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Purpose of Review: This review will explore various strategies to rendering MSS mCRCs susceptible to ICI. Moreover, we will provide an overview of potential biomarkers that may aid to better patient selection, and discuss ongoing efforts in this area of research. Recent Findings: Colorectal cancer (CRC) ranks among the top three most common cancers worldwide. While significant advances in treatment strategies have improved the prognosis for patients in the early stages of the disease, treatment options for metastatic CRC (mCRC) remain limited. Although immune checkpoint inhibitors (ICI) have revolutionized the treatment of several malignancies, its efficacy in mCRC is largely confined to patients exhibiting a high microsatellite instability status (MSI-H). However, the vast majority of mCRC patients do not exhibit a MSI-H, but are microsatellite stable (MSS). In these patients ICIs are largely ineffective. Summary: So far, ICIs do not play a crucial role in patients with MSS mCRC, despite the promising data for inducing long-term remissions in other tumour entities. For this reason, novel treatment strategies are needed to overcome the primary resistance upon ICI in patients with MSS. [ABSTRACT FROM AUTHOR]

Background: Programmed cell death receptor 1 (PD-1) and programmed cell death ligand 1 (PD-L1) are important immune checkpoint molecules that contribute to tumor immune evasion. However, the main treatment modalities for patients with early and intermediate stage colorectal cancer (CRC) are surgery, and the role of PD-1/PD-L1 inhibitors in these patients is not yet clear. Therefore, this study aims to review the treatment progress of PD-1/PD-L1 inhibitors for early- and intermediate-stage microsatellite high-instability (MSI-H) and stable (MSS) colorectal cancer, in order to provide more options for patients with early- and intermediate-stage colorectal cancer. Materials and methods: A scoping review of clinical trial registries (Clinicaltrials.gov and EU clinical trial registers) and PubMed/Medline database of trials on PD-1/PD-L1 Inhibitors for early and middle-stage MSI-H and MSS CRC was done up to March 2024. Results: A total of 19 trials related to early to mid-stage MSH-I or MSS CRC were included. Among them, 6 trials are in recruiting status, 3 trials are in active, not recruiting status, 3 trials are completed, 1 trial is terminated, and 1 trial is unknown. Of these, 9 trials involve MSI-H type CRC, and 10 trials involve MSS type CRC. Preclinical phase I/II trials are predominant, with only 3 clinical phase III trials. In trials related to MSI-H type CRC, 4 studies involve PD-1/PD-L1 inhibitors combined with neoadjuvant therapy, and 5 studies involve combination therapy. In trials related to MSS type CRC, 3 studies involve PD-1/PD-L1 inhibitors combined with targeted therapy, 2 studies involve PD-1/PD-L1 inhibitors combined with chemotherapy, 1 study involves PD-1/PD-L1 inhibitor combined immunotherapy, 1 study involves PD-1/PD-L1 inhibitors combined with bacterial therapy, and 3 studies involve PD-1/PD-L1 inhibitors combined with comprehensive therapy. As for primary outcome measures, 4 trials select pathological complete response rates, 3 trials select progression-free survival rate, 3 trials select objective response rate, 3 trials select overall survival rate, 4 trials select disease-free survival rate, 1 trial selects clinical complete response rate, and 1 trial selects percentage of participants with a dose-limiting toxicity. Conclusion: For early- and middle-stage MSI-H and MSS CRC, PD-1/PD-L1 inhibitors have shown some therapeutic efficacy, as evidenced by phase I/II studies. However, contemporary trial designs exhibit heterogeneity, with relatively few inclusion criteria, the use of various drug combinations and regimens, and significant variations in reported endpoints. Nevertheless, more double-arm, multicenter, randomized controlled trials are still needed to confirm the efficacy of immunotherapy. [ABSTRACT FROM AUTHOR]

