, in patients with tumor mutational burden-high (TMB-H) and/or microsatellite instability-high (MSI-H) cancers: Results from an expansion cohort

Integrative analysis of the immunological significances of guanylate binding protein family genes in microsatellite stability colorectal cancer

BackgroundMicrosatellite stability (MSS) colorectal cancer (CRC) has poor sensitivity to immunotherapy and its underlying mechanisms are still unclear. Guanylate binding proteins (GBPs) are a family of GTPase involving innate immune responses by providing defense against invading microbes and pathogens. However, the immunological significances of GBPs in MSS CRC remain unknown. MethodsWe utilized bioinformatic tools to comprehensively analysis the expression pattern, clinical relevance, prognostic value, biological function, and immunoregulation effect of distinct GBP members in MSS CRC. ResultsThe expression of all seven GBPs in MSS samples are remarkably decreased compared to microsatellite instability-high (MSI-H) samples. Among them, GBP1/2/4/5 are obviously correlated with distant metastasis status. High expression of GBP1/4/5/6 was remarkably related to favorable overall survival (OS) and progression-free survival (PFS) in CRC patients with MSS tumor. Subsequent enrichment analysis revealed that Interferon-gamma (IFN-γ) and NOD-like receptor signaling are the most relevant functions. Besides, the expression patterns of GBPs are remarkably associated with several tumor infiltrated immune cells (e.g. regulatory T cells, CD4+ T cells, and macrophages) and diverse immunoregulatory molecules (e.g. immune checkpoint biomarkers (ICBs) and major histocompatibility complex (MHC) molecules). Moreover, high GBP1/2/4/5 expression predicted better immunotherapy responsiveness in immunotherapy cohorts. ConclusionThese findings might provide novel insights for the identification of therapeutic targets and potential prognostic biomarkers of GBP family in CRC with MSS samples.

New systemic treatment options for advanced cholangiocarcinoma.

Cholangiocarcinoma (CCA) is a rare and aggressive cancer, mostly diagnosed at advanced or metastatic stage, at which point systemic treatment represents the only therapeutic option. Chemotherapy has been the backbone of advanced CCA treatment. More recently, immunotherapy has changed the therapeutic landscape, as immune checkpoint inhibitors have yielded the first improvement in survival and currently, the addition of either durvalumab or pembrolizumab to standard of care cisplatin plus gemcitabine represents the new first-line treatment option. However, the use of immunotherapy in subsequent lines has not demonstrated its efficacy and therefore, it is not approved, except for pembrolizumab in the selected microsatellite instability-high population. In addition, advances in comprehensive genomic profiling have led to the identification of targetable genetic alterations, such as isocitrate dehydrogenase 1 (IDH1), fibroblast growth factor receptor 2 (FGFR2), human epidermal growth factor receptor 2 (HER2), proto-oncogene B-Raf (BRAF), neurotrophic tropomyosin receptor kinase (NTRK), rearranged during transfection (RET), Kirsten rat sarcoma virus (KRAS), and mouse double minute 2 homolog (MDM2), thus favoring the development of a precision medicine approach in previously treated patients. Despite these advances, the use of molecularly driven agents is limited to a subgroup of patients. This review aims to provide an overview of the newly approved systemic therapies, the ongoing studies, and future research challenges in advanced CCA management.

227TiP A phase II, open label, randomized, non-comparative cohorts study of adjuvant atezolizumab or atezolizumab plus tiragolumab in solid tumors with resectable disease with intermediate-high risk of recurrence and high tumor mutational burden (TMB-H) or microsatellite instability (MSI-H)

227TiP A phase II, open label, randomized, non-comparative cohorts study of adjuvant atezolizumab or atezolizumab plus tiragolumab in solid tumors with resectable disease with intermediate-high risk of recurrence and high tumor mutational burden (TMB-H) or microsatellite instability (MSI-H)

Comprehensive Analysis of Microsatellite Instability in Canine Cancers: Implications for Comparative Oncology and Personalized Veterinary Medicine.

