Immunotherapy in the neoadjuvant treatment of gastrointestinal tumors: is the time ripe?

Immune checkpoint inhibitors (ICIs) revolutionized the management of mismatch repair-deficient (dMMR)/microsatellite instability-high (MSI-H) gastrointestinal (GI) cancers. Based on notable results observed in the metastatic setting, several clinical trials investigated ICIs as neoadjuvant treatment (NAT) for localized dMMR/MSI-H GI cancers, achieving striking results in terms of clinical and pathological responses and creating the opportunity to spare patients from neoadjuvant chemotherapy and/or radiotherapy and even surgical resection. Nevertheless, these impressive findings are mainly derived from small proof of concept phase II studies and there are still several open questions to address. Moreover, dMMR/MSI-H represents a limited subgroup accounting for less than 10% of GI cancers. Consequently, many efforts have been produced to investigate neoadjuvant ICIs also in mismatch repair-proficient/microsatellite stable (MSS) cancers, considering the potential synergistic effect in combining immune-targeted agents with standard therapies such as chemo and/or radiotherapy. However, results for combining ICIs to the standard of care in the unselected population are still unsatisfactory, without improvements in event-free survival in esophago-gastric adenocarcinoma for the addition of pembrolizumab to chemotherapy, and sometimes limited benefit in patients with locally advanced rectal cancer. Therefore, a major challenge will be to identify among the heterogenous spectrum of this disease, those patients that could take advantage of neoadjuvant immunotherapy and deliver the most effective treatment. In this review we discuss the rationale of NAT in GI malignancies, summarize the available evidence regarding the completed trials that evaluated this treatment strategy in both MSI-H and MSS tumors. Finally, we discuss ongoing studies and future perspectives to render neoadjuvant immunotherapy another arrow in the quiver for the treatment of locally advanced GI tumors.

Advancing Personalized Medicine in the Treatment of Locally Advanced Rectal Cancer

Rectal cancer presents a significant burden globally, often requiring multimodal therapy for locally advanced cases. Long-course chemoradiotherapy (LCRT) and short-course radiotherapy (SCRT) followed by surgery have been conventional neoadjuvant approaches. Recent trials favor LCRT due to improved local control. However, distant tumor recurrence remains a concern, prompting the exploration of total neoadjuvant therapy (TNT) as a comprehensive treatment strategy. Immune checkpoint inhibitors (ICIs) show promise, particularly in mismatch repair-deficient (dMMR) or microsatellite instability-high (MSI-H) tumors, potentially revolutionizing neoadjuvant regimens. Nonoperative management (NOM) represents a viable alternative post-neoadjuvant therapy for selected patients achieving complete clinical response (cCR). Additionally, monitoring minimal residual disease (MRD) using circulating tumor DNA (ctDNA) emerges as a non-invasive method for the assessment of treatment response. This review synthesizes current evidence on TNT, ICIs, NOM, and ctDNA, elucidating their implications for rectal cancer management and highlighting avenues for future research and clinical application.

Treatment strategies and molecular mechanism of radiotherapy combined with immunotherapy in colorectal cancer

Radiotherapy (RT) remodels the tumor immune microenvironment (TIME) and modulates the immune response to indirectly destroy tumor cells, in addition to directly killing tumor cells. RT combined with immunotherapy may significantly enhance the efficacy of RT in colorectal cancer by modulating the microenvironment. However, the molecular mechanisms by which RT acts as an immunomodulator to modulate the immune microenvironment remain unclear. Further, the optimal modalities of RT combined with immunotherapy for the treatment of colorectal cancer, such as the time point of combining RT and immunization, the fractionation pattern and dosage of radiotherapy, and other methods to improve the efficacy, are also being explored parallelly. To address these aspects, in this review, we summarized the mechanisms by which RT modulates TIME and concluded the progress of RT combined with immunization in preclinical and clinical trials. Finally, we discussed heavy ion radiation therapy and the efficacy of prediction markers and other immune combination therapies. Overall, combining RT with immunotherapy to enhance antitumor effects will have a significant clinical implication and will help to facilitate individualized treatment modalities.