Purpose: Clinical practice guidelines recommend that all patients with metastatic colorectal cancer (mCRC) should be tested for mismatch repair deficiency (dMMR) or microsatellite instability-high (MSI-H). We aimed to describe the dMMR/MSI-H testing practice in patients with mCRC in Spanish centers. Methods: Multicenter, observational retrospective study that included patients newly diagnosed with mCRC or who progressed to a metastatic stage from early/localized stages. Results: Three hundred patients were included in the study from May 2020 through May 2021, with a median age of 68 years, and two hundred twenty-five (75%) had stage IV disease at initial diagnosis; two hundred eighty-four patients received first-line treatment, and dMMR/MSI-H testing was performed in two hundred fifty-one (84%) patients. The results of the dMMR/MSI-H tests were available in 61 (24%) of 251 patients before the diagnosis of metastatic disease and in 191 (81%) of 236 evaluable patients for this outcome before the initiation of first-line treatment. Among the 244 patients who were tested for dMMR/MSI-H with IHC or PCR, 14 (6%) were MMR deficient. The most frequent type of first-line treatment was the combination of chemotherapy and biological agent, that was received by 71% and 50% of patients with MMR proficient and deficient tumors, respectively, followed by chemotherapy alone, received in over 20% of patients in each subgroup. Only 29% of dMMR/MSI-H tumors received first-line immunotherapy. Conclusion: Our study suggests that a high proportion of patients with mCRC are currently tested for dMMR/MSI-H in tertiary hospitals across Spain. However, there is still room for improvement until universal testing is achieved. Trial registration: Not applicable. [ABSTRACT FROM AUTHOR]

Opinion statement: Neoadjuvant chemotherapy is safe for patients with locally advanced colon cancer (LACC). The FOxTROT trial demonstrated a reduction in residual and recurrent cancer at 2 years with neoadjuvant chemotherapy for patients with cT3-4 LACC. Preoperative chemotherapy should be avoided, if possible, for patients with dMMR LACC, as over 50% of dMMR cancers have no pathologic response. Early universal testing of MMR status is critical to selecting the appropriate neoadjuvant therapy. Concerns about CT staging of LACC have limited uptake of neoadjuvant chemotherapy, as approximately 25% of patients with cT3-T4 cancer on CT have low-risk stage II disease. Development of CT criteria for malignant nodes should reduce the risk of over-staging. A multidisciplinary approach is needed to identify patients for neoadjuvant therapy. Neoadjuvant immunotherapy is safe and results in dramatic pathologic responses in patients with dMMR LACC. Longer follow-up is needed to determine if the exceptionally high pathologic response rates observed will translate into long-term remission. Remarkably, neoadjuvant immunotherapy has been found to cause major pathologic responses in a subset of patients with pMMR LACC, indicating the potential to cure more patients with this common cancer. Patients with cT4 LACC, whether stage II or III, have a substantial risk of recurrence despite adjuvant fluoropyrimidine plus oxaliplatin chemotherapy. We recommend neoadjuvant systemic therapy for all patients with cT4b LACC (dMMR and pMMR). Features of T4b disease are routinely reported by radiology. We use three cycles of FOLFOX chemotherapy for patients with cT4b pMMR LACC, due to the high rate of compliance and improvement in residual and recurrent disease. Patients with cT4b dMMR LACC should receive neoadjuvant immunotherapy, if there are no contraindications. Clinical trials of neoadjuvant therapy for LACC are of great interest and should provide training for radiologists to identify eligible patients. Results are anticipated from multiple ongoing trials of neoadjuvant chemotherapy, immunotherapy, and targeted therapy for pMMR LACC and immunotherapy for dMMR LACC. [ABSTRACT FROM AUTHOR]

About half of hereditary non-polyposis colorectal cancers (HNPCCs) fulfilling the Amsterdam criteria (AC) do not display evidence of mismatch repair defects, and the difference between microsatellite-stable (MSS) and microsatellite-unstable HNPCC remains poorly understood. The study was to compare overall copy number variation (CNV) and loss of heterozygosity (LOH) of the entire genome in HNPCCs with MSS and microsatellite-instability (MSI) using the Cytoscan HD Array. This was a study carried out in samples from 20 patients with MSS HNPCC and four patients with MSI HNPCC from the Fudan University Shanghai Cancer Center (China). The microsatellite status was examined using a panel of microsatellite markers. MMR expression status was evaluated by immunohistochemistry. Tumor samples were analyzed with the Genome-Wide Human CytoScan HD Array. CNV and LOH were determined. Fourteen specific CNVs (eight gains: 5p13.1, 7p13, 7q22.3, 8q11.21, 8q12.2, 19q13.11, 20q11.21, and 20q11.23; and six losses: 8p22, 8p23.1, 8p23.1, 17p13.1, 17p13.2, and 18q21.3) were associated with MSS HNPCC. Of these 14 CNVs, gain on 8q12.2 and loss on 17p13.1 were novel. The total length of 8q gains and 20q gains were greater in MSS tumors than in MSI ( P < 0.05). The presence of similar levels of copy-neutral-LOH in MSS (31.7%) and MSI (29.7%) HNPCC suggested that unknown DNA repair genes might be involved in the tumorigenesis of MSS HNPCC. MSS HNPCC is a genetically specific population with increased CNV, which are different from MSI HNPCC. The results may help to clarify the genetic basis of MSS HNPCC tumorigenesis. [ABSTRACT FROM AUTHOR]

