微卫星稳定型直肠癌新辅助放化疗联合免疫治疗的研究进展

2015年首次发现高度微卫星不稳定（microsatellite instable-high,MSI-H）/错配修复缺陷（mismatch repair deficiency,dMMR）型结直肠癌对免疫治疗敏感,开启了结直肠癌的免疫治疗时代。然而,微卫星稳定（microsatellite stable,MSS）型结直肠癌对免疫治疗并不敏感。术前新辅助放化疗是目前局部进展期直肠癌（locally advanced rectal cancer,LARC）的标准治疗方式,其临床完全缓解率为20%～30%、病理完全缓解率为5%～44%。为了提高术前新辅助同步放化疗的缓解率,提出通过联合免疫治疗以提高缓解率。2020年在2023年美国临床肿瘤学会年会上,首次展示了新辅助放化疗联合免疫治疗用于治疗MSS型直肠癌的成果。本文旨在回顾近年来MSS型局部进展期直肠癌新辅助放化疗联合免疫治疗的研究进展,并对前景进行展望。     

POLE/POLD1突变在肿瘤免疫治疗预后中的价值

摘 要：免疫检查点抑制剂（immune checkpoint inhibitors,ICIs）已在多种肿瘤中显示出持续的临床疗效。错配修复蛋白缺陷(mismatch repair deficient,dMMR）或微卫星高度不稳定性（microsatellite instability-high,MSI-H）的转移性结直肠癌患者已从免疫治疗中获益。然而,部分PD-L1阴性和微卫星稳定（microsatellite stability,MSS）型结直肠癌患者对免疫治疗也有持续的反应。因此,为了给患者制定最佳治疗方案,选择能够识别免疫检查点阻断疗效的可靠生物标志物,实现精准治疗是至关重要的。DNA聚合酶亚基的关键编码基因POLE/POLD1是除MSI?鄄H和肿瘤突变负荷（tumor mutation burden,TMB）外,最具潜力的免疫治疗预测指标。全文就POLE/POLD1的分子机制及其突变在免疫治疗中的研究进展进行综述。     

MSI-H结直肠癌患者的围手术期免疫治疗进展

结直肠癌是最常见的恶性肿瘤之一，其中DNA错配修复缺陷（mismatch repair-deficient,dMMR）或微卫星高度不稳定（microsatellite instability-high,MSI-H）的结直肠癌患者约占总数的10%～15%。目前，免疫检查点抑制剂（后文简称免疫治疗）已广泛应用于MSI-H/dMMR的转移性结直肠癌患者，但在可切除的局部进展期患者的新辅助治疗以及在Ⅲ期MSI-H/dMMR患者的辅助治疗中的应用尚处于临床研究阶段。本文概述目前免疫治疗在MSI-H/dMMR结直肠癌患者的新辅助治疗及辅助治疗中的相关研究进展，并展望免疫治疗在这类患者中的未来趋势。     

免疫检查点抑制剂联合治疗在微卫星稳定型结直肠癌治疗中的研究进展

结直肠癌是消化系统最常见的恶性肿瘤,发病率在肿瘤中排第3位,死亡率排第2位,对患者的生存期和生活质量造成了严重威胁。免疫检查点抑制剂(ICIs)已成为错配修复缺陷或微卫星高度不稳定(MSI-H/d MMR)结直肠癌的一线及后线治疗方案的重要组成,然而,MSI-H/d MMR结直肠癌仅占所有转移性结直肠癌的4%～5%,且对于微卫星稳定型(MSS)结直肠癌患者,由于肿瘤的异质性和复杂的免疫异质性肿瘤微环境,ICIs单药往往无法克服这些因子而出现应答率不高或出现继发性耐药,因此仅使用单一ICIs基本无效。目前多采用联合治疗策略如抗程序性死亡蛋白受体-1(PD-1)和细胞毒性T淋巴细胞相关蛋白4(CTLA-4)的联合治疗,ICIs联合放疗,ICIs联合细胞外信号调节激酶(MEK)抑制剂和血管内皮生长因子(VEGF)抑制剂,以及ICIs联合溶瘤病毒等提高MSS/错配修复功能完整(pMMR)结直肠癌患者对治疗的应答率。虽然上述联合治疗策略取得不错的近期疗效,在治疗转移性结直肠癌(mCRC)患者中很有前景,但多为单臂小样本探索性研究,数据指向并不完全稳定一致,安全性和有效性还需更多大样本的前瞻性临床...     

