Phase II Trial of Ipilimumab with Stereotactic Radiation Therapy for Metastatic Disease: Outcomes, Toxicities, and Low-Dose Radiation-Related Abscopal Responses

Immunoradiotherapy for NSCLC: mechanisms, clinical outcomes, and future directions

Non-small-cell lung cancer (NSCLC) has an extremely low 5-year survival rate, with the only effective treatment being immunoradiotherapy (iRT). Here, we review the progress of clinical research on iRT for non-small-cell lung cancer (NSCLC) over 2018-2023, as well as the future directions. We first discuss the synergistic mechanisms of iRT, reflected in three aspects: immune regulation of RT, RT-activated immune-related pathways, and RT-related immune sensitization. iRT may include either external-beam or stereotactic-body RT combined with either immune checkpoint inhibitors (e.g., immunoglobulins against immune programmed cell death (PD) 1/PD ligand 1 or CD8+ T lymphocyte antigen 4) or traditional Chinese medicine drugs. Regarding clinical effectiveness and safety, iRT increases overall and progression-free survival and tumor control rate among patients with NSCLC but without a considerable increase in toxicity risk. We finally discuss iRT challenges and future directions reported over 2018-2023.

Harnessing the cGAS-STING pathway to potentiate radiation therapy: current approaches and future directions

In this review, we cover the current understanding of how radiation therapy, which uses ionizing radiation to kill cancer cells, mediates an anti-tumor immune response through the cGAS-STING pathway, and how STING agonists might potentiate this. We examine how cGAS-STING signaling mediates the release of inflammatory cytokines in response to nuclear and mitochondrial DNA entering the cytoplasm. The significance of this in the context of cancer is explored, such as in response to cell-damaging therapies and genomic instability. The contribution of the immune and non-immune cells in the tumor microenvironment is considered. This review also discusses the burgeoning understanding of STING signaling that is independent of inflammatory cytokine release and the various mechanisms by which cancer cells can evade STING signaling. We review the available data on how ionizing radiation stimulates cGAS-STING signaling as well as how STING agonists may potentiate the anti-tumor immune response induced by ionizing radiation. There is also discussion of how novel radiation modalities may affect cGAS-STING signaling. We conclude with a discussion of ongoing and planned clinical trials combining radiation therapy with STING agonists, and provide insights to consider when planning future clinical trials combining these treatments.

Low-dose radiation therapy mobilizes antitumor immunity: New findings and future perspectives

Radiotherapy has unique immunostimulatory and immunosuppressive effects. Although high-dose radiotherapy has been found to have systemic antitumor effects, clinically significant abscopal effects were uncommon on the basis of irradiating single lesion. Low-dose radiation therapy (LDRT) emerges as a novel approach to enhance the antitumor immune response due to its role as a leverage to reshape the tumor immune microenvironment (TIME). In this article, from bench to bedside, we reviewed the possible immunomodulatory role of LDRT on TIME and systemic tumor immune environment, and outlined preclinical evidence and clinical application. We also discussed the current challenges when LDRT is used as a combination therapy, including the optimal dose, fraction, frequency, and combination of drugs. The advantage of low toxicity makes LDRT potential to be applied in multiple lesions to amplify antitumor immune response in polymetastatic disease, and its intersection with other disciplines might also make it a direction for radiotherapy-combined modalities.

Immunotherapy and Radiotherapy Combinations for Sarcoma

Sarcomas are a heterogeneous group of bone and soft tissue tumors. Survival outcomes for advanced (unresectable or metastatic) disease remain poor, so therapeutic improvements are needed. Radiotherapy plays an integral role in the neoadjuvant and adjuvant treatment of localized disease as well as in the treatment of metastatic disease. Combining radiotherapy with immunotherapy to potentiate immunotherapy has been used in a variety of cancers other than sarcoma, and there is opportunity to further investigate combining immunotherapy with radiotherapy to try to improve outcomes in sarcoma. In this review, we describe the diversity of the tumor immune microenvironments for sarcomas and describe the immunomodulatory effects of radiotherapy. We discuss studies on the timing of radiotherapy relative to immunotherapy and studies on the radiotherapy dose and fractionation regimen to be used in combination with immunotherapy. We describe the impact of radiotherapy on the tumor immune microenvironment. We review completed and ongoing clinical trials combining radiotherapy with immunotherapy for sarcoma and propose future directions for studies combining immunotherapy with radiotherapy in the treatment of sarcoma.

Technical feasibility of novel immunostimulatory low-dose radiation for polymetastatic disease with CBCT-based online adaptive and conventional approaches

PURPOSE

A workflow/planning strategy delivering low-dose radiation therapy (LDRT) (1 Gy) to all polymetastatic diseases using conventional planning/delivery (Raystation/Halcyon = "conventional") and the AI-based Ethos online adaptive RT (oART) platform is developed/evaluated.

METHODS

Using retrospective data for ten polymetastatic non-small cell lung cancer patients (5-52 lesions each) with PET/CTs, gross tumor volumes (GTVs) were delineated using PET standardized-uptake-value (SUV) thresholding. A 1 cm uniform expansion of GTVs to account for setup/contour uncertainty and organ motion-generated planning target volumes (PTVs). Dose optimization/calculation used the diagnostic CT from PET/CT. Dosimetric objectives were: Dmin,0.03cc ≥ 95% (acceptable variation (Δ) ≥ 90%), V100% ≥ 95% (Δ ≥ 90%), and D0.03cc ≤ 120% (Δ ≤ 125%). Additionally, online adaptation was simulated. When available, subsequent diagnostic CT was used to represent on-treatment CBCT. Otherwise, the CT from PET/CT used for initial planning was deformed to simulate clinically representative changes.

RESULTS

All initial plans generated, both for Raystation and Ethos, achieved clinical goals within acceptable variation. For all patients, Dmin,0.03cc ≥ 95%, V100% ≥ 95%, and D0.03cc ≤ 120% goals were achieved for 84.8%/99.5%, 97.7%/98.7%, 97.4%/92.3%, in conventional/Ethos plans, respectively. The ratio of 50% isodose volume to PTV volume (R50% ), maximum dose at 2 cm from PTV (D2cm ), and the ratio of the 100% isodose volume to PTV volume (conformity index) in Raystation/Ethos plans were 7.9/5.9; 102.3%/88.44%; and 0.99/1.01, respectively. In Ethos, online adapted plans maintained PTV coverage whereas scheduled plans often resulted in geographic misses due to changes in tumor size, patient position, and body habitus. The average total duration of the oART workflow was 26:15 (min:sec) ranging from 6:43 to 57:30. The duration of each oART workflow step as a function of a number of targets showed a low correlation coefficient for influencer generation and editing (R2  = 0.04 and 0.02, respectively) and high correlation coefficient for target generation, target editing and plan generation (R2  = 0.68, 0.63 and 0.69, respectively).