Chromosomal instability (CIN) and microsatellite instability (MSI) are two major causes of colorectal cancers. Recently, a percentage of colorectal cancers were found to be neither CIN nor MSI. This study was performed to explore whether microsatellite- and chromosomal-stable (MACS) colorectal cancers comprise a substantially distinct subtype. Sixty-nine sporadic colorectal cancers were classified into three subsets according to ploidy and microsatellite instability status: CIN+, MSI+, and MACS. Clinicopathologic, genetic, and epigenetic differences among these three groups were investigated by immunohistochemical analysis of p53, APC, hMLH1, and BAX and methylation study of p14 ARF , hMLH1, p16 INK4a , MGMT, and MINT1 with methylation-specific polymerase chain reaction. The 69 cases included 49 CIN+, 7 MSI+, and 13 MACS. MACS were found to differ from CIN+ and MSI+ in three aspects. The clinicopathologic features of MACS were similar to MSI+ but distinguished from CIN+. Comparatively, MACS preferred proximal location and poor differentiation ( p < 0.05). An immunohistochemical study demonstrated that MACS had a lower rate of loss of hMLH1 or BAX protein than MSI+ and less loss of APC protein than CIN+. In an epigenetic aspect, both MACS and MSI+ had a high rate of CpG island methylator phenotype (46.2 and 42.9%). However, they differed in the presence of hMLH1 methylation (7.7 vs 57.1%, p < 0.05). Otherwise, compared with CIN+, MACS had a more frequent CpG island methylator phenotype and MINT1 methylation ( p < 0.05) and relatively more common p16 INK4a methylation with marginal significance ( p = 0.056). MACS sporadic colorectal cancers may compose a unique phenotype with distinct clinicopathologic and molecular characteristics. [ABSTRACT FROM AUTHOR]

An early step in the carcinogenesis of hereditary non-polyposis colorectal cancer (HNPCC) and some sporadic colorectal cancers (CRCs) is the acquisition of a 'mutator phenotype' resulting from defects in DNA mismatch repair (MMR) genes, which normally maintain genomic stability. This mutator phenotype causes an approximately 100-1000-fold increase in base substitutions and small insertion/deletion mutations thereby driving carcinogenesis. It also causes genome-wide microsatellite instability (MSI) due to the inability to repair mutations within these small, hard to replicate, repetitive DNA elements. In contrast, less is known about the role of mutator phenotypes in microsatellite stable (MSS) CRC. In this report, we have measured the mutation rates in 11 MSS CRC cell lines to obtain an estimate of the prevalence of mutator phenotypes in MSS carcinogenesis. Of the 11 cell lines, three of them (27%) possess spontaneous hypoxanthine phosphoribosyltransferase mutation rates approximately 10-100-fold above background. When challenged with alkylating and oxidising agents, the degree of survival and apoptotic responses are different, indicating that these cell lines may represent more than one mutator phenotype. These data demonstrate that a significant portion of MSS CRC cell lines has increased mutation rates and that this may play a role in MSS CRC carcinogenesis. [ABSTRACT FROM AUTHOR]

Introduction: Immunotherapy by checkpoint inhibitors, i.e., anti-programmed death-1(PD-1) or anti-programmed death-ligand 1 (PD-L1) antibodies, has gained more attention managing solid tumors. Pembrolizumab (an anti-PD-1 antibody) in metastatic colorectal cancer (CRC) was approved in 2017 by the US FDA.Pembrolizumab is not effective in microsatellite stable, mismatch-repair-proficient (MSS-pMMR) molecular phenotype, which comprises most CRC patients. In this report, we present the first case of metastatic CRC with a dramatic and durable response to pembrolizumab despite being of MSS-pMMR phenotype.A 34-year-old woman, presented seven years ago with T3N2bM0 colon cancer and an appendix carcinoid tumor. The last relapse with bilateral pulmonary metastases was refractory to all treatments. Although it seemed unresponsive to immunotherapy because of MSS molecular phenotype, due to the high expression level