免疫检查点抑制剂治疗结直肠癌的疗效及肠道菌群对其疗效影响的研究进展

随着免疫治疗领域的快速发展,越来越多的免疫检查点抑制剂被应用于临床。免疫治疗为结直肠癌晚期转移患者提供了一种新的治疗选择。研究证实,错配修复缺陷/高度微卫星不稳定（dMMR/MSI-H）状态的晚期转移性结直肠癌患者对免疫治疗更敏感,有较为客观及持续的临床反应。在肿瘤免疫治疗的应答中,肠道菌群被证实有一定的调节作用,部分细菌可通过免疫系统或机体代谢功能来影响免疫检查点抑制剂的疗效。随着研究的进展,肠道菌群不仅有望成为结直肠癌免疫治疗的疗效预测性生物标志物,也可能成为影响结直肠癌免疫治疗结果的关键调控因素,在今后的临床治疗中,为更多的晚期结直肠癌患者使用免疫检查点抑制剂获益带来可能性。     

微卫星高度不稳定或错配修复缺陷结直肠癌新辅助免疫治疗的探讨和展望

微卫星高度不稳定（microsatellite instability-high,MSI-H）或错配修复缺陷（mismatch repair-deficient,dMMR）结直肠癌对传统新辅助治疗方案的敏感性较低，免疫治疗的出现改变了MSI-H/dMMR结直肠癌的治疗格局。从晚期疾病的后线治疗到一线治疗，甚至在早期结直肠癌的新辅助治疗，免疫治疗均展现出优异的疗效。全文探讨了结直肠癌新辅助免疫治疗的最新研究进展、目前存在的问题以及未来的发展方向，以期在临床实践过程中为MSI-H/d MMR结直肠癌患者制定个体化治疗方案提供参考。     

免疫检查点抑制剂治疗结直肠癌的研究进展

结直肠癌是常见的消化道恶性肿瘤.免疫检查点抑制剂在肿瘤免疫逃逸中发挥着至关重要的作用,成为抗肿瘤免疫治疗的热点.免疫检查点抑制剂在多种实体瘤的治疗中取得了令人瞩目的效果.在结直肠癌的治疗领域,尤其是针对微卫星不稳定(MSI)和(或)错配修复缺陷(dMMR)的结直肠癌患者,检查点抑制剂亦显示出了良好的疗效及安全性.本文概...     

微卫星稳定型结直肠癌免疫检查点抑制剂疗效预测标志物研究进展

寻找微卫星稳定型结直肠癌免疫检查点抑制剂疗效预测标志物能够使更多的患者从免疫治疗中获益。肿瘤突变负荷（TMB）、POLE/POLD1突变、CMS分型、MGMT甲基化等多个指标具有对微卫星稳定型结直肠癌免疫检查点抑制剂疗效进行预测的潜能和价值。本文通过对微卫星稳定型结直肠癌免疫检查点抑制剂疗效预测标志物的相关研究进行综述,以期为寻找微卫星稳定型结直肠癌患者的最佳治疗策略提供参考。     

结直肠癌肿瘤微环境中M1型巨噬细胞的研究进展

结直肠癌的肿瘤微环境中存在多种类型免疫细胞,其中肿瘤相关巨噬细胞作为重要组成成分,可极化成M1、M2两种不同亚型。M1型巨噬细胞在肿瘤发展过程中主要发挥抑癌作用,M2型巨噬细胞则起促癌作用。高微卫星不稳定（high microsatellite instability,MSI-H）结直肠癌肿瘤微环境中M1型巨噬细胞明显高于微卫星稳定（microsatellite stabilization,MSS）结直肠癌,免疫治疗效果较好。本文主要就M1型巨噬细胞在结直肠癌中的研究进展进行综述,以期为MSI-H结直肠癌免疫治疗提供能多的理论依据和新思路。     