The next bastion to be conquered in immunotherapy: microsatellite stable colorectal cancer

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths worldwide, and its incidence continues to rise, particularly in developing countries. The advent of immune checkpoint inhibitors (ICIs) has represented a significant advancement in CRC treatment. Deficient mismatch repair (dMMR) or high microsatellite instability (MSI-H) serves as a biomarker for immunotherapy, with dMMR/MSI-H CRC exhibiting significantly better response rates to immunotherapy compared to proficient mismatch repair (pMMR)or microsatellite stable (MSS) CRC. While some progress has been made in the treatment of pMMR/MSS CRC in recent years, it remains a challenging issue in clinical practice. The tumor microenvironment (TME) plays a crucial role not only in the development and progression of CRC but also in determining the response to immunotherapy. Understanding the characteristics of the TME in pMMR/MSS CRC could offer new insights to enhance the efficacy of immunotherapy. In this review, we provide an overview of the current research progress on the TME characteristics and advancements in immunotherapy for pMMR/MSS CRC.

Radiotherapy in the preoperative neoadjuvant treatment of locally advanced rectal cancer

Radiotherapy and chemotherapy are effective treatments for patients with locally advanced rectal cancer (LARC) and can significantly improve the likelihood of R0 resection. Radiotherapy can be used as a local treatment to reduce the size of the tumor, improve the success rate of surgery and reduce the residual cancer cells after surgery. Early chemotherapy can also downgrade the tumor and eliminate micrometastases throughout the body, reducing the risk of recurrence and metastasis. The advent of neoadjuvant concurrent radiotherapy (nCRT) and total neoadjuvant treatment (TNT) has brought substantial clinical benefits to patients with LARC. Even so, given increasing demand for organ preservation and quality of life and the disease becoming increasingly younger in its incidence profile, there is a need to further explore new neoadjuvant treatment options to further improve tumor remission rates and provide other opportunities for patients to choose watch-and-wait (W&W) strategies that avoid surgery. Targeted drugs and immunologic agents (ICIs) have shown good efficacy in patients with advanced rectal cancer but have not been commonly used in neoadjuvant therapy for patients with LARC. In this paper, we review several aspects of neoadjuvant therapy, including radiation therapy and chemotherapy drugs, immune drugs and targeted drugs used in combination with neoadjuvant therapy, with the aim of providing direction and thoughtful perspectives for LARC clinical treatment and research trials.

Current progress of immune checkpoint inhibitors for advanced colorectal cancer: concentrating on the efficacy improvement

Immune checkpoint inhibitors (ICIs) have paved a new pathway and revolutionized cancer treatment. Currently, ICIs have been extensively used for patients with advanced colorectal cancer (CRC), especially those harboring microsatellite instability (MSI). However, the efficacy of ICIs varies tremendously in different individuals, and some patients may not benefit from ICIs, which limits their clinical application. How to improve the efficacy of ICIs is an important issue to be solved. On the one hand, it is urgent to discover the predictive biomarkers to accurately screen the patients who gain benefit from ICIs, like microsatellite stability, tumor mutation burden (TMB), DNA polymerase ε/DNA polymerase δ1 mutations, and the expression of programmed death-ligand 1 (PD-L1). The rational use of these biomarkers will help clinicians identify suitable candidates who will benefit from ICI treatment, thereby improving therapeutic efficiency. Additionally, it is vital to design combination therapeutic strategies for optimizing the therapeutic effectiveness of ICIs. Nowadays, treatment strategies like chemotherapy, radiotherapy, targeted therapy along with ICIs, have helped improve the therapeutic effectiveness of ICIs. In this review, we have focused on the recent advancements in the predictive biomarkers and combination therapeutic strategies with ICIs for colorectal cancer.

Perioperative immune checkpoint inhibition for colorectal cancer: recent advances and future directions

For colorectal cancer (CRC), surgical resection remains essential for achieving good prognoses. Unfortunately, numerous patients with locally advanced CRC and metastatic CRC failed to meet surgical indications or achieve pathological complete response after surgery. Perioperative therapy has been proven to effectively lower tumor staging and reduce recurrence and metastasis. Immune checkpoint inhibitors (ICIs) have shown unprecedented prolongation of survival time and satisfactory safety in patients with high microsatellite instability/deficient mismatch repair (MSI-H/dMMR), while the therapeutic effect obtained by patients with mismatch repair-proficient or microsatellite stable (pMMR/MSS) was considered minimal. However, recent studies found that certain CRC patients with dMMR/MSI-H presented intrinsic or acquired immune resistance, and pMMR/MSS CRC patients can also achieve better efficacy. Therefore, more predictors are required for screening patients with potential clinical benefits. Since the discovery of synergistic effects between immunotherapy, chemotherapy, and radiotherapy, different immunotherapy-based therapies have been applied to the perioperative therapy of CRC in an increasing number of research. This review comprehensively summarized the past and current progress of different combinations of immunotherapy in perioperative clinical trials for CRC, focusing on the efficacy and safety, and points out the direction for future development.