CONCLUSIONS

This study demonstrates feasibility of conventional planning/treatment with Raystation/Halcyon and highlights efficiency gains when utilizing semi-automated planning/online-adaptive treatment with Ethos for immunostimulatory LDRT conformally delivered to all sites of polymetastatic disease.

The role of radiation therapy for de novo metastatic bladder and renal cancers

Metastatic bladder and renal cancers account respectively for 2.1% and 1.8% of cancer deaths worldwide. The advent of immune checkpoint inhibitors has revolutionized the management of metastatic disease, by demonstrating considerable improvements in overall survival. However, despite initial sensitivity to immune checkpoint inhibitors for most patients, both bladder and renal cancer are associated with short progression-free survival and overall survival, raising the need for further strategies to improve their efficacy. Combining systemic therapies with local approaches is a longstanding concept in urological oncology, in clinical settings including both oligometastatic and polymetastatic disease. Radiation therapy has been increasingly studied with either cytoreductive, consolidative, ablative or immune boosting purposes, but the long-term impact of this strategy remains unclear. This review intends to address the impact of radiation therapy with either curative or palliative intent, for synchronous de novo metastatic bladder and renal cancers.

Radiotherapy in the management of lung oligometastases

In recent years, the development of both medical imaging and new systemic agents (targeted therapy and immunotherapy) have revolutionized the field of oncology, leading to a new entity: oligometastatic disease. Adding local treatment of oligometastases to systemic treatment could lead to prolonged survival with no significant impact on quality of life. Given the high prevalence of lung oligometastases and the new systemic agents coming with increased pulmonary toxicity, this article provides a comprehensive review of the current state-of-art for radiotherapy of lung oligometastases. After reviewing pretreatment workup, the authors define several radiotherapy regimen based on the localization and size of the oligometastases. A comment on the synergistic combination of medical treatment and radiotherapy is also made, projecting on future steps in this specific clinical setting.

Opportunities and challenges in combining immunotherapy and radiotherapy in esophageal cancer

BACKGROUND

Immunotherapy has shown promise in the treatment of esophageal cancer, but using it alone only benefits a small number of patients. Most patients either do not have a significant response or develop secondary drug resistance. The combination of radiotherapy and immunotherapy appears to be a promising approach to treating esophageal cancer.

PURPOSE

We reviewed milestone clinical trials of radiotherapy combined with immunotherapy for esophageal cancer. We then discussed potential biomarkers for radiotherapy combined with immunotherapy, including programmed cell death-ligand 1 (PD-L1) status, tumor mutation burden (TMB), tumor-infiltrating lymphocytes, ct-DNA, imaging biomarkers, and clinical factors. Furthermore, we emphasize the key mechanisms of radiation therapy-induced immune stimulation and immune suppression in order to propose strategies for overcoming immune resistance in radiation therapy (RT). Lastly, we discussed the emerging role of low-dose radiotherapy (LDRT) , which has become a promising approach to overcome the limitations of high-dose radiotherapy.

CONCLUSION

Radiotherapy can be considered a triggering factor for systemic anti-tumor immune response and, with the assistance of immunotherapy, can serve as a systemic treatment option and potentially become the standard treatment for cancer patients.

Radiation dose, schedule, and novel systemic targets for radio-immunotherapy combinations

Immunotherapy combinations are being investigated to expand the benefit of immune checkpoint blockade across many cancer types. Radiation combinations, in particular using stereotactic body radiotherapy, are of keen interest because of underlying mechanistic rationale, safety, and availability as a standard of care in certain cancers. In addition to direct tumor cytotoxicity, radiation therapy has immunomodulatory effects such as induction of immunogenic cell death, enhancement of antigen presentation, and expansion of the T-cell receptor repertoire as well as recruitment and increased activity of tumor-specific effector CD8+ cells. Combinations of radiation with cytokines and/or chemokines and anti-programmed death 1 and anticytotoxic T-lymphocyte antigen 4 therapies have demonstrated safety and feasibility, as well as the potential to improve long-term outcomes and possibly induce out of irradiated field or abscopal responses. Novel immunoradiotherapy combinations represent a promising therapeutic approach to overcome radioresistance and further enhance systemic immunotherapy. Potential benefits include reversing CD8+ T-cell exhaustion, inhibiting myeloid-derived suppressor cells, and reversing M2 macrophage polarization as well as decreasing levels of colony-stimulating factor-1 and transforming growth factor-β. Here, we discuss current data and mechanistic rationale for combining novel immunotherapy agents with radiation therapy.

Concomitant Irradiation to Checkpoint Inhibitor Therapy of Hepatocellular Carcinoma Patients: A Systematic Retrospective, Single-Center Analysis

INTRODUCTION

Immunotherapy has been established as the standard treatment option for patients with advanced hepatocellular carcinoma (aHCC). Despite the increased efficacy, disease progression occurs in a relevant proportion of patients even after an objective response. Combination concepts with locoregional therapy are currently under investigation for hepatic disease but are also in discussion for the control of distant metastasis. Radiotherapy is a highly effective treatment modality for local tumor control. It is also thought to increase the efficacy of checkpoint inhibition and sensitize distant lesions to the effects of immunotherapy, but may potentially increase adverse effects. In our center, few patients with aHCC treated with immune checkpoint inhibitors (ICIs) received concomitant radiotherapy for symptom or disease control. The aim of this study was to retrospectively analyze adverse effects and efficacy of concomitant radiotherapy in patients with aHCC treated with checkpoint inhibition.

METHODS

To this aim, patients who received a combination of ICI and radiotherapy in our institution were retrospectively considered for analysis. The predefined inclusion criterion was radiotherapy after initiated checkpoint inhibition and continuation of ICI therapy for at least 8 weeks. Adverse effects and efficacy measurements were performed according to local standards.

RESULTS

The database search of 2016-2021 revealed six consecutive patients fulfilling the predefined criteria for concomitant ICI and radiotherapy. Three patients received high-dose-rate brachytherapy (15 Gy) to treat progredient hepatic lesions. Two patients received stereotactic body radiotherapy (SBRT) (25-30 Gy) for symptom control, and 1 patient received brachytherapy and SBRT to treat metastases. No severe adverse events were reported in the period (<6 months) after concomitant radiotherapy. In 5 out of 6 cases, long-term tumor control could be achieved by this therapeutic combination.

CONCLUSION

A good efficacy of concomitant radiotherapy and checkpoint inhibition has been achieved with no safety concerns. Further investigations should evaluate the safety, appropriate clinical context, and efficacy of this promising approach.