程序性死亡受体1、程序性死亡受体配体1在结直肠癌患者循环肿瘤细胞中的研究进展

近年来,免疫治疗为结直肠癌（CRC）的治疗提供了新的选择。以程序性死亡受体1(PD-1)及其配体程序性死亡受体配体1(PD-L1)为代表的免疫检查点抑制剂在DNA错配修复缺陷（dMMR）/微卫星不稳定（MSI）型CRC的治疗中已取得了显著疗效,尽管如此,只有一小部分CRC患者受益于免疫治疗,如何精准识别受益人群并为其提供个体化治疗成了研究者面临的一大问题。研究表明,肿瘤微环境中的循环肿瘤细胞和免疫细胞等几乎所有成分都可以在外周血中找到,其中循环肿瘤细胞上的PD-1/PD-L1可为CRC的免疫治疗提供指导。本文对CRC患者CTC中PD-1和PD-L1的表达及CRC免疫治疗的研究进展进行综述。     

Recent Advances in the Clinical Development of Immune Checkpoint Blockade Therapy for Mismatch Repair Proficient (pMMR)/non-MSI-H Metastatic Colorectal Cancer

Metastatic colorectal cancer (mCRC) continues to be associated with a poor prognosis, and there remains a significant unmet need for novel agents and treatment regimens. Major breakthroughs have been made with immune checkpoint blockade therapy in several disease types, including DNA mismatch repair deficient/microsatellite instability-high (MSI-H) tumors. To date, however, immune checkpoint monotherapy has not shown significant clinical activity in the treatment of patients with mismatch repair proficient (pMMR)/non-MSI-H mCRC. The immune resistance mechanisms in pMMR/non-MSI-H mCRC have not yet been clearly elucidated. Significant efforts are currently focused on identifying effective combination immunotherapy regimens for the treatment of patients with pMMR/non-MSI-H mCRC. The combination of atezolizumab with cobimetinib had shown promising clinical activity in an early-phase clinical trial. Unfortunately, the IMblaze 370 (COTEZO) phase III trial of atezolizumab/cobimetinib combination in patients with mCRC failed to show significant improvement in overall survival in patients treated with the atezolizumab/combimetinib combination in comparison with regorafenib alone. This review summarizes the recent major advances in the clinical development of immunotherapy regimens for patients with pMMR/non-MSI-H mCRC.     

Chemotherapeutic implications in microsatellite unstable colorectal cancer

Chemotherapy for colorectal cancer is currently offered to patients based on the stage of their cancer, and there is evidence to show an overall survival benefit with 5-fluorouracil-based (5-FU) therapy for patients with lymph node metastasis who receive it. The pathogenesis of colorectal cancer involves genomic instability, with about 15% of tumors demonstrating a form of genomic instability called high-frequency microsatellite instability (MSI-H) and due to loss of DNA mismatch repair function, and the remainder of colorectal tumors lacking MSI-H with retained DNA mismatch repair function and called microsatellite stable (MSS), with a large proportion of these tumors demonstrating another form of genomic instability called chromosomal instability. There is now evidence to show that the form of genomic instability that is present in a patient's colorectal cancer may predict a survival benefit from 5-FU. In particular, patients whose colorectal tumors have MSI-H do not gain a survival benefit with 5-FU as compared to patients with MSS tumors. In vitro evidence supports these findings, as MSI-H colon cancer cell lines are more resistant to 5-FU compared to MSS cell lines. More specifically, components of the DNA mismatch repair system have been shown to recognize and bind to 5-FU that becomes incorporated into DNA and which could be a trigger to induce cell death. The binding and subsequent cell death events would be absent in colorectal tumors with MSI-H, which have lost intact DNA mismatch repair function. These findings suggest that: (a) tumor cytotoxicity of 5-FU is mediated by DNA mechanisms in addition to well-known RNA mechanisms, and (b) patients whose tumors demonstrate MSI-H may not benefit from 5-FU therapy. Future studies should include a better understanding of the cellular mechanisms of the DNA recognition of 5-FU, multi-centered prospective trials investigating the survival benefit of 5-FU based on genomic instability, and the investigation of alternative chemotherapeutic regimens for patients with MSI-H tumors to improve survival.     