Microsatellite instability (MSI) is a crucial feature in cancer biology, yet its prevalence and significance in canine cancers remain largely unexplored. This study conducted a comprehensive analysis of MSI across 10 distinct canine cancer histotypes using whole-exome sequencing data from 692 tumor-normal sample pairs. MSI was detected in 64% of tumors, with prevalence varying significantly among cancer types. B-cell lymphomas exhibited the highest MSI burden, contrasting with human studies. A novel "MSI-burden" score was developed, correlating significantly with tumor mutational burden. MSI-high (MSI-H) tumors showed elevated somatic mutation counts compared to MSI-low and microsatellite stable tumors. The study identified 3632 recurrent MSI-affected genomic regions across cancer types. Notably, seven of the ten cancer types exhibited MSI-H tumors, with prevalence ranging from 1.5% in melanomas to 37% in B-cell lymphomas. These findings highlight the potential importance of MSI in canine cancer biology and suggest opportunities for targeted therapies, particularly immunotherapies. The high prevalence of MSI in canine cancers, especially in B-cell lymphomas, warrants further investigation into its mechanistic role and potential as a biomarker for prognosis and treatment response.

Clinical significance of lympho-vascular space invasion in different molecular subtypes of endometrial carcinoma

Objective: To analyze the lympho-vascular space invasion (LVSI) in different molecular subtypes of the cancer genome atlas (TCGA) molecular subtypes of endometrial cancer (EC) and to evaluate the prognostic value of LVSI in EC patients with different molecular subtypes. Methods: A total of 258 patients diagnosed EC undergoing surgery in Peking University People's Hospital from January 2016 to June 2022 were analyzed retrospectively. Among 258 patients, 14 cases were classified as POLE-ultramutated subtype, 43 as high-microsatellite instability (MSI-H) subtype, 155 as copy-number low (CNL) subtype, and 46 as copy-number high (CNH) subtype. Fifty-four patients were positive for LVSI, while 203 tested negative. Results: (1) The incidence of LVSI was found to be highest in the CNH subtype (32.6%,15/46), followed by the MSI-H subtype (27.9%, 12/43), the CNL subtype (16.9%, 26/154), and the POLE-ultramutated subtype (1/14), with statistically significant differences (χ2=7.79, P=0.044). (2) Staging and deep myometrial invasion were higher in the LVSI positive group than those in the LVSI negative group (all P<0.05), except for the POLE-ultramutated subtype. The grade, lymph node metastasis, and the expression of nuclear antigen associated with cell proliferation (Ki-67) were significantly higher in LVSI positive patients than those in LVSI negative EC patients with both MSI-H and CNL subtypes (all P<0.05). In CNL subtypes patients, LVSI was also associated with age, histology subtype,and progesterone receptor (PR; all P<0.05). (3) Of the 257 EC patients, 25 cases recurred during the follow-up period, with a recurrence rate of 9.7% (25/257); among them, the recurrence rate of LVSI positive patients was 22.2% (12/54), which was significantly higher than those with LVSI negative (6.4%, 13/203; χ2=12.15, P<0.001). During the follow-up period, none of the 14 patients with POLE-ultramutated had recurrence; among CNL patients, the recurrence rate was 19.2% (5/26) in LVSI positive patients, which was significantly higher than that in LVSI negative ones (5.5%, 7/128; χ2=3.94, P=0.047); where as no difference were found in both MSI-H [recurrence rates in LVSI positive and negative patients were 2/12 and 9.7% (3/31), respectively] and CNH subtype [recurrence rates between LVSI positive and negative patients were 5/15 and 9.7% (3/31), respectively] EC patients (both P>0.05). After log-rank test, the 3-year recurrence free survival (RFS) rate were significantly lower in LVSI positive patients from CNL subtype and CNH subtype than those in LVSI negative patients (CNL: 80.8% vs 94.5%; CNH: 66.7% vs 90.3%; both P<0.05). (4) Lymph node metastasis (HR=6.93, 95%CI: 1.15-41.65; P=0.034) had a significant effect on the 3-year RFS rate of EC patients with MSI-H subtype. Multivariate analysis revealed that PR expression (HR=0.04, 95%CI: 0.01-0.14;P<0.001) was significantly associated with the 3-year RFS rate of CNL subtype patients. Conclusions: LVSI has the highest positivity rate in CNH subtype, followed by MSI-H subtype, CNL subtype, and the lowest positivity rate in POLE-ultramutated subtype. LVSI is significantly associated with poor prognosis in CNL subtype patients and may affect the prognosis of CNH subtype patients. However, LVSI is not an independent risk factor for recurrence across all four TCGA molecular subtypes.