of PD-L1 (85%), we started treatment with pembrolizumab 200 mg every three weeks and continued for the overall 19 courses. Surprisingly, a rapid and complete response was observed that last until now, i.e., 17 months after discontinuation of pembrolizumab.Despite non-promising results in the current clinical trials, MSS-pMMR colorectal cancer patients' deprivation from immunotherapy seems not to be reasonable. There are ongoing clinical trials on checkpoint inhibitors either alone or in combination with other drugs. However, immunostaining for PD-L1 should be considered as a possible response predictor.Immunotherapy either by cell-based approaches or by checkpoint inhibitors may revolutionize cancer treatmentPembrolizumab has been approved by the FDA in 2017 for colorectal cancer.However, MSS-pMMR molecular phenotype which comprises the majority of CRC patients, has not shown a good response to checkpoint inhibitors.We present a MSS-pMMR case with complete and durable response to pembrolizumabWe suggest immunostaining for PD-L1 as a possible response predictor to checkpoint inhibitorsReason for the report: Immunotherapy by checkpoint inhibitors, i.e., anti-programmed death-1(PD-1) or anti-programmed death-ligand 1 (PD-L1) antibodies, has gained more attention managing solid tumors. Pembrolizumab (an anti-PD-1 antibody) in metastatic colorectal cancer (CRC) was approved in 2017 by the US FDA.Pembrolizumab is not effective in microsatellite stable, mismatch-repair-proficient (MSS-pMMR) molecular phenotype, which comprises most CRC patients. In this report, we present the first case of metastatic CRC with a dramatic and durable response to pembrolizumab despite being of MSS-pMMR phenotype.A 34-year-old woman, presented seven years ago with T3N2bM0 colon cancer and an appendix carcinoid tumor. The last relapse with bilateral pulmonary metastases was refractory to all treatments. Although it seemed unresponsive to immunotherapy because of MSS molecular phenotype, due to the high expression level of PD-L1 (85%), we started treatment with pembrolizumab 200 mg every three weeks and continued for the overall 19 courses. Surprisingly, a rapid and complete response was observed that last until now, i.e., 17 months after discontinuation of pembrolizumab.Despite non-promising results in the current clinical trials, MSS-pMMR colorectal cancer patients' deprivation from immunotherapy seems not to be reasonable. There are ongoing clinical trials on checkpoint inhibitors either alone or in combination with other drugs. However, immunostaining for PD-L1 should be considered as a possible response predictor.Immunotherapy either by cell-based approaches or by checkpoint inhibitors may revolutionize cancer treatmentPembrolizumab has been approved by the FDA in 2017 for colorectal cancer.However, MSS-pMMR molecular phenotype which comprises the majority of CRC patients, has not shown a good response to checkpoint inhibitors.We present a MSS-pMMR case with complete and durable response to pembrolizumabWe suggest immunostaining for PD-L1 as a possible response predictor to checkpoint inhibitorsCase summary: Immunotherapy by checkpoint inhibitors, i.e., anti-programmed death-1(PD-1) or anti-programmed death-ligand 1 (PD-L1) antibodies, has gained more attention managing solid tumors. Pembrolizumab (an anti-PD-1 antibody) in metastatic colorectal cancer (CRC) was approved in 2017 by the US FDA.Pembrolizumab is not effective in microsatellite stable, mismatch-repair-proficient (MSS-pMMR) molecular phenotype, which comprises most CRC patients. In this report, we present the first case of metastatic CRC with a dramatic and durable response to pembrolizumab despite being of MSS-pMMR phenotype.A 34-year-old woman, presented seven years ago with T3N2bM0 colon cancer and an appendix carcinoid tumor. The last relapse with bilateral pulmonary metastases was refractory to all treatments. Although it seemed unresponsive to immunotherapy because of MSS molecular phenotype, due to the high expression level of PD-L1 (85%), we started treatment with pembrolizumab 200 mg every three weeks and continued for the overall 19 courses. Surprisingly, a rapid and complete response was observed that last until now, i.e., 17 months after discontinuation of pembrolizumab.Despite non-promising results in the current clinical trials, MSS-pMMR colorectal cancer patients' deprivation from immunotherapy seems not to be reasonable. There are ongoing clinical trials on checkpoint inhibitors either alone or in combination with other drugs. However, immunostaining for PD-L1 