Immunocheckpoint Inhibitors in Microsatellite-Stable or Proficient Mismatch Repair Metastatic Colorectal Cancer: Are We Entering a New Era?

Colorectal cancer (CRC) is the third most frequent cancer and the second leading cause of cancer-related deaths in Europe. About 5% of metastatic CRC (mCRC) are characterized by high microsatellite instability (MSI) due to a deficient DNA mismatch repair (dMMR), and this condition has been related to a high sensitivity to immunotherapy, in particular to the Immune Checkpoint Inhibitors (ICIs). In fact, in MSI-H or dMMR mCRC, treatment with ICIs induced remarkable response rates and prolonged survival. However, the majority of mCRC cases are mismatch-repair-proficient (pMMR) and microsatellite-stable (MSS), and unfortunately these conditions involve resistance to ICIs. This review aims to provide an overview of the strategies implemented to overcome ICI resistance and/or define subgroups of patients with MSS or dMMR mCRC who may benefit from immunotherapy.

Phase II study of capecitabine-based concomitant chemoradiation followed by durvalumab as a neoadjuvant strategy in locally advanced rectal cancer: the PANDORA trial

BACKGROUND

This study investigated the efficacy of chemoradiotherapy (CRT) followed by durvalumab as neoadjuvant therapy of locally advanced rectal cancer.

PATIENTS AND METHODS

The PANDORA trial is a prospective, phase II, open-label, single-arm, multicenter study aimed at evaluating the efficacy and safety of preoperative treatment with durvalumab (1500 mg every 4 weeks for three administrations) following long-course radiotherapy (RT) plus concomitant capecitabine (5040 cGy RT in 25-28 fractions over 5 weeks and capecitabine administered at 825 mg/m2 twice daily). The primary endpoint was the pathological complete response (pCR) rate; secondary endpoints were the proportion of clinical complete remissions and safety. The sample size was estimated assuming a null pCR proportion of 0.15 and an alternative pCR proportion of 0.30 (α = 0.05, power = 0.80). The proposed treatment could be considered promising if ≥13 pCRs were observed in 55 patients (EudraCT: 2018-004758-39; NCT04083365).

RESULTS

Between November 2019 and August 2021, 60 patients were accrued, of which 55 were assessable for the study's objectives. Two patients experienced disease progression during treatment. Nineteen out of 55 eligible patients achieved a pCR (34.5%, 95% confidence interval 22.2% to 48.6%). Regarding toxicity related to durvalumab, grade 3 adverse events (AEs) occurred in four patients (7.3%) (diarrhea, skin toxicity, transaminase increase, lipase increase, and pancolitis). Grade 4 toxicity was not observed. In 20 patients (36.4%), grade 1-2 AEs related to durvalumab were observed. The most common were endocrine toxicity (hyper/hypothyroidism), dermatologic toxicity (skin rash), and gastrointestinal toxicity (transaminase increase, nausea, diarrhea, constipation).

CONCLUSION

This study met its primary endpoint showing that CRT followed by durvalumab could increase pCR with a safe toxicity profile. This combination is a promising, feasible strategy worthy of further investigation.

From organ preservation to selective surgery: How immunotherapy changes colorectal surgery?

The emergence of immunotherapy has revolutionized the traditional treatment paradigm of colorectal cancer (CRC). Among them, immune checkpoint blockade has become the first-line treatment for metastatic colorectal cancer (mCRC) and has made significant progress in the treatment of locally advanced colorectal cancer (LACRC). We reviewed a series of clinical trials that have made breakthrough progress. We will emphasize the breakthrough progress in achieving organ preservation in patients with high microsatellite instability or DNA mismatch repair deficiency (MSI-H/dMMR), and based on this, we propose the concept of selective surgery, which includes selectively removing or preserving lymph nodes, with the aim of proving our idea through more research in the future.