Microsatellite Stable Colorectal Cancer With an Immunogenic Phenotype: Challenges in Diagnosis and Treatment

BackgroundPatients with deficient microsatellite mismatch repair (dMMR) colorectal cancer (CRC) may respond to immune checkpoint inhibition (ICI), whereas patients with microsatellite-stable (MSS) CRC have not demonstrated response. However, a proportion of MSS tumors display histomorphologic features characteristic of dMMR tumors consistent with an increased antigenicity. Therefore, a subset of patients with CRC not currently receiving ICI treatment may derive benefit from ICI therapy. We review tumors in which the histologic features suggestive of dMMR were in disagreement with the DNA mismatch repair proteins obtained by immunohistochemistry (IHC). Possible causes of such disagreement are discussed.Materials and MethodsThree patients with CRC suggestive of histomorphologic immunogenicity underwent evaluation by IHC staining for mismatch repair (MMR) status, next-generation sequencing assays, and/or polymerase chain reaction.ResultsFindings compatible with an immunogenic response were similarly observed in all patients. Case 1 highlighted the limiting factors inherent to IHC staining for MMR status: a biopsy initially interpreted as MSS was subsequently interpreted as being dMMR. Case 2 examined the challenges in reconciling histologic characteristics traditionally associated with dMMR CRCs but ultimately determined to be MSS. Case 3 examined the microsatellite instability of CRC resulting from MLH1-methylation and/or MSH6 mutation.ConclusionsWe demonstrated the challenges in establishing MMR status when confronted with conflicting results from histology, IHC, polymerase chain reaction, and next-generation sequencing. Given that dMMR status has been shown to be a biomarker for ICI responsiveness, the importance of accurate identification is critical.     

Challenges and exploration for immunotherapies targeting cold colorectal cancer

In recent years, immune checkpoint inhibitors (ICIs) have made significant breakthroughs in the treatment of various tumors, greatly improving clinical efficacy. As the fifth most common antitumor treatment strategy for patients with solid tumors after surgery, chemotherapy, radiotherapy and targeted therapy, the therapeutic response to ICIs largely depends on the number and spatial distribution of effector T cells that can effectively identify and kill tumor cells, features that are also important when distinguishing malignant tumors from “cold tumors” or “hot tumors”. At present, only a small proportion of colorectal cancer (CRC) patients with deficient mismatch repair (dMMR) or who are microsatellite instability-high (MSI-H) can benefit from ICI treatments because these patients have the characteristics of a “hot tumor”, with a high tumor mutational burden (TMB) and massive immune cell infiltration, making the tumor more easily recognized by the immune system. In contrast, a majority of CRC patients with proficient MMR (pMMR) or who are microsatellite stable (MSS) have a low TMB, lack immune cell infiltration, and have almost no response to immune monotherapy; thus, these tumors are “cold”. The greatest challenge today is how to improve the immunotherapy response of “cold tumor” patients. With the development of clinical research, immunotherapies combined with other treatment strategies (such as targeted therapy, chemotherapy, and radiotherapy) have now become potentially effective clinical strategies and research hotspots. Therefore, the question of how to promote the transformation of “cold tumors” to “hot tumors” and break through the bottleneck of immunotherapy for cold tumors in CRC patients urgently requires consideration. Only by developing an in-depth understanding of the immunotherapy mechanisms of cold CRCs can we screen out the immunotherapy-dominant groups and explore the most suitable treatment options for individuals to improve therapeutic efficacy.     