NLRP3 agonist enhances radiation-induced immune priming and promotes abscopal responses in anti-PD1 resistant model

Radiotherapy (XRT), a well-known activator of the inflammasome and immune priming, is in part capable of reversing resistance to anti-PD1 treatment. The NLRP3 inflammasome is a pattern recognition receptor which is activated by both exogenous and endogenous stimuli, leading to a downstream inflammatory response. Although NLRP3 is typically recognized for its role in exacerbating XRT-induced tissue damage, the NLRP3 inflammasome can also yield an effective antitumor response when used in proper dosing and sequencing with XRT. However, whether NLRP3 agonist boosts radiation-induced immune priming and promote abscopal responses in anti-PD1 resistant model is still unknown. Therefore, in this study, we paired intratumoral injection of an NLRP3 agonist with XRT to stimulate the immune system in both wild type (344SQ-P) and anti-PD1 resistant (344SQ-R) murine-implanted lung adenocarcinoma models. We found that the combination of XRT + NLPR3 agonist enhanced the control of implanted lung adenocarcinoma primary as well as secondary tumors in a radiological dose-dependent manner, in which 12Gyx3 fractions of stereotactic XRT was better than 5Gyx3, while 1Gyx2 did not improve the NLRP3 effect. Survival and tumor growth data also showed significant abscopal response with the triple therapy (12Gyx3 + NLRP3 agonist + α-PD1) in both 344SQ-P and 344SQ-R aggressively growing models. Multiple pro-inflammatory cytokines (IL-1b, IL-4, IL-12, IL-17, IFN-γ and GM-CSF) were elevated in the serum of mice treated with XRT + NLRP3 or triple therapy. The Nanostring results showed that NLRP3 agonist is capable of increasing antigen presentation, innate function, and T-cell priming. This study can be of particular importance to treat patients with immunologically-cold solid tumors whom are also refractory to prior checkpoint treatments.

The Role of Radiotherapy in the Management of Vaginal Melanoma: A Literature Review with a Focus on the Potential Synergistic Role of Immunotherapy

Among the mucosal melanomas, vaginal melanomas are very rare tumors, accounting for less than 20% of melanomas arising from the female genital tract. They occur most frequently in women in post-menopausal age, but younger patients may also experience this neoplasm, mainly located in the lower third of the vagina or the anterior wall. The optimal management of this tumor remains controversial, with surgery reported as the most frequently adopted approach. However, a clear benefit of surgical treatment in terms of survival has not yet been demonstrated. Conversely, radiotherapy may represent an attractive non-invasive alternative, and there are several favorable reports of the role of radiation therapy, either delivered with photons, brachytherapy, or hadrontherapy. A wide range of techniques and fractionation regimens are reported with substantially good tolerance to the treatment, and acute G3 or higher toxicities are reported only in the case of concurrent immunotherapy. Of note, due to the rarity of the disease, there is a lack of high-level evidence for the optimal therapeutic option. In this scenario, recent studies theorize the possibility of developing combinatorial approaches of radiotherapy with immunotherapy based on cutaneous melanomas reports. In this review, we aim to summarize the evidence available in the literature supporting the role of definitive radiotherapy for vaginal melanomas, with a focus on the combination of RT with immunotherapy, in terms of optimal timing and biological rationale.

Radiotherapy combined with immune checkpoint inhibitors in locally advanced/metastatic esophageal squamous cell carcinoma: clinical trials, efficacy and future directions

Esophageal squamous cell carcinoma (ESCC) is a common malignancy worldwide and often diagnosed at advanced stages with poor prognosis. Combination of radiotherapy and immunotherapy seems to be a promising approach for treating ESCC. This comprehensive review article summarizes the current state of combination of radiotherapy and immunotherapy in locally advanced/metastatic ESCC, delineates the clinical trials that merit attention, and outlines unresolved issues and future research directions in this field. The clinical trial findings suggest that radio-immunotherapy combination may improve tumor response and overall survival with manageable side effects, highlighting the importance of patient selection and the necessity for further research to optimize treatment strategies. Issues such as irradiation dosage, fractionation regimen, irradiation site and technique of radiotherapy, as well as the timing, sequence and duration of combination therapy will all affect treatment outcomes, justifying further in-depth investigation.

Radiation combined with immune checkpoint inhibitors for unresectable locally advanced non-small cell lung cancer: synergistic mechanisms, current state, challenges, and orientations

Until the advent of immune checkpoint inhibitors (ICIs), definitive radiotherapy (RT) concurrently with chemotherapy was recommended for unresectable, locally advanced non-small cell lung cancer (LA-NSCLC). The trimodality paradigm with consolidation ICIs following definitive concurrent chemoradiotherapy has been the standard of care since the PACIFIC trial. Preclinical evidence has demonstrated the role of RT in the cancer-immune cycle and the synergistic effect of RT combined with ICIs (iRT). However, RT exerts a double-edged effect on immunity and the combination strategy still could be optimized in many areas. In the context of LA-NSCLC, optimized RT modality, choice, timing, and duration of ICIs, care for oncogenic addicted tumors, patient selection, and novel combination strategies require further investigation. Targeting these blind spots, novel approaches are being investigated to cross the borders of PACIFIC. We discussed the development history of iRT and summarized the updated rationale for the synergistic effect. We then summarized the available research data on the efficacy and toxicity of iRT in LA-NSCLC for cross-trial comparisons to eliminate barriers. Progression during and after ICIs consolidation therapy has been regarded as a distinct resistance scenario from primary or secondary resistance to ICIs, the subsequent management of which has also been discussed. Finally, based on unmet needs, we probed into the challenges, strategies, and auspicious orientations to optimize iRT in LA-NSCLC. In this review, we focus on the underlying mechanisms and recent advances of iRT with an emphasis on future challenges and directions that warrant further investigation. Taken together, iRT is a proven and potential strategy in LA-NSCLC, with multiple promising approaches to further improve the efficacy. Video Abstract.

Tackling the current dilemma of immunotherapy in extensive-stage small cell lung cancer: A promising strategy of combining with radiotherapy

Progress in the treatment of small cell lung cancer (SCLC) has been modest over the past decades until the advent of immune checkpoint inhibitors, which have redefined the standard first-line treatment for extensive-stage SCLC (ES-SCLC). However, despite the positive results of several clinical trials, the limited survival benefit achieved suggests that the priming and sustaining of immunotherapeutic efficacy are poor and further investigation is urgently needed. In this review, we aim to summarize the potential mechanisms underlying the limited efficacy of immunotherapy and intrinsic resistance in ES-SCLC, including impaired antigen presentation and limited T cell infiltration. Moreover, to tackle the current dilemma, given the synergistic effects of radiotherapy on immunotherapy, especially the unique advantages of low-dose radiotherapy (LDRT), such as less immunosuppression and lower radiation toxicity, we propose radiotherapy as a booster to enhance the immunotherapeutic efficacy by overcoming the poor priming effect. Recent clinical trials, including ours, have also focused on adding radiotherapy, including LDRT, to first-line treatment of ES-SCLC. Additionally, we also suggest combination strategies to sustain the immunostimulatory effect of radiotherapy, as well as the cancer-immunity cycle, and further improve survival outcomes.

Opportunities and challenges of low-dose radiation to enable immunotherapy efficacy

Therapeutic monoclonal antibodies blocking different immune checkpoints, have demonstrated efficacy against a wide variety of solid tumors. The exclusion or absence of lymphocytes within the tumor microenvironment (TME) is one of the main resistance mechanisms to immune checkpoint inhibitor (ICI)-based therapies. Therefore, there is a growing interest in identifying novel approaches to promote T cell infiltration on immune-deserted (cold) and immune-excluded tumors to turn them into inflamed (hot) tumors. Here, we provide a comprehensive overview of the recently published studies showing the potential of low-dose radiation (LDRT) to reprogram the TME to allow and promote T-cell infiltration and thus, improve currently approved ICI-based therapies.