New Opportunities for Minimizing Toxicity in Rectal Cancer Management

Advances in multimodal management of locally advanced rectal cancer (LARC), consisting of preoperative chemotherapy and/or radiotherapy followed by surgery with or without adjuvant chemotherapy, have improved local disease control and patient survival but are associated with significant risk for acute and long-term morbidity. Recently published trials, evaluating treatment dose intensification via the addition of preoperative induction or consolidation chemotherapy (total neoadjuvant therapy [TNT]), have demonstrated improved tumor response rates while maintaining acceptable toxicity. In addition, TNT has led to an increased number of patients achieving a clinical complete response and thus eligible to pursue a nonoperative, organ-preserving, watch and wait approach, thereby avoiding toxicities associated with surgery, such as bowel dysfunction and stoma-related complications. Ongoing trials using immune checkpoint inhibitors in patients with mismatch repair-deficient tumors suggest that this subgroup of patients with LARC could potentially be treated with immunotherapy alone, sparing them the toxicity associated with preoperative treatment and surgery. However, the majority of rectal cancers are mismatch repair-proficient and less responsive to immune checkpoint inhibitors and require multimodal management. The synergy noted in preclinical studies between immunotherapy and radiotherapy on immunogenic tumor cell death has led to the design of ongoing clinical trials that explore the benefit of combining radiotherapy, chemotherapy, and immunotherapy (mainly of immune checkpoint inhibitors) and aim to increase the number of patients eligible for organ preservation.

Developments in Checkpoint Inhibitor Therapy for the Management of Deficient Mismatch Repair (dMMR) Rectal Cancer

Deficient mismatch repair (dMMR)/microsatellite instability-high (MSIH) colorectal cancer is resistant to conventional chemotherapy but responds to immune checkpoint inhibition (ICI). We review the standard of care in locally advanced dMMR rectal cancer with a focus on ICI. We also present a case report to highlight the treatment complexities and unique challenges of this novel treatment approach. ICI can lead to immune related adverse events (irAEs), resulting in early treatment discontinuation as well as new challenges to surveillance and surgical management. Overall, neoadjuvant ICI can lead to robust treatment responses, but its impact on durable response and organ preservation requires further study.

Emerging evidence of immunotherapy for colorectal cancer

Since the advent of immune checkpoint inhibitors, which modulate the interplay between the tumor cell and immune system, immunotherapy has become widely recognized as a new standard treatment for cancers including microsatellite instability-high (MSI-H) colorectal cancer. Immune checkpoint inhibitors such as pembrolizumab and nivolumab (anti-PD-1 antibodies) that act in the effector phase of T cells and ipilimumab (anti-CTLA-4 antibody) that acts mainly in the priming phase are now in clinical use. These antibodies have shown therapeutic efficacy in MSI colorectal cancer patients who have failed to respond to existing standard therapies. Pembrolizumab is also strongly recommended as first-line therapy for MSI-H metastatic colorectal cancer. Therefore, the MSI status and tumor mutation burden of the tumor should be clarified before starting treatment. Because many patients do not respond to immune checkpoint inhibitors, combination therapies with immune checkpoint inhibitors, including chemotherapy, radiotherapy, or molecularly targeted agents, are being investigated. Furthermore, treatment methods for preoperative adjuvant therapy for rectal cancer are being developed.

Implications of recent neoadjuvant clinical trials on the future practice of radiotherapy in locally advanced rectal cancer

Over the last two decades, the standard treatment for locally advanced rectal cancer (LARC) has been neoadjuvant chemoradiotherapy plus total mesorectal excision followed by adjuvant chemotherapy. Total neoadjuvant treatment (TNT) and immunotherapy are two major issues in the treatment of LARC. In the two latest phase III randomized controlled trials (RAPIDO and PRODIGE23), the TNT approach achieved higher rates of pathologic complete response and distant metastasis-free survival than conventional chemoradiotherapy. Phase I/II clinical trials have reported promising response rates to neoadjuvant (chemo)-radiotherapy combined with immunotherapy. Accordingly, the treatment paradigm for LARC is shifting toward methods that increase the oncologic outcomes and organ preservation rate. However, despite the progress of these combined modality treatment strategies for LARC, the radiotherapy details in clinical trials have not changed significantly. To guide future radiotherapy for LARC with clinical and radiobiological evidence, this study reviewed recent neoadjuvant clinical trials evaluating TNT and immunotherapy from a radiation oncologist’s perspective.