Molecular profiling of sporadic colorectal tumors by microsatellite analysis

To investigate the prognostic value of multiple genetic alterations, individual molecular tumor profiles were established in 79 sporadic colorectal carcinomas (41 stage II and 38 stage III). Tumors were analyzed for allelic loss (LOH) and genetic instability (MSI) using 14 microsatellites intragenic to or associated with tumor suppressor or DNA mismatch repair genes. Molecular profiling identified tumors with LOH at multiple loci without microsatellite instability (MSS), tumors with high levels of LOH and low level microsatellite marker instability (MSI-L), and tumors with high levels of MSI (MSI-H), but rare LOH. K-ras mutations occurred more frequently in MSS/MSI-L carcinomas (26%) than in MSI-H colorectal tumors (10%), the latter showing a high frequency of TGFbeta type II frameshift mutations (82%). Correlation of molecular and clinical data revealed a better prognosis for stage III tumor patients displaying 5q12 loss rather than retention of heterozygosity. Thus, molecular profiling allows the identification of new prognostic markers and might facilitate the stratification of colorectal cancer patients.     

How to overcome resistance to immune checkpoint inhibitors in colorectal cancer: From mechanisms to translation

Immunotherapy, especially with immune checkpoint inhibitors (ICIs), has shown advantages in cancer treatment and is a new hope for patients who have failed multiline therapy. However, in colorectal cancer (CRC), the benefit is limited to a small subset of patients with microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR) metastatic CRC (mCRC). In addition, 45% to 60% of dMMR/MSI-H mCRC patients showed primary or acquired resistance to ICIs. This means that these patients may have potential unknown pathways mediating immune escape. Almost all mismatch repair-proficient (pMMR) or microsatellite-stable (MSS) mCRC patients do not benefit from ICIs. In this review, we discuss the mechanisms of action of ICIs and their current status in CRC. We then discuss the mechanisms of primary and acquired resistance to ICIs in CRC. Finally, we discuss promising therapeutic strategies to overcome resistance to ICIs in the clinic.     

Frequent Bax frameshift mutations in gastric cancer with high but not low microsatellite instability

Widespread microsatellite instability (MSI) due to the defective DNA mismatch repair underlies the pathogenesis of the majority of hereditary non-polyposis colorectal cancer and a subset of various sporadic malignant tumors. Using 5 microsatellite markers and the criteria of MSI proposed by the National Cancer Institute (NCI) workshop, we analyzed 205 gastric adenocarcinomas for MSI. Based on the number of markers showing instability per tumor, the tumors were divided into three groups; those with two or more of the five markers displaying instability (high MSI, MSI-H), those with one of five markers displaying instability (low MSI, MSI-L), and those with no instability (microsatellite stable, MSS). Among 205 tumors, 30 (15%) were MSI-H, 15 (7%) were MSI-L, and 160 (78%) were MSS. All of the 30 MSI-H tumors demonstrated instability at BAT26, a sensitive marker for the widespread MSI, while none of the 15 MSI-L tumors did. MSI-H tumors were significantly associated with distal location and well or moderate differentiation, but MSI-L tumors were indistinguishable from MSS tumors. Bax frameshift mutations were detected in 60% of the 30 MSI-H tumors, while not in any of the 15 MSI-L tumors. These results suggest that microsatellite analysis using the criteria proposed by the NCI workshop may be appropriate for gastric cancers because it unveils real differences in genotype and phenotype.     