should be considered as a possible response predictor.Immunotherapy either by cell-based approaches or by checkpoint inhibitors may revolutionize cancer treatmentPembrolizumab has been approved by the FDA in 2017 for colorectal cancer.However, MSS-pMMR molecular phenotype which comprises the majority of CRC patients, has not shown a good response to checkpoint inhibitors.We present a MSS-pMMR case with complete and durable response to pembrolizumabWe suggest immunostaining for PD-L1 as a possible response predictor to checkpoint inhibitorsOutcome: Immunotherapy by checkpoint inhibitors, i.e., anti-programmed death-1(PD-1) or anti-programmed death-ligand 1 (PD-L1) antibodies, has gained more attention managing solid tumors. Pembrolizumab (an anti-PD-1 antibody) in metastatic colorectal cancer (CRC) was approved in 2017 by the US FDA.Pembrolizumab is not effective in microsatellite stable, mismatch-repair-proficient (MSS-pMMR) molecular phenotype, which comprises most CRC patients. In this report, we present the first case of metastatic CRC with a dramatic and durable response to pembrolizumab despite being of MSS-pMMR phenotype.A 34-year-old woman, presented seven years ago with T3N2bM0 colon cancer and an appendix carcinoid tumor. The last relapse with bilateral pulmonary metastases was refractory to all treatments. Although it seemed unresponsive to immunotherapy because of MSS molecular phenotype, due to the high expression level of PD-L1 (85%), we started treatment with pembrolizumab 200 mg every three weeks and continued for the overall 19 courses. Surprisingly, a rapid and complete response was observed that last until now, i.e., 17 months after discontinuation of pembrolizumab.Despite non-promising results in the current clinical trials, MSS-pMMR colorectal cancer patients' deprivation from immunotherapy seems not to be reasonable. There are ongoing clinical trials on checkpoint inhibitors either alone or in combination with other drugs. However, immunostaining for PD-L1 should be considered as a possible response predictor.Immunotherapy either by cell-based approaches or by checkpoint inhibitors may revolutionize cancer treatmentPembrolizumab has been approved by the FDA in 2017 for colorectal cancer.However, MSS-pMMR molecular phenotype which comprises the majority of CRC patients, has not shown a good response to checkpoint inhibitors.We present a MSS-pMMR case with complete and durable response to pembrolizumabWe suggest immunostaining for PD-L1 as a possible response predictor to checkpoint inhibitorsGraphical abstract: Immunotherapy by checkpoint inhibitors, i.e., anti-programmed death-1(PD-1) or anti-programmed death-ligand 1 (PD-L1) antibodies, has gained more attention managing solid tumors. Pembrolizumab (an anti-PD-1 antibody) in metastatic colorectal cancer (CRC) was approved in 2017 by the US FDA.Pembrolizumab is not effective in microsatellite stable, mismatch-repair-proficient (MSS-pMMR) molecular phenotype, which comprises most CRC patients. In this report, we present the first case of metastatic CRC with a dramatic and durable response to pembrolizumab despite being of MSS-pMMR phenotype.A 34-year-old woman, presented seven years ago with T3N2bM0 colon cancer and an appendix carcinoid tumor. The last relapse with bilateral pulmonary metastases was refractory to all treatments. Although it seemed unresponsive to immunotherapy because of MSS molecular phenotype, due to the high expression level of PD-L1 (85%), we started treatment with pembrolizumab 200 mg every three weeks and continued for the overall 19 courses. Surprisingly, a rapid and complete response was observed that last until now, i.e., 17 months after discontinuation of pembrolizumab.Despite non-promising results in the current clinical trials, MSS-pMMR colorectal cancer patients' deprivation from immunotherapy seems not to be reasonable. There are ongoing clinical trials on checkpoint inhibitors either alone or in combination with other drugs. However, immunostaining for PD-L1 should be considered as a possible response predictor.Immunotherapy either by cell-based approaches or by checkpoint inhibitors may revolutionize cancer treatmentPembrolizumab has been approved by the FDA in 2017 for colorectal cancer.However, MSS-pMMR molecular phenotype which comprises the majority of CRC patients, has not shown a good response to checkpoint inhibitors.We present a MSS-pMMR case with complete and durable response to pembrolizumabWe suggest immunostaining for PD-L1 as a possible response predictor to checkpoint inhibitors [ABSTRACT FROM AUTHOR]