Interim result of phase II, prospective, single-arm trial of long-course chemoradiotherapy combined with concurrent tislelizumab in locally advanced rectal cancer

Background

Neoadjuvant chemoradiotherapy is the standard treatment for locally advanced rectal cancer, with modest benefits on tumor regression and survival. Since chemoradiotherapy combined with immune checkpoint inhibitors has been reported to have synergic effects. This study aims to explore the safety and efficacy of long-course chemoradiotherapy combined with concurrent tislelizumab as a neoadjuvant treatment regimen for patients with locally advanced rectal cancer.

Methods

This manuscript reported the interim result of a prospective, multicenter, single-arm, phase II trial. Patients with mid-to-low locally advanced rectal cancer with clinical stages of cT3-4a N0M0 or cT1-4a N1-2M0 were included. The patients received long-course radiotherapy (50 Gy/25 f, 2 Gy/f, 5 days/week) and three 21-day cycles of capecitabine (1000 mg/m2, bid, day1-14) plus concurrent three 21-day cycles of tislelizumab (200 mg, day8), followed by a radical surgery 6-8 weeks after radiotherapy. The primary endpoint was the pathological complete response rate. (Clinical trial number: NCT04911517).

Results

A total of 26 patients completed the treatment protocol between April 2021 and June 2022. All patients completed chemoradiotherapy, 24 patients received three cycles of tislelizumab, and 2 patients received two cycles. The pathological complete remission (ypT0N0) was achieved in 50% (13/26) of the patients with all proficient mismatch repair tumors. The immune-related adverse event occurred in 19.2% (5/26) of patients. Patients with no CEA elevation or age less than 50 were more likely to benefit from this treatment regimen.

Conclusion

Long-course chemoradiotherapy combined with concurrent tislelizumab in patients with locally advanced low rectal cancer had favorable safety and efficacy, and does not increase the complication rate of surgery. Further study is needed to confirm these results.

Immunotherapy combined with radiotherapy to reverse immunosuppression in microsatellite stable colorectal cancer

In recent years, the exploration of immune checkpoint inhibitors (ICIs) has resulted in substantial progress and has changed the pattern of cancer treatment. ICIs have revolutionized the treatment landscape of microsatellite instable colorectal cancer while the efficacy is very limited in patients with microsatellite stable colorectal cancer. Therefore, sensitizing MSS CRC to immunotherapy is a major challenge in the field of CRC immunotherapy. Immunotherapy-based combination therapy is an effective strategy. This review of radiotherapy (RT) as a local treatment has dramatically changed in recent years, and it is now widely accepted that RT can deeply reshape the tumor environment by modulating the immune response. Such evidence gives a strong rationale for the synergism of radiotherapy and immunotherapy, introducing the era of 'immunoradiotherapy'. How to give full play to the synergistic effect of radiotherapy and immunotherapy to improve the therapeutic effect of MSS CRC and bring good prognosis is a hot problem to be solved in the field of cancer treatment.This article reviews the development of CRC immunotherapy, the immune resistance mechanism of MSS CRC, and the impact and potential value of immunotherapy combined with radiotherapy on the immune environment of CRC.

Immune Checkpoint Inhibitor-Based Combination Therapy for Colorectal Cancer: An Overview

Colorectal cancer (CRC) is one of the most common diseases in the world. Tumor immunotherapy is an innovative cancer treatment that acts by activating the human body's autoimmune system. Immune checkpoint block has been shown to be effective in DNA deficient mismatch repair/microsatellite instability-high CRC. However, the therapeutic effect for proficient mismatch repair/microsatellite stability patients still requires further study and optimization. At present, the main CRC strategy is to combine other therapeutic methods, such as chemotherapy, targeted therapy, and radiotherapy. Here, we review the current status and the latest progress of immune checkpoint inhibitors in the treatment of CRC. At the same time, we consider therapeutic opportunities for transforming cold to hot, as well as perspectives on possible future therapies, which may be in great demand for drug-resistant patients.