Implications of the Organ-Specific Immune Environment for Immune Priming Effect of Radiotherapy in Metastatic Setting

With the development of immune checkpoint inhibitors (ICIs), the tumour immune microenvironment (TIME) has been increasingly considered to improve cancer management. The TIME of metastatic lesions is strongly influenced by the underlying immune contexture of the organ in which they are located. The metastatic location itself appears to be an important prognostic factor in predicting outcomes after ICI treatment in cancer patients. Patients with liver metastases are less likely to respond to ICIs than patients with metastases in other organs, likely due to variations in the metastatic TIME. Combining additional treatment modalities is an option to overcome this resistance. Radiotherapy (RT) and ICIs have been investigated together as an option to treat various metastatic cancers. RT can induce a local and systemic immune reaction, which can promote the patient's response to ICIs. Here, we review the differential impact of the TIME according to metastatic location. We also explore how RT-induced TIME modifications could be modulated to improve outcomes of RT-ICI combinations.

The abscopal effect in patients with cancer receiving immunotherapy

Interest in the abscopal effect has been rekindled over the past decade with the advent of immunotherapy. Although purportedly elusive, this phenomenon is being increasingly reported. Venturing further using a multimodality approach with an array of systemic agents and unconventional modalities is direly needed. In this perspective, we describe the fundamentals of abscopal responses (ARs), explore combinations with systemic therapies that hold promise in eliciting ARs, and reconnoiter unconventional modalities that may induce ARs. Finally, we scrutinize prospective agents and modalities that exhibit preclinical ability to elicit ARs and discuss prognostic biomarkers, their limitations, and pathways of abscopal resistance for reproducibility.

Five-year overall survival with ipilimumab and stereotactic ablative radiotherapy for metastatic disease

PURPOSE

Ipilimumab plus stereotactic ablative radiotherapy (SABR) demonstrate satisfactory short-term clinical benefit and low toxicities in metastatic cancers. Here, we report the 5-year overall survival (OS) rates for patients with metastatic disease treated with this combined-modality therapy in a phase II trial (NCT02239900).

METHODS AND MATERIALS

SABR was delivered to patients with metastatic lesions in the liver and lung either during the first dose (concurrent) or 1 week after the second dose (sequential) of ipilimumab (every 3 weeks for 4 cycles). SABR was administered to liver or lung metastases as 50 Gy in 4 fractions or 60 Gy in 10 fractions, considering the tumor location. The OS rates at 12, 36, and 60 months were estimated by the Kaplan-Meier method; subgroup analyses of progression-free survival (PFS) and OS by SABR-targeted lesions (liver/lung) were performed by log-rank tests.

RESULTS

A total of 106 patients were enrolled in this long-term follow-up analysis. At the median follow-up time of 15.32 months (range, 0.97-82.13 months), the median PFS was 6.52 months (95% CI, 5.86-7.14) and the median OS was 15.32 months (95% CI,13.03-17.23). The 12-, 36-, and 60-month OS rates were 61%, 23%, and 15%, respectively. There was a significant difference in OS between cohorts (P = 0.039), with a stronger response observed in lung-treated subgroups. Patients who had received sequential fractions (50 Gy/4f) to the lung had improved OS compared to those who had received sequential fractions (18.29 vs 8.9 months, P = 0.043) to the liver. Subgroup analysis of SABR-targeted lesions showed that lung-targeted groups had significantly longer PFS (6.87 months vs. 5.63 months, P = 0.034) and OS (18.67 months vs. 13.63 months, P = 0.013) compared to liver-targeted groups. The sequence did not affect the outcomes of PFS and OS. Exploratory analyses showed that SABR-targeted lesions and smoking history comprised an independent risk factor for OS.

CONCLUSIONS

Updated 5-year OS data from the phase II trial demonstrate the long-term clinical benefit of ipilimumab and SABR, which warrants further research and cumulative data.

Metastases-directed stereotactic body radiotherapy in combination with targeted therapy or immunotherapy: systematic review and consensus recommendations by the EORTC-ESTRO OligoCare consortium

Stereotactic body radiotherapy (SBRT) for patients with metastatic cancer, especially when characterised by a low tumour burden (ie, oligometastatic disease), receiving targeted therapy or immunotherapy has become a frequently practised and guideline-supported treatment strategy. Despite the increasing use in routine clinical practice, there is little information on the safety of combining SBRT with modern targeted therapy or immunotherapy and a paucity of high-level evidence to guide clinical management. A systematic literature review was performed to identify the toxicity profiles of combined metastases-directed SBRT and targeted therapy or immunotherapy. These results served as the basis for an international Delphi consensus process among 28 interdisciplinary experts who are members of the European Society for Radiotherapy and Oncology (ESTRO) and European Organisation for Research and Treatment of Cancer (EORTC) OligoCare consortium. Consensus was sought about risk mitigation strategies of metastases-directed SBRT combined with targeted therapy or immunotherapy; a potential need for and length of interruption to targeted therapy or immunotherapy around SBRT delivery; and potential adaptations of radiation dose and fractionation. Results of this systematic review and consensus process compile the best available evidence for safe combination of metastases-directed SBRT and targeted therapy or immunotherapy for patients with metastatic or oligometastatic cancer and aim to guide today's clinical practice and the design of future clinical trials.

The RadScopal Technique as an Immune Adjuvant to Treat Cancer

Since the momentous discovery of X-rays, high-dose radiotherapy (H-XRT) has been a cornerstone for combating cancer. The high-energy electromagnetic waves induce direct damage to tumor-cells’ DNA, thereby halting cell growth and proliferation, and eventually leading to tumor eradication. Furthermore, recent evidence suggests that H-XRT may have immunomodulatory properties which arise from its ability to induce the release of neoantigens, which in turn prime T-cells and contribute to T-cell repertoire diversity. Throughout the years, there have been different treatment modalities introduced as complements to H-XRT that have yielded greater results than monotherapy alone. In this review, we will discuss preclinical and clinical data related to the recently introduced low-dose radiotherapy (L-XRT) modality. We will also explore the justification for combining L-XRT and H-XRT, which became known as the “RadScopal Technique”, as a novel immune adjuvant to treat cancer. In this analysis, we detail and dissect the physiological mechanisms of action of each modality and describe the synergistic amalgamation effect observed on primary and metastatic tumors. Finally, we will explore the impetus for further studies to investigate combinations of the “RadScopal Technique” with various immune-oncology drug candidates.