The use of immune checkpoint inhibitors in advanced gastric/gastroesophageal adenocarcinomas - real-world evidence and the use of alternative dosing.

Immune check point inhibitors (ICIs) have an established role in Microsatellite-Instability-High (MSI-H) and Combined Positive Score (CPS) high advanced gastric/gastroesophageal (G/GE) adenocarcinomas, but there is limited real world data with regard to practice patterns, and efficacy of standard doses (SD-ICIs) and alternative lower doses (LD-ICIs). A retrospective study of patients with advanced G/GE adenocarcinomas receiving ICIs was conducted. The primary endpoint of the study was 12-month overall survival (OS), which was computed by Kaplan-Meier method. A total of 91 patients were available for analysis during the study period. Seventy-four patients (81%) received nivolumab, while the remaining received pembrolizumab. Fifteen patients (16%) had MSI-H status and had a 12-month OS of 60% and median OS of 15 months (median follow-up - 38.3 months). In the Microsatellite-Stable (MSS) cohort (84%; n = 76), ICIs (combined with chemotherapy) were used predominantly in pre-treated patients (54%; n = 41). Patients with CPS ≥5 (72%; n = 55) had improved survival compared to patients with CPS <5 (28%; n = 21) (12-month OS: 52% vs. 26%; Median OS: 12.8 months vs. 3.2 months; p = 0.005). There was no difference in survival between patients who received SD-ICIs (54%; n = 41) and LD-ICIs (46%; n = 35) (12-month OS: 42% vs. 48%; Median OS: 8.7 months vs. 11 months; p = 0.44). Patients with advanced G/GEJ adenocarcinomas in the real world predominantly received ICIs during later lines of therapy as opposed to first line therapy. Using a CPS cutoff of ≥5 as opposed to CPS <5 predicts for improved survivals in MSS patients and patients receiving low dose ICIs have similar survival outcomes to patients receiving standard dose ICIs within the confines of a heterogenous study cohort.

Immune checkpoint inhibitors for patients with mismatch-repair deficient or microsatellite instability-high advanced cancers: a meta-analysis of phase I-III clinical trials.

Mismatch-repair deficient (dMMR) and microsatellite instability-high (MSI-H) cancers are associated with an increased number of somatic mutations, which can render tumors more susceptible to immune checkpoint blockade. However, a comprehensive evaluation of the efficacy profile of immune checkpoint inhibitors in this patient population across multiple cancer types is lacking. This study aims to address this knowledge gap by synthesizing data from Phase I-III clinical trials. A systematic search was conducted in PubMed, Embase, the Cochrane Central Register of Controlled Trials and Google Scholar from inception until June, 2024. Eligible studies included randomized controlled trials (RCTs), non-randomized comparative studies, and single-arm trials investigating immune checkpoint inhibitors in patients with dMMR/MSI-H advanced cancers. The primary outcome was objective response rate (ORR), and the secondary outcomes included disease control rate (DCR), 1-year, 2-year, and 3-year overall survival (OS) and progression-free survival (PFS) rates. Subgroup analyses were conducted for the primary outcome stratified by major study characteristics. Of the 10802 identified studies, 19 trials in 25 studies totaling 2052 participants met the inclusion criteria and were included in the meta-analysis. The pooled ORR was 41.7% (95% CI, 35.7%-47.7%). The pooled DCR was 68.9% (95% CI, 62.2%-75.7%). The pooled 12-month, 24-month and 36-month OS rates were 29.1% (95% CI, 19.9%-38.3%), 35.8% (95% CI, 23.6%-48.0%), and 35.8% (95% CI, 23.6%-48.0%), respectively. The pooled 12-month, 24-month and 36-month PFS rates were 46.4% (95% CI, 39.1%-53.8%), 67.0% (95% CI, 55.2%-78.8%), and 63.1% (95% CI, 37.3%-88.9%), respectively. The study establishes the therapeutic potential of immune checkpoint inhibitors in dMMR/MSI-H advanced cancers, highlighting the importance of MSI status in this context. Further head-to-head comparisons are needed to conclusively determine MSI's predictive power relative to proficient mismatch-repair/ microsatellite stable (pMMR/MSS) tumors.