Total neoadjuvant treatment and PD-1/PD-L1 checkpoint inhibitor in locally advanced rectal cancer

For local advanced rectal cancer (LARC), total neoadjuvant treatment (TNT) has shown more complete response (CR), reduced risk of distant metastasis (DM) and increase of the sphincter preservation rate. Now it is the one and only recommendation for high-risk group of LARC according to National Comprehensive Cancer Network (NCCN) rectal cancer guideline, while it is also preferentially recommended for low-risk group of LARC. TNT is also beneficial for distant rectal cancer patients who have need for organ preservation. Even though the prognostic value of programmed cell death-ligand 1 (PD-L1) in the neoadjuvant chemoradiotherapy (NACRT) of LARC patients is undetermined yet, the combination of NACRT and programmed cell death-1 (PD-1)/PD-L1 antibodies seem bring new hope for mismatch repair proficient (pMMR)/microsatellite stable (MSS) LARC patients. Accumulating small sample sized studies have shown that combining NACRT with PD-1/PD-L1 antibody yield better short-term outcomes for pMMR/MSS LARC patients than historic data. However, ideal total dose and fractionation of radiotherapy remains one of unresolved issues in this combination setting. Thorough understanding the impact of radiotherapy on the tumor microenvironment and their interaction is needed for in-depth understanding and exquisite design of treatments combination model.

Strategies to Optimize Treatment for Locally Advanced Rectal Cancer

Neoadjuvant long-course concurrent chemoradiation plus surgery, followed by optional adjuvant chemotherapy, is a standard of care for locally advanced rectal cancer (LARC). However, this traditional approach has several limitations, including low pathological complete response (pCR) (10-25%), high metastasis rate (30-35%), and highly inconsistent compliance with adjuvant chemotherapy (25-75%). Treatment modalities for LARC have dramatically evolved in recent years. Multiple clinical trials have focused on optimizing strategies to achieve a win-win situation for oncologic outcomes and functions. Here, we review the latest studies into optimizing neoadjuvant treatment for LARC.

Clinicopathological characteristics of high microsatellite instability/mismatch repair-deficient colorectal cancer: A narrative review

Colorectal cancers (CRCs) with high microsatellite instability (MSI-H) and deficient mismatch repair (dMMR) show molecular and clinicopathological characteristics that differ from those of proficient mismatch repair/microsatellite stable CRCs. Despite the importance of MSI-H/dMMR status in clinical decision making, the testing rates for MSI and MMR in clinical practice remain low, even in high-risk populations. Additionally, the real-world prevalence of MSI-H/dMMR CRC may be lower than that reported in the literature. Insufficient MSI and MMR testing fails to identify patients with MSI-H/dMMR CRC, who could benefit from immunotherapy. In this article, we describe the current knowledge of the clinicopathological features, molecular landscape, and radiomic characteristics of MSI-H/dMMR CRCs. A better understanding of the importance of MMR/MSI status in the clinical characteristics and prognosis of CRC may help increase the rates of MMR/MSI testing and guide the development of more effective therapies based on the unique features of these tumors.

Immunogenic Cell Death: An Emerging Target in Gastrointestinal Cancers

Immunogenic cell death (ICD) is a regulated form of cell death that induces the activation of both innate and adaptive immune responses through the release of damage-associated molecular patterns (DAMPs) and their subsequent recognition by pattern-recognition receptors (PRRs), generating specific CD8+ T lymphocytes. Thus, ICD inducers (such as certain chemotherapeutic agents, targeted therapies, radiation, and oncolytic viruses) could become a potential cancer treatment by providing antitumour immunity and cancer vaccination. Moreover, their combination with immunotherapy, especially with immune checkpoint inhibitors, could overcome the immunosuppressive tumour microenvironment that characterises certain cancers, including gastrointestinal cancers. This review will provide insights into the role of ICD induction in colorectal, gastric, pancreatic, and hepatocellular carcinomas. Specifically, we will discuss the main mechanisms involved in ICD, their potential application in gastrointestinal cancer treatment, and the latest clinical trial updates.

The Evolving Landscape of Immunotherapy in Locally Advanced Rectal Cancer Patients

Simple Summary

At the last 2022 annual ASCO meeting, impressive results of anti-PD1 activity in clinical stage 2 and 3 microsatellite instable rectal cancer patients have been published. Moreover, a growing number of studies assessed the synergism between neoadjuvant (chemo)radiotherapy and immunotherapy in microsatellite stable localized rectal cancer patients. Major findings of immunotherapy activity and efficacy in localized rectal cancer, according to microsatellite status, are discussed in this commentary.