NLRP3 agonist enhances radiation-induced immune priming and promotes abscopal responses in anti-PD1 resistant model

Radiotherapy (XRT), a well-known activator of the inflammasome and immune priming, is in part capable of reversing resistance to anti-PD1 treatment. Although NLRP3 is typically observed for its role in exacerbating XRT-induced tissue damage, the NLRP3 inflammasome can also be protective and augment the effect of XRT when used in proper dosing and sequencing. However, whether NLRP3 agonist boosts radiation-induced immune priming and promote abscopal responses in anti-PD1 resistant model is still unknown. Therefore, in this study, we paired intratumoral injection of an NLRP3 agonist with XRT to stimulate the immune system in both wild type (344SQ-P) and anti-PD1 resistant (344SQ-R) murine-implanted lung adenocarcinoma models. We found that the combination of XRT + NLPR3 agonist enhanced control of implanted lung adenocarcinoma primary as well as secondary tumors in a radiological dose-dependent manner, in which 12Gy x 3 fractions of stereotactic XRT was better than 5Gy x 3, while 1Gy x 2 did not improve the NLRP3 effect. Survival and tumor growth data also showed significant abscopal response with the triple therapy (12Gyx3 + NLRP3 agonist + α-PD1) in both 344SQ-P and 344SQ-R aggressively growing models. Multiple pro-inflammatory cytokines (IL-1b, IL-4, IL-12, IL-17, IFN-γ and GM-CSF) were elevated in the serum of mice treated with XRT + NLRP3 or triple therapy. The Nanostring results showed that NLRP3 agonist is capable of increasing antigen presentation, innate function, and T-cell priming. This study can be of particular importance to treat patients with immunologically-cold solid tumors whom are also refractory to prior checkpoint treatments.

Application of individualized multimodal radiotherapy combined with immunotherapy in metastatic tumors

Radiotherapy is one of the mainstays of cancer treatment. More than half of cancer patients receive radiation therapy. In addition to the well-known direct tumoricidal effect, radiotherapy has immunomodulatory properties. When combined with immunotherapy, radiotherapy, especially high-dose radiotherapy (HDRT), exert superior systemic effects on distal and unirradiated tumors, which is called abscopal effect. However, these effects are not always effective for cancer patients. Therefore, many studies have focused on exploring the optimized radiotherapy regimens to further enhance the antitumor immunity of HDRT and reduce its immunosuppressive effect. Several studies have shown that low-dose radiotherapy (LDRT) can effectively reprogram the tumor microenvironment, thereby potentially overcoming the immunosuppressive stroma induced by HDRT. However, bridging the gap between preclinical commitment and effective clinical delivery is challenging. In this review, we summarized the existing studies supporting the combined use of HDRT and LDRT to synergistically enhance antitumor immunity, and provided ideas for the individualized clinical application of multimodal radiotherapy (HDRT+LDRT) combined with immunotherapy.

Immune checkpoint inhibitors and Carbon iON radiotherapy In solid Cancers with stable disease (ICONIC)

ICONIC is a multicenter, open-label, nonrandomized phase II clinical trial aiming to assess the feasibility and clinical activity of the addition of carbon ion radiotherapy to immune checkpoint inhibitors in cancer patients who have obtained disease stability with pembrolizumab administered as per standard-of-care. The primary end point is objective response rate, and the secondary end points are safety, survival and disease control rate. Translational research is an exploratory aim. The planned sample size is 27 patients. The study combination will be considered worth investigating if at least four objective responses are observed. If the null hypothesis is rejected, ICONIC will be the first proof of concept of the feasibility and clinical activity of the addition of carbon ion radiotherapy to immune checkpoint inhibitors in oncology.

The Current and Future Promises of Combination Radiation and Immunotherapy for Genitourinary Cancers

As the indications for the use of immunotherapy in genitourinary malignancies expand, its role in combination with standard or conventional therapies has become the subject of contemporary studies. Radiotherapy has multiple immunomodulating effects on anti-tumor immune response, which highlights potential synergistic role with immunotherapy agents. We sought to review the body of published data studying the combination of immunotherapy and radiotherapy as well as the rationale for combination therapy. Trial information and primary articles were obtained using the following terms "immunotherapy", "radiotherapy", "prostate cancer", and "bladder cancer." All articles and trials were screened to ensure they included combination radiotherapy and immunotherapy. The effects of radiation on the immune system, including both immunogenic and immunosuppressive effects, have been reported. There is a potential for combinatorial or synergistic effects between radiation therapy and immunotherapy in treating bladder and prostate cancers. However, results from ongoing and future clinical trials are needed to best integrate immunotherapy into current standard of care treatments for GU cancers.

Immunotherapy in Advanced NSCLC Without Driver Mutations: Available Therapeutic Alternatives After Progression and Future Treatment Options

The treatment paradigm of non-small-cell lung cancer without oncogenic drivers has varied dramatically in recent years and is constantly evolving. Immune- checkpoint inhibitors have demonstrated unprecedented durable efficacy in a subset of these patients, so these drugs have become the standard of care in most cases. There are different ways to deliver these agents, such as monotherapy and combinations of immunotherapy or chemotherapy plus immunotherapy. Treatment selection is complicated by an absence of head-to-head comparisons in randomized trials because these agents have gained approval by demonstrating superiority to platinum-doublet chemotherapy alone. Unfortunately, most patients will progress and die from their disease despite advances. Furthermore, after progression on these agents, there is a lack of randomized controlled data to support further management, constituting an unmet need. This review discusses the therapeutic alternatives after progression, summarizes mechanisms of resistance and progression patterns, and describes the main approaches under clinical investigation in the field.

On target methods to induce abscopal phenomenon for Off‐Target effects: From happenstance to happenings

Although the "abscopal phenomenon" has been described several decades ago, this phenomenon lately has been obtaining momentous traction with the dawn of immune-based therapies. There has been increased cross talk among radiation oncologists, oncologists and immunologists and consequently a surge in the number of prospective clinical trials. This must be coupled with translation work from these clinical trials to aid in eventual identification of patients who may benefit. Abscopal effects may be induced by local and systemic methods, conventional radiotherapy, particle radiation, radionucleotide methods, cryoablation and brachytherapy. These approaches have all been reported to be stimulate abscopal effect. Immune induction by immune checkpoint therapy, immune adjuvants, cellular therapy including CAR and NK cell therapies may generate systemic abscopal response. With increasing recognition of this effect, there remains a lot of work to explore the modalities of inducing abscopal responses and ultimate prediction or prognostication on stratifying who may benefit. Ultimately, there is an urgent need for prospective studies and data to tease apart which one of these modalities can be applied to the appropriate candidate, to the appropriate cancer at the appropriate setting. This review seeks to elucidate readers on the different modalities of radiation, systemic therapies and other techniques rarely explored to potentiate the abscopal effect from a mere coincidence to a finite occurrence.