Reinvigoration of cytotoxic T lymphocytes in microsatellite instability-high colon adenocarcinoma through lysosomal degradation of PD-L1

Compensation and intracellular storage of PD-L1 may compromise the efficacy of antibody drugs targeting the conformational blockade of PD1/PD-L1 on the cell surface. Alternative therapies aiming to reduce the overall cellular abundance of PD-L1 thus might overcome resistance to conventional immune checkpoint blockade. Here we show by bioinformatics analysis that colon adenocarcinoma (COAD) with high microsatellite instability (MSI-H) presents the most promising potential for this therapeutic intervention, and that overall PD-L1 abundance could be controlled via HSC70-mediated lysosomal degradation. Proteomic and metabolomic analyses of mice COAD with MSI-H in situ unveil a prominent acidic tumor microenvironment. To harness these properties, an artificial protein, IgP β, is engineered using pH-responsive peptidic foldamers. This features customized peptide patterns and designed molecular function to facilitate interaction between neoplastic PD-L1 and HSC70. IgP β effectively reduces neoplastic PD-L1 levels via HSC70-mediated lysosomal degradation, thereby persistently revitalizing the action of tumor-infiltrating CD8 + T cells. Notably, the anti-tumor effect of lysosomal-degradation-based therapy surpasses that of antibody-based immune checkpoint blockade for MSI-H COAD in multiple mouse models. The presented strategy expands the use of peptidic foldamers in discovering artificial protein drugs for targeted cancer immunotherapy.

Mismatch repair deficiency in bilateral breast cancer

BackgroundSince the FDA approved immune-enhancing therapies for patients with high microsatellite instability (MSI-H) and/or mismatch repair deficiency (dMMR), recognizing these biomarkers in solid tumors has gained clinical importance. Although MSI-H and dMMR are considered uncommon in breast cancer, previous studies on bilateral breast cancer (biBC) identified a surprisingly high frequency of MSI.MethodsIn this study, we aimed to describe the prevalence of dMMR and its association with clinicopathologic parameters in biBC. We performed immunohistochemistry with anti-MMR proteins on tissue microarrays (TMAs) with 58 bilateral breast cancer cases. The biomarkers used were MLH1, PMS2, MSH2, MSH6, ER, PR, HER2 and Ki67. SPSS was used for data analysis.ResultsFour (6.9%) cases showed dMMR on TMAs. Three (75%) of the dMMR cases were luminal and one (25%) was triple negative. Two biBC cases presented unilateral dMMR. No association between dMMR status and clinicopathologic parameters was found.ConclusionsThis work highlights a noticeable frequency of dMMR in bilateral breast cancer and builds upon previous research in this area, suggesting routine MMR protein testing as part of the immunohistochemical panel for biBC to identify candidates for immune-enhancing therapies.