Abstract

Standard treatments of localized rectal cancer are surgery or the multimodal approach with neoadjuvant treatments (chemo-radiotherapy, short-course radiotherapy, induction, or consolidation chemotherapy) followed by surgery. In metastatic colorectal cancer (mCRC), immune checkpoint inhibitors (ICIs) are now the first choice in patients with a deficient mismatch repair system/microsatellite instability (dMMR/MSI-H) and are being explored in combination with chemotherapy to rewire the immune system against malignant cells in subjects with proficient mismatch repair system/microsatellite low (pMMR/MSI-L) cancers, with promising signals of efficacy. Recently, some efforts have been made to translate ICIs in earlier stages of CRC, including localized rectal cancer, with breakthrough efficacy and an organ preservation rate of mono-immunotherapy in dMMR/MSI-H patients and promising anti-tumor activity of immunotherapy plus neoadjuvant (chemo)radiotherapy in pMMR/MSI-L subjects. Here, we present the rationale, results, and limitations of the most remarkable trials assessing ICIs in dMMR/MSI-H and pMMR/MSI-L localized rectal cancer patients, at the same time highlighting the most promising research perspectives that have followed these studies.

Neoadjuvant Immunotherapy in Gastrointestinal Cancers - The New Standard of Care?

The development of immune checkpoint inhibitors (ICI) offers novel treatment possibilities for solid cancers, with the crucial benefit of providing higher cure rates. These agents have become part of standard treatments in the metastatic and adjuvant setting for select cancers, such as melanoma, non-small cell lung cancer (NSCLC) or urological malignancies. Currently, there is ample clinical interest in employing ICI in a neoadjuvant setting with a curative intent. This approach is especially supported by the scientific rationale that ICI primarily stimulate the host immune system to eradicate tumor cells, rather than being inherently cytotoxic. Aside from tumor downstaging, neoadjuvant immunotherapy offers the potential of an in situ cancer vaccination, leading to a systemic adjuvant immunological effect after tumor resection. Moreover, preclinical data clearly demonstrate a synergistic effect of ICI with radiotherapy (RT), chemoradiotherapy (CRT) or chemotherapy (ChT). This review harmonizes preclinical concepts with real world data (RWD) in the field of neoadjuvant ICI in gastrointestinal (GI) cancers and discusses their limitations. We believe this is a crucial approach, since up to now, neoadjuvant strategies have been primarily developed by clinicians, whereas the advances in immunotherapy primarily originate from preclinical research. Currently there is limited published data on neoadjuvant ICI in GI cancers, even though neoadjuvant treatments including RT, CRT or ChT are frequently employed in locally advanced/oligometastatic GI cancers (i.e. rectal, pancreatic, esophagus, stomach, etc.). Utilizing established therapies in combination with ICI provides an abundance of opportunities for innovative treatment regimens to further improve survival rates.

The Multimodal Management of Locally Advanced Rectal Cancer: Making Sense of the New Data

In the past 40 years, the treatment of locally advanced rectal cancer has evolved with the addition of radiotherapy or chemoradiotherapy and providing (neo)adjuvant systemic chemotherapy to major surgery. However, recent trends have focused on improving our ability to risk-stratify patients and tailoring treatment to achieve the best oncologic outcome while limiting the impact on long-term quality of life. Therefore, there has been increasing interest in pursuing a watch-and-wait approach to achieve organ preservation. Several retro- and prospective studies suggest safety of the watch-and-wait approach, though it is still considered controversial due to limited clinical evidence, concerns about tumor regrowth, and subsequent distant progression. To further reduce treatment, MRI risk stratification, together with patient characteristics and patient preferences, can guide personalized treatment and reserve radiation and chemotherapy for a select patient population. Ultimately, improved options for reassessment during neoadjuvant treatment may allow for more adaptive therapy options based on treatment response. This article provides an overview of some major developments in the multimodal treatment of locally advanced rectal cancer. It reviews some relevant, controversial issues of the watch-and-wait approach and opportunities to personally tailor and reduce treatment. It also reviews the overall neoadjuvant treatment, including total neoadjuvant therapy trials, and how to best optimize for a potential complete response. Finally, it provides an algorithm as an example of how such a personalized, tailored, adaptive, and reduced treatment could look like in the future.