Pulsed radiotherapy to mitigate high tumor burden and generate immune memory

Radiation therapy (XRT) has a well-established role in cancer treatment. Given the encouraging results on immunostimulatory effects, radiation has been increasingly used with immune-check-point inhibitors in metastatic disease, especially when immunotherapy fails due to tumor immune evasion. We hypothesized that using high-dose stereotactic radiation in cycles (pulses) would increase T-cell priming and repertoire with each pulse and build immune memory in an incremental manner. To prove this hypothesis, we studied the combination of anti-CTLA-4 and Pulsed radiation therapy in our 344SQ non-small cell lung adenocarcinoma murine model. Primary and secondary tumors were bilaterally implanted in 129Sv/Ev mice. In the Pulsed XRT group, both primary and secondary tumors received 12Gyx2 radiation one week apart, and blood was collected seven days afterwards for TCR repertoire analysis. As for the delayed-Pulse group, primary tumors received 12Gyx2, and after a window of two weeks, the secondary tumors received 12Gyx2. Blood was collected seven days after the second cycle of radiation. The immunotherapy backbone for both groups was anti-CTLA-4 antibody to help with priming. Treatment with Pulsed XRT + anti-CTLA-4 led to significantly improved survival and resulted in a delayed tumor growth, where we observed enhanced antitumor efficacy at primary tumor sites beyond XRT + anti-CTLA-4 treatment group. More importantly, Pulsed XRT treatment led to increased CD4⁺ effector memory compared to single-cycle XRT. Pulsed XRT demonstrated superior efficacy to XRT in driving antitumor effects that were largely dependent on CD4⁺ T cells and partially dependent on CD8⁺ T cells. These results suggest that combinatorial strategies targeting multiple points of tumor immune evasion may lead to a robust and sustained antitumor response.

Pathological complete response in MMR-deficient/MSI-high and KRAS-mutant patient with locally advanced rectal cancer after neoadjuvant chemoradiation with immunotherapy: A case report

To date, preoperative chemoradiation (CRT) is the standard of care for patients with locally advanced rectal cancer (LARC) regardless of status of mismatch repair. Immunotherapy showed promising results in the neoadjuvant treatment trials in patients with mismatch repair-deficient (dMMR) or high microsatellite instability (MSI-H) LARC. The efficacy of CRT plus programmed death 1 (PD-1) inhibitor in these patients with complex gene mutation remains unclear. Additionally, very few studies reported on whether such combination could induce abscopal effect. We report a case of dMMR and MSI-H LARC with KRAS mutation that achieved pathological complete response of primary lesion and liver metastases after neoadjuvant short-course radiotherapy followed by four cycles chemotherapy of XELOX plus PD-1 inhibitor tislelizumab and a subsequent total mesorectal excision. This case indicates that this combined treatment strategy has remarkable clinical response both in locoregional and distant diseases, which potentially leads to reduction in the risk of distant metastases and better locoregional control for this subgroup of population.

Radioimmunotherapy in HPV-Associated Head and Neck Squamous Cell Carcinoma

HPV-associated head and neck squamous cell carcinoma (HNSCC) is a cancer entity with unique biological and clinical characteristics that requires more personalized treatment strategies. As the backbone of conventional therapeutics, radiation is now harnessed to synergize with immunotherapy in multiple malignancies. Accumulating preclinical and clinical data have suggested the potential of radioimmunotherapy in eliciting local and systemic anti-tumor response via direct killing of tumor cells and immunogenic cell death. However, this effect remains uncertain in HPV-associated HNSCC. Owing to its intrinsic radiosensitivity and distinct tumor microenvironment, HPV-associated HNSCC may represent a good candidate for radioimmunotherapy. In this review, we provide a detailed illustration of the biology, the genomic features, and immune landscapes of HPV-associated HNSCC that support the synergism between radiation and immune agents. The interaction between radiotherapy and immunotherapy is described. We also highlight the present evidence as well as ongoing trials using different combination strategies in the recurrent/metastatic or definitive settings. In addition, we have summarized the challenges and outlook for future trial design, with special emphasis on radiotherapy optimization and novel therapeutic options to incorporate.

Radiotherapy combined with immunotherapy: the dawn of cancer treatment

Radiotherapy (RT) is delivered for purposes of local control, but can also exert systemic effect on remote and non-irradiated tumor deposits, which is called abscopal effect. The view of RT as a simple local treatment has dramatically changed in recent years, and it is now widely accepted that RT can provoke a systemic immune response which gives a strong rationale for the combination of RT and immunotherapy (iRT). Nevertheless, several points remain to be addressed such as the interaction of RT and immune system, the identification of the best schedules for combination with immunotherapy (IO), the expansion of abscopal effect and the mechanism to amplify iRT. To answer these crucial questions, we roundly summarize underlying rationale showing the whole immune landscape in RT and clinical trials to attempt to identify the best schedules of iRT. In consideration of the rarity of abscopal effect, we propose that the occurrence of abscopal effect induced by radiation can be promoted to 100% in view of molecular and genetic level. Furthermore, the “radscopal effect” which refers to using low-dose radiation to reprogram the tumor microenvironment may amplify the occurrence of abscopal effect and overcome the resistance of iRT. Taken together, RT could be regarded as a trigger of systemic antitumor immune response, and with the help of IO can be used as a radical and systemic treatment and be added into current standard regimen of patients with metastatic cancer.

A ‘Hybrid’ Radiotherapy Regimen Designed for Immunomodulation: Combining High-Dose Radiotherapy with Low-Dose Radiotherapy

Simple Summary

Radiotherapy is an important cancer treatment. Aside from its direct killing effect, it also affects anti-tumor immunity. However, radiotherapy’s immune effect is not clear; it depends on the dose and fraction, cancer type, combined immunotherapy, and many other factors. Studies have focused on the optimal radiotherapy regimen to stimulate anti-tumor immunity, but conflicts exist, especially regarding the best radiation dose and fractions. Interestingly, high-dose radiotherapy and low-dose radiotherapy have complementary effects on stimulating anti-tumor immunity. Preclinical studies supporting this finding have accumulated, but gaps between theory and clinical practice still exist. This review summarizes the evidence supporting the use of this ‘hybrid’ radiotherapy approach to effectively stimulate anti-tumor immunity, explains the immune mechanisms of this combination, raises questions that must be addressed in clinical practice, and provides ideas for designing individualized treatment to increase efficiency in stimulating anti-tumor immunity using high-dose plus low-dose radiotherapy.

Abstract

Radiotherapy (RT) affects anti-tumor immunity. However, the exact impact of RT on anti-tumor immune response differs among cancer types, RT dose and fractions, patients’ innate immunity, and many other factors. There are conflicting findings on the optimal radiation dose and fractions to stimulate effective anti-tumor immunity. High-dose radiotherapy (HDRT) acts in the same way as a double-edged sword in stimulating anti-tumor immunity, while low-dose radiotherapy (LDRT) seems to play a vital role in modulating the tumor immune microenvironment. Recent preclinical data suggest that a ‘hybrid’ radiotherapy regimen, which refers to combining HDRT with LDRT, can reap the advantages of both. Clinical data have also indicated a promising potential. However, there are still questions to be addressed in order to put this novel combination therapy into clinical practice. For example, the selection of treatment site, treatment volume, the sequencing of high-dose radiotherapy and low-dose radiotherapy, combined immunotherapy, and so on. This review summarizes the current evidence supporting the use of HDRT + LDRT, explains possible immune biology mechanisms of this ‘hybrid’ radiotherapy, raises questions to be considered when working out individualized treatment plans, and lists possible avenues to increase efficiency in stimulating anti-tumor immunity using high-dose plus low-dose radiotherapy.