Mechanism of carcinogenesis in familial tumors

It is thought that malignant tumors occur through interactions of multiple environmental factors and a personal genetic factor. A normal somatic cell having an intrinsic function is able to acquire the characteristics of a malignant cell under the influence of many factors. A small percentage of all tumors have obvious familial aggregation. These entities are called familial cancer. The familial cancer syndrome is well defined for colorectal cancer, breast cancer, endocrine neoplasia, and so on. Traits of familial tumors are sequentially inherited by offspring through gametes in a Mendelian fashion, most commonly in an autosomal-dominant manner. Carcinogenesis requires multiple genetic events. A patient with a familial tumor is ahead of an individual without any germline mutation in the carcinogenesis process. In such a situation, patients frequently suffer from multiple malignant tumors at a young age. It is well known that three major genes are closely related to the cell cycle and tumorigenesis. These gene types are protooncogenes, tumor suppressor genes, and DNA mismatch repair genes. Proto-oncogenes function to accelerate cells during the G₁ or growth phase of the cell cycle. Tumor suppressor genes act as blocks against cell growth and proliferation. Inactivation of tumor suppressor genes requires alterations in both alleles. These phenomena are known as Knudsons two-hits theory. However, DNA mismatch repair genes are known as caretaker genes and correct mismatch pair generation during DNA replication. Germline mutation of DNA mismatch repair genes causes hereditary nonpolyposis colorectal cancer. The tumor phenotype from patients with hereditary nonpolyposis colorectal cancer is demonstrated to be microsatellite instability positive.     

Complete pathological response after chemotherapy or immune checkpoint inhibitors in deficient MMR metastatic colorectal cancer: Results of a retrospective multicenter study

About 5% of the patients with metastatic colorectal cancers (mCRC) present microsatellite instability (MSI)/deficient mismatch repair system (dMMR). While metastasectomy is known to improve overall and progression-free survival in mCRC, specific results in selected patients with dMMR/MSI mCRC are lacking. Our study aimed to describe metastasectomy results, characterize histological response and evaluate pathological complete response (pCR) rate in patients with dMMR/MSI mCRC. We retrospectively reviewed data from all consecutive patients with dMMR/MSI mCRC who underwent surgical metastasectomy between January 2010 and June 2021 in 17 French centers. Primary outcome was to assess the pCR rate defined by tumor regression grade (TRG) 0. Secondary endpoints included relapse-free survival (RFS) and overall survival (OS), and explored TRG as predictive factor for RFS and OS. Among the 88 patients operated, 109 metastasectomies were performed in 81 patients after neoadjuvant treatment [chemotherapy ± targeted therapy (CTT): 69, 85.2%; immunotherapy (ICI): 12, 14.8%], and pCR was achieved in 13 (16.1%) patients. Among the latter, pCR rate were 10.2% in the patients having received CTT (N = 7) and 50.0% in the patients treated with ICI (N = 6). Radiological response did not predict TRG. With a median follow-up of 57.9 (IQR 34.2-81.6) months, median RFS was 20.2 (15.4-not reached) months, median OS was not reached. Major pathological responses (TRG0 + TRG1) were significantly associated with longer RFS (HR 0.12, 95% CI 0.03-0.55; P = .006). The pCR rate of 16.1% achieved with neoadjuvant treatment in patients with dMMR/MSI mCRC is consistent with previously reported rates in pMMR/MSS mCRC. Immunotherapy showed better pCR rate than chemotherapy ± targeted therapy. Further prospective trials are needed to validate immunotherapy as neoadjuvant treatment in resectable/potentially resectable dMMR/MSI mCRC and identify predictive factors for pCR.     

结直肠癌免疫检查点抑制剂治疗相关预测性标志物的研究进展

以免疫检查点抑制剂（immune checkpoint inhibitors,ICIs）为代表的免疫疗法开辟了肿瘤治疗的新纪元。目前ICIs已经广泛应用于晚期转移性结直肠癌患者的治疗。预测性标志物是精确筛选可从ICIs治疗中受益的患者群体的重要工具。本文回顾并总结了目前ICIs治疗结直肠癌重要的预测性标志物及其研究现状,包括错配修复缺陷及微卫星不稳定性、肿瘤突变负荷、DNA聚合酶ε/DNA聚合酶δ1以及PD-L1表达等。通过了解这些标志物对于结直肠癌ICIs治疗的响应及患者预后的预测价值,有助于指导临床医生筛选潜在获益人群,提高治疗效率,实现精准化治疗。