Gender medicine in diseases of the upper gastrointestinal tract

Benign and malignant diseases of the upper gastrointestinal tract show gender-specific differences. The frequent gastroesophageal reflux disease is aprime example: men have an erosive reflux disease more often than women and are also younger at the time of onset. The rate of progression to a metaplastic Barrett's esophagus is also higher in men. In the case of achalasia, there are indications that surgical treatment by laparoscopic Heller's myotomy and semifundoplication 180° according to Dor leads to amarkedly better improvement in the symptoms in women compared to men, although they showed amore pronounced dilation of the tubular esophagus. The female hormone status influences the localization and histopathology of adenocarcinoma of the esophagogastric junction and gastric carcinoma. Premenopausal and postmenopausal carcinomas differ significantly in women. In addition, high microsatellite instability (MSI high) is more frequent in women and is associated with agenerally significantly better prognosis. The MSI high gastric carcinomas of women show better survival than MSI high carcinomas of men. The future inclusion of gender-specific aspects in studies of the upper gastrointestinal tract is desirable in order to generate adequate data and to enable differentiated treatment stratification in the future.

Pathological complete response achieved with FLOT chemotherapy in two patients with MSI-H esophagogastric junction and gastric adenocarcinoma.

Globally, more than 1 million new cases of gastric cancer were estimated in 2020, ranking fourth in cancer mortality. Currently although in resectable gastric cancer and esophagogastric junction (EGJ) adenocarcinoma a perioperative triplet chemotherapy regimen including a fluoropyrimidine, a platinum compound and docetaxel (FLOT) demonstrated a better overall survival, the survival rate is still very low, and a massive effort is still required to improve clinical prognosis. High microsatellite instability (MSI-H) status in gastric cancer is a favorable prognostic factor but poor data are available on its predictive role for perioperative FLOT chemotherapy in resectable gastric cancer. Here, we presented the case of two patients with advanced MSI-H gastric cancer/EGJ adenocarcinoma who had no residual tumor following neoadjuvant FLOT chemotherapy maintaining a complete response for more than 30 months, suggesting MSI-H status to be a positive prognostic marker also in patients treated with a taxane-containing triplet in this setting. We also discuss the future perspectives including the opportunity to achieve excellent clinical outcomes with immune checkpoint inhibitor (ICI)-based regimens.

Occult gastric carcinoma with microsatellite instability diagnosed 10 years after excision of metastatic lymph node: a case report

BackgroundSuprapancreatic lymph node metastasis is one of the usual routes for gastric cancer. However, it is rare for the primary lesion to be found several years after resection of the suprapancreatic metastatic lymph node. This is a report of occult gastric carcinoma with microsatellite instability diagnosed 10 years after excision of a metastatic lymph node.Case presentationA 55-year-old female presented with suprapancreatic lymph node swelling during a medical examination. Gastroscopy revealed no malignancy. We performed an excisional biopsy via laparotomy and histologically suspected metastatic cancer of unknown origin. After nine and a half years, we detected early gastric cancer by gastroscopy and performed a distal gastrectomy. The gastric tumor was pathologically similar to the previous suprapancreatic tumor. Immunohistochemical examination revealed that both the stomach and suprapancreatic lymph node exhibited microsatellite instability, suggesting that the two lesions were of the same origin.ConclusionsThis case is considered valuable because there have been no previous reports of gastric cancer with characteristics of high microsatellite instability in which the primary tumor was identified a long time after resection of metastatic lesions.

Ancestry-, Sex-, and Age-Based Differences of Gene Alterations in NSCLC: From the Real-World Data of Cancer Genomic Profiling Tests.