Abscopal effect of radiation therapy and nivolumab in a patient with combined small-cell lung cancer: a case report

The paradigm for combined small-cell lung carcinoma (C-SCLC) is according to standard SCLC treatment with poor outcomes. The efficacy of immune checkpoint inhibitor (ICI) monotherapy for pretreated SCLC is still limited. Clinical researches exploring radiotherapy combined with immunotherapy showed promising synergistic effects in several tumors. We report one C-SCLC case after resistant to comprehensive treatment receiving nivolumab combined with radiotherapy achieving clinical complete remission (CCR). The combination module of ICI and radiation could be an option for relapsed C-SCLC, and the prognostic indicators need further research.

Safety and Tolerability of Metastasis Directed Radiotherapy in the Era of Evolving Systemic, Immune and Targeted Therapies

AbstractPurpose

Systemic, immune, and target therapies are growing in use in the management of metastatic cancers. The aim of this review was to describe up-to-date published data on the safety and tolerability of metastasis-directed hypofractionated radiation therapy (RT) when combined with newer systemic, immune, and targeted therapies and to provide suggested strategies to mitigate potential toxicities in the clinical setting.

Methods and Materials

A comprehensive search was performed for the time period between 1946 and August 2021 using predetermined keywords describing the use of noncentral nervous system palliative RT with commonly used targeted systemic therapies on PubMed and Medline databases. A total of 1022 articles were screened, and 130 met prespecified criteria to be included in this review.

Results

BRAF and MEK inhibitors are reported to be toxic when given concurrently with RT; suspension 3 days and 1 to 2 days, respectively, prior and post-RT is suggested. Cetuximab, erlotinib/gefitinib, and osimertinib were generally safe to use concomitantly with conventional radiation. But in a palliative/hypofractionated RT setting, suspending cetuximab during radiation week, erlotinib/gefitinib 1 to 2 days, and osimertinib ≥2 days pre- and post-RT is suggested. Vascular endothelial growth factor inhibitors such as bevacizumab reported substantial toxicities, and the suggestion is to suspend 4 weeks before and after radiation. Less data exist on sorafenib and sunitinib; 5 to 10 days suspension before and after RT should be considered. As a precaution, until further data are available, for cyclin-dependent kinase 4-6 inhibitors, consideration of suspending treatment 1 to 2 days before and after RT should be given. Ipilimumab should be suspended 2 days before and after RT, and insufficient data exist for other immunotherapy agents. Trastuzumab and pertuzumab are generally safe to use in combination with RT, but insufficient data exist for other HER2 target therapy.

Conclusions

Suggested approaches are described, using up-to-date literature, to aid clinicians in navigating the integration of newer targeted agents with hypofractionated palliative and/or ablative metastatic RT. Further prospective studies are required.

Low-dose irradiation for reversing immunotherapy resistance: how to translate?

The use of low-dose irradiation (LDI) for mobilizing innate and adaptive immunity is gaining interest among the scientific community. Recent evidence suggests that LDI can reprogramme the tumor microenvironment, induce inflammation and turn cold tumors susceptible to immunecheckpoint blockade therapy. Translating immuno-radiation preclinical findings in the clinic is more challenging than expected. We propose therapeutic strategies for combining LDI with immunotherapy, and emphasize the importance of pursuing clinical research to determine optimal radiation dosage, fractionation, volumes, and sequencing to stimulate immune-mediated tumor responses.

Clinicopathological features and programmed death-ligand 1 immunohistochemical expression in a multicenter cohort of uterine and ovarian melanomas: a retrospective study in Japan (KCOG-G1701s)

The objective of this study was to propose prognostic factors and optimal treatment strategies by analyzing the clinicopathological features and programmed death-ligand 1 (PD-L1) expression. We analyzed 31 patients diagnosed with uterine or ovarian melanoma between 1997 and 2017 in the Kansai Clinical Oncology Group/Intergroup. Twenty-four and seven patients with cervical and ovarian melanomas were included, respectively. Immune checkpoint inhibitors were used in seven patients, and the objective response rate was 40%. Notably, two patients with objective responses had a high PD-L1 expression. Ten and four patients with cervical and ovarian melanomas, respectively, had high PD-L1 immunohistochemical expressions. Multivariate analysis revealed that tumor stage was an independent prognostic factor for progression-free survival in patients with cervical melanomas. In patients with ovarian melanomas, the 1-year cumulative progression-free and overall survival rates were 0 and 29%, respectively. Kaplan-Meier analyses revealed that age <60 years was associated with poorer progression-free and overall survivals in patients with ovarian melanomas. In patients with cervical melanomas, the 1-, 3-, and 5-year cumulative overall survival rates were 53, 32, and 16%, respectively. Histological atypia was associated with a poorer progression-free survival, but there was no difference in survival between patients who underwent radical hysterectomy and those who did not. The present study is a large cohort study of uterine and ovarian melanomas, which are aggressive tumors with a significantly poor prognosis, even after standard surgery and adjuvant therapy. The use of immune checkpoint inhibitors is a promising and effective treatment option.

Optimize Local Therapy for Oligometastatic and Oligoprogressive Non-Small Cell Lung Cancer to Enhance Survival

Metastatic non-small cell lung cancer (NSCLC) is highly heterogeneous, and there are patients with limited areas of metastases (oligometastases) or progression (oligoprogression) whose natural history and prognosis can be considerably more favorable. As a result, local therapy may offer these patients a chance at clinically meaningful disease control and/or cure. This review begins by describing the current status of the existing prospective data, including evidence of overall survival improvements from multiple randomized trials. Given the nascence of this realm, the review then examines ongoing controversies and unresolved issues regarding local therapy for oligometastatic and oligoprogression. First, the role of local therapy in the setting of targeted therapies and immunotherapy is discussed, because most published randomized trials of local therapy have been performed in the context of chemotherapy, which is no longer the standard of care for most patients with metastatic NSCLC. Refining patient selection for local therapy is then reviewed, including clinical factors (such as control of the primary and regional lymph node sites, the heterogeneous definitions of oligometastases/oligoprogression, and the underrepresentation of brain metastases in existing randomized data) and novel pathologic/molecular biomarkers. Next, because there also remains no consensus regarding the optimal modality of local therapy, the advantages and disadvantages of stereotactic radiotherapy, surgery, and other ablative techniques are discussed. Subsequently, methods to optimize radiotherapy are examined, including controversies regarding the optimal dose/fractionation and timing/sequencing scheme. A discussion regarding potentially extending the existing data to polymetastatic NSCLC follows. The review concludes with remarks regarding prudently designing randomized trials of local therapy going forward, including the benefits and drawbacks of specific endpoints meriting further testing in this unique population.