Neoadjuvant Immunotherapy for MSI-H/dMMR Locally Advanced Colorectal Cancer: New Strategies and Unveiled Opportunities

Patients with locally advanced colorectal cancer (LACRC) have a high risk of recurrence and metastasis, although neoadjuvant therapy may provide some benefit. However, patients with high microsatellite instability/deficient mismatch repair (MSI-H/dMMR) LACRC receive little benefit from neoadjuvant chemoradiotherapy (nCRT) or neoadjuvant chemotherapy (nCT). The 2015 KEYNOTE-016 trial identified MSI-H/dMMR as a biomarker indicative of immunotherapy efficacy, and pointed to the potential use of immune checkpoint inhibitors (ICIs). In 2017, the FDA approved two ICIs (pembrolizumab and nivolumab) for treatment of MSI-H/dMMR metastatic CRC (mCRC). In 2018, the CheckMate-142 trial demonstrated successful treatment of mCRC based on “double immunity” provided by nivolumab with ipilimumab, a regimen that may become a standard first-line treatment for MSI-H mCRC. In 2018, the FDA approved nivolumab alone or with ipilimumab for patients who progressed to MSI-H/dMMR mCRC after standard chemotherapy. The FDA then approved pembrolizumab alone as a first-line treatment for patients with MSI-H/dMMR CRC that was unresectable or metastatic. There is now interest in using these drugs in neoadjuvant immunotherapy (nIT) for patients with MSI-H/dMMR non-mCRC. In 2020, the NICHE trial marked the start of using nIT for CRC. This novel treatment of MSI-H/dMMR LACRC may change the approaches used for neoadjuvant therapy of other cancers. Our review of immunotherapy for CRC covers diagnosis and treatment, clinical prognostic characteristics, the mechanism of nIT, analysis of completed prospective and retrospective studies, and ongoing clinical trials, and the clinical practice of using nIT for MSI-H/dMMR LACRC. Our team also proposes a new organ-preservation strategy for patients with MSI-H/dMMR low LARC.

Immunotherapy in colorectal cancer: is the long-awaited revolution finally happening?

Immunotherapy has recently become a major treatment modality for several types of solid tumours, achieving remarkable and long-lasting remissions. In metastatic colorectal cancer patients (mCRC), immune checkpoint inhibitors (ICIs) were found to be effective as treatment for deficient mismatch repair (dMMR)/ microsatellite instability high (MSI-H) tumours and received regulatory approval for this indication. However, mCRC is a complex disease and dMMR/MSI-H tumours represent a minority of the cases; therefore, new strategies are needed to extend the benefits of immunotherapy to a larger population of patients. This review explores the immunological differences between dMMR/MSI-H and proficient mismatch repair (pMMR)/ microsatellite instability low (MSI-L) tumours, focuses on new proposed biomarkers to predict response to immunotherapy and illustrates results reported from the main clinical trials with immunotherapeutic agents in CRC, addressing the most promising approaches being currently developed.

Molecular and Dynamic Evaluation of Proteins Related to Resistance to Neoadjuvant Treatment with Chemoradiotherapy in Circulating Tumor Cells of Patients with Locally Advanced Rectal Cancer

The heterogeneity of response to neoadjuvant chemoradiotherapy (NCRT) is still a challenge in locally advanced rectal cancer (LARC). The evaluation of thymidylate synthase (TYMS) and RAD23 homolog B (RAD23B) expression in circulating tumor cells (CTCs) provides complementary clinical information. CTCs were prospectively evaluated in 166 blood samples (63 patients) with LARC undergoing NCRT. The primary objective was to verify if the absence of RAD23B/TYMS in CTCs would correlate with pathological complete response (pCR). Secondary objectives were to correlate CTC kinetics before (C1)/after NCRT (C2), in addition to the expression of transforming growth factor-β receptor I (TGF-βRI) with survival rates. CTCs were isolated by ISET and evaluated by immunocytochemistry (protein expression). At C1, RAD23B was detected in 54.1% of patients with no pCR and its absence in 91.7% of patients with pCR (p = 0.014); TYMS^- was observed in 90% of patients with pCR and TYMS⁺ in 51.7% without pCR (p = 0.057). Patients with CTC2 > CTC1 had worse disease-free survival (DFS) (p = 0.00025) and overall survival (OS) (p = 0.0036) compared with those with CTC2 ≤ CTC1. TGF-βRI expression in any time correlated with worse DFS (p = 0.059). To conclude, RAD23B/TYMS and CTC kinetics may facilitate the personalized treatment of LARC.