Some genomic alterations in non-small cell lung cancer (NSCLC) are known to differ according to race, sex, or age. These studies have been limited in sample size and thus they cannot detect the differences precisely and comprehensively. Tissue-based comprehensive genomic profiling was performed on 75,362 patients with NSCLC from the United States during routine clinical care. Additionally, we examined data of a Japanese NSCLC cohort with 1,019 patients. In the US cohort, 296 genes were examined for pathogenic alterations. Predominant genetic ancestry was inferred using a SNP-based approach, and patients were categorized into European (EUR), African (AFR), East Asian (EAS), Admixed American (AMR), and South Asian (SAS) ancestry groups. Patients were additionally stratified by histologic type, age (<40/≥40 years, <75/≥75 years), and sex. The prevalence of high tumor mutational burden (TMB-High) and microsatellite instability status was also calculated. Stratified by ancestry, EGFR alterations were significantly enriched in EAS versus other ancestry groups. The prevalence of ALK was significantly higher in the AMR, EAS, and SAS patients than in AFR and EUR patients. KRAS and STK11 were enriched in EUR and AFR patients versus other groups. TMB-High was significantly enriched in AFR patients versus all other groups. An analysis based on sex revealed differences in prevalence of alterations in 80 genes and TMB-High status. For example, EGFR, ALK, BRAF, and KRAS alterations were significantly enriched in females, whereas TP53, STK11, KEAP1, and TMB-High were significantly enriched in males. With respect to age, the prevalence of alterations in 41 genes, including ALK, RET, MET, EGFR, STK11, KEAP1, BRAF, and KRAS, as well as TMB-High, were significantly different between patients aged <40 years and those aged ≥40 years. Comprehensive analysis from a large real-world dataset revealed ancestry-associated differences in genomic alterations in NSCLC. Age- and sex-related differences in prevalence of genomic alterations and TMB-High status were also observed.

Management of HER2-positive and microsatellite instability-high advanced gastric cancer: a case report

Chemotherapy for advanced gastric cancer has progressed significantly in the past few decades. Biomarker-specific drugs, including anti-human epidermal growth factor receptor 2 (HER2) drugs for HER2-positive patients and immune checkpoint inhibitors for those with microsatellite instability-high (MSI-H), have become common. However, patients who are positive for HER2 and have MSI-H are extremely rare, and there are no established treatments for these patients. We present the case of a 75-year-old, male patient with gastric cancer with lymph node metastases and liver infiltration. Biomarker analysis revealed HER2 3 + , loss of MLH1, and MSI-H. After three cycles of S-1, oxaliplatin, and trastuzumab, the primary tumor and metastases shrank markedly. He subsequently underwent gastrectomy and hepatectomy as conversion surgery, achieving a pathologically complete response. He has been recurrence-free for seven months postoperatively. The present case demonstrated the efficacy of trastuzumab-containing chemotherapy followed by conversion surgery in a patient with HER2-positive, MSI-H, advanced gastric cancer.

WRN Helicase: Is There More to MSI-H than Immunotherapy?

In this issue, Picco and colleagues provide further evidence that WRN inhibitors are synthetically lethal in microsatellite instability-high (MSI-H) cancers and function by blocking the helicase domain of select WRN residues. They demonstrate that WRN inhibitors may be even more effective in a subset of MSI-high tumors with (TA)n repeat expansions, which represents a possible strategy in clinical development. See related article by Picco et al., p. 1457 (1).

RPL22 is a tumor suppressor in MSI-high cancers and a splicing regulator of MDM4

Microsatellite instability-high (MSI-H) tumors are malignant tumors that, despite harboring a high mutational burden, often have intact TP53. One of the most frequent mutations in MSI-H tumors is a frameshift mutation in RPL22, a ribosomal protein. Here, we identified RPL22 as a modulator of MDM4 splicing through an alternative splicing switch in exon 6. RPL22 loss increases MDM4 exon 6 inclusion and cell proliferation and augments resistance to the MDM inhibitor Nutlin-3a. RPL22 represses the expression of its paralog, RPL22L1, by mediating the splicing of a cryptic exon corresponding to a truncated transcript. Therefore, damaging mutations in RPL22 drive oncogenic MDM4 induction and reveal a common splicing circuit in MSI-H tumors that may inform therapeutic targeting of the MDM4-p53 axis and oncogenic RPL22L1 induction.

RNF43 in cancer: Molecular understanding and clinical significance in immunotherapy.

Identifying biomarkers to predict immune checkpoint inhibitor (ICI) efficacy is warranted. Considering that somatic mutation-derived neoantigens induce strong immune responses, patients with a high tumor mutational burden reportedly tend to respond to ICIs. Therefore, the original function of neoantigenic mutations and their impact on the tumor microenvironment (TME) require attention. RNF43 is a type of RING E3 ubiquitin ligase, and long-term survivors in most cancers had conserved patterns of mutations of RNF43. Also, high microsatellite instability patients had a higher RNF43 mutation rate compared with microsatellite stability tumor patients, who were more sensitive to ICI treatment. Therefore, RNF43 has become a promising biomarker of immunotherapy in a wide range of cancers. This review focuses on the up-to-date knowledge of RNF43 mutation in cancer. We summarize the cancer hallmarks involving activities regulated by RNF43 and highlight its extremely sophisticated regulation of WNT signaling and tumor microenvironment. The key genes interacting with RNF43 have also been summarized and discussed. Additionally, we highlight and propose new strategies of targeting RNF43 and RNF43-based combinations with established immunotherapy and combination therapy. These efforts may provide new perspectives for RNF43-based target therapy in cancer.

Performance of Low-Dose Immunotherapy and Standard-Dose Immunotherapy in Microsatellite Instability-High Metastatic Colorectal Cancer: Real-World Data (CLouD-High Study).

Standard-dose immune checkpoint inhibitors (SD-ICIs) are the standard of care as initial therapy in microsatellite instable-high (MSI-H) advanced/metastatic colorectal adenocarcinomas (mCRC), but there are preclinical data to suggest that low-dose ICIs (LD-ICI) might also have similar efficacy. A retrospective study of patients with MSI-H mCRC receiving ICIs between June 2017 and January 2023 was conducted. The primary end point of the study was 12-month progression-free survival (PFS), which was computed using the Kaplan-Meier method. A total of 65 patients were available for analysis during the study period. Sixty patients (92%) received nivolumab, whereas the remaining received pembrolizumab. First-line ICIs were received by 18 patients (28%), whereas 47 patients (72%) received ICIs during later lines. Thirty patients (47%) received LD-ICIs (all received nivolumab), with the remaining receiving SD-ICIs (53%). At a median follow-up of 16.5 (95% CI, 11.8 to 21.2) months, median PFS was not reached in the entire cohort. The 12-month PFS rate in the LD-ICI cohort was 90%, whereas it was 75.8% in the SD-ICI cohort. There were no statistical differences in patients receiving ICIs as first-line therapy (12 months PFS-94.4%) or during later lines of therapy (12-month PFS-77.9%; P = .56). ICIs in the current study show survivals which are similar to those seen in seminal trials in patients with MSI-H mCRC. Low-dose ICIs appear to work in MSI-H mCRC and should be explored prospectively in clinical trials. Patients with MSI-H status should be exposed to ICIs, whether initially or later during treatment, whenever feasible.

Current laboratory testing practices for mismatch repair deficiency and microsatellite instability testing: A survey-based review of current laboratory practices.

To describe mismatch repair (MMR) and microsatellite instability (MSI) testing practices in laboratories using the College of American Pathologists (CAP) MSI/MMR proficiency testing programs prior to the 2022 publication of the MSI/MMR practice guidelines copublished by CAP and the Association of Molecular Pathology (AMP). Data from supplemental questionnaires provided with the 2020-B MSI/MMR programs to 542 laboratories across different practice settings were reviewed. Questionnaires contained 21 questions regarding the type of testing performed, specimen/tumor types used for testing, and clinical practices for checkpoint blockade therapy. Domestic laboratories test for MSI/MMR more often than international laboratories (P = .04) and academic hospitals/medical centers test more frequently than nonhospital sites/clinics (P = .03). The most commonly used testing modality is immunohistochemistry, followed by polymerase chain reaction, then next-generation sequencing. Most laboratories (72.6%; 347/478) reported awareness of the use of immune checkpoint inhibitor therapy for patients with high MSI or MMR-deficient results. The results demonstrate the state of MMR and MSI testing in laboratories prior to the publication of the CAP/AMP best practice guidelines, highlighting differences between various laboratory types. The findings indicate the importance of consensus guidelines and provide a baseline for comparison after their implementation.