Outcomes of SBRT for lung oligo-recurrence of non-small cell lung cancer: a retrospective analysis

The benefit of local ablative therapy (LAT) for oligo-recurrence has been investigated and integrated into the treatment framework. In recent decades, stereotactic body radiation therapy (SBRT) has been increasingly used to eliminate metastasis owing to its high rate of local control and low toxicity. This study aimed to investigate the outcomes of SBRT for patients with lung oligo-recurrence of non-small cell lung cancer (NSCLC) from our therapeutic center. Patients with lung oligo-recurrence of NSCLC treated with SBRT between December 2011 and October 2018 at Cancer Hospital of the University of Chinese Academy of Sciences (Zhejiang Cancer Hospital) were reviewed. The characteristics, treatment-related outcomes, and toxicities of the patients were analyzed. Univariable and multivariable Cox regression were performed to identify the factors associated with survival. A total of 50 patients with lung oligo-recurrence of NSCLC were enrolled. The median follow-up period was 23.6 months. The 3-year local progression-free survival (LPFS), progression-free survival (PFS) and overall survival (OS) after SBRT were 80.2%, 21.9% and 45.3%, respectively. Patients in the subgroup with LAT to all residual diseases showed significantly improved OS and PFS. No treatment-related death occurred after SBRT. SBRT is a feasible option to treat patients with lung oligo-recurrence of NSCLC, with high rates of local control and low toxicity. LAT to all residual diseases was associated with better survival outcomes. Future prospective randomized clinical trials should evaluate SBRT strategies for such patients.

Novel Use of Low-Dose Radiotherapy to Modulate the Tumor Microenvironment of Liver Metastases

Despite multiple therapeutic approaches, the presence of liver metastases carries a guarded prognosis, urgently necessitating further clinical and scientific research to develop curative interventions. The liver is an immunoprivileged organ that suppresses the effectiveness of immunotherapies in patients with hepatic metastases. Cancer immunotherapies have been successfully bolstered by low-dose radiotherapy (LDRT), which is capable of reprogramming the tumor microenvironment (TME) from an immunosuppressive to an immunostimulatory one. Likewise, LDRT may be able to revoke the immune privilege enjoyed by the liver, permitting successful immunotherapies there. Here, we first review challenges that face the treatment of liver metastases. We next outline emerging preclinical and clinical evidence supporting enhanced systemic tumor control of LDRT in the context of cancer immunotherapy. Finally, we will discuss the rationale of combining liver-directed LDRT with immunostimulatory strategies to overcome immune resistance and achieve better clinical response. This notion is supported by a recent case study in which a patient who had progressed following T cell therapy experienced a complete response after LDRT to the liver.

Tissue-specific Tregs in cancer metastasis: opportunities for precision immunotherapy

Decades of advancements in immuno-oncology have enabled the development of current immunotherapies, which provide long-term treatment responses in certain metastatic cancer patients. However, cures remain infrequent, and most patients ultimately succumb to treatment-refractory metastatic disease. Recent insights suggest that tumors at certain organ sites exhibit distinctive response patterns to immunotherapy and can even reduce antitumor immunity within anatomically distant tumors, suggesting the activation of tissue-specific immune tolerogenic mechanisms in some cases of therapy resistance. Specialized immune cells known as regulatory T cells (Tregs) are present within all tissues in the body and coordinate the suppression of excessive immune activation to curb autoimmunity and maintain immune homeostasis. Despite the high volume of research on Tregs, the findings have failed to reconcile tissue-specific Treg functions in organs, such as tolerance, tissue repair, and regeneration, with their suppression of local and systemic tumor immunity in the context of immunotherapy resistance. To improve the understanding of how the tissue-specific functions of Tregs impact cancer immunotherapy, we review the specialized role of Tregs in clinically common and challenging organ sites of cancer metastasis, highlight research that describes Treg impacts on tissue-specific and systemic immune regulation in the context of immunotherapy, and summarize ongoing work reporting clinically feasible strategies that combine the specific targeting of Tregs with systemic cancer immunotherapy. Improved knowledge of Tregs in the framework of their tissue-specific biology and clinical sites of organ metastasis will enable more precise targeting of immunotherapy and have profound implications for treating patients with metastatic cancer.

Which treatment after first line therapy in NSCLC patients without genetic alterations in the era of immunotherapy?

Cancer immunotherapy has produced an unprecedented durable response rate, thus shifting from traditional doublet chemotherapy to immunotherapy-based treatments with and without chemotherapy as the first line strategies for advanced non-small cell lung cancer patients without a molecular driver. However, the majority of patients do not benefit from the treatment or may relapse after a period of response. As few treatment options are available after failure of cancer immunotherapy, including the combination of chemotherapy and anti-angiogenic drugs, a better understanding of the mechanisms limiting cancer immunotherapy may be of help in the definition of the best second line. Whereas only retrospective data support an immunotherapy rechallenge approach, new combination strategies including immunotherapy and cell-signaling inhibitors or double immunotherapy represent the newest and most promising strategy to overcome primary or acquired resistance to first line immunotherapy.

Radiotherapy driven immunomodulation of the tumor microenvironment and its impact on clinical outcomes: a promising new treatment paradigm

Traditional treatment approaches for advanced malignancies have been associated with limited clinical outcomes necessitating the development of novel therapies. However, the ability of radiotherapy to induce pro-immunogenic changes in tumor immune microenvironment can be leveraged when combined with systemic agents. Radio-immunotherapeutic initiatives employing the use of monoclonal antibodies, genetically engineered T cells, cytokines and virus-vector mediated gene therapies have demonstrated promising potential for the management of various solid malignancies. Future studies incorporating biomarker enrichment strategies and radiobiological variables could pave the way for immune-oncology based personalized medicine approaches to be integrated in standard of care practices for the treatment of challenging clinical populations.

Immune Checkpoints Inhibitors and SRS/SBRT Synergy in Metastatic Non-Small-Cell Lung Cancer and Melanoma: A Systematic Review

Background: Several immunotherapy (IT) agents are FDA approved for treatment of melanoma and non-small-cell lung cancer (NSCLC). The addition of stereotactic radiosurgery (SRS) or stereotactic body radiation therapy (SBRT) to immunotherapy looks promising. A systematic review was conducted to evaluate the possible synergistic effects of immune checkpoints inhibitors (ICIs) and stereotactic radiation therapy in melanoma and NSCLC. Materials and methods: Pubmed databases from January 2010 to December 2020 were reviewed to identify English language studies reporting control of local and abscopal effect of the combination of ICI-SBRT/SRS in metastatic NSCLC and melanoma cancer. The inclusion criteria were followed according to PICO criteria. Results: Thirty-nine articles were included of the 2141 initial results. The reported rates for local control were 16.5–100% and 40–94% in brain and extracerebral metastases, respectively. Distant/abscopal response rates were 1–45% in extracerebral metastases. Abscopal effect could not be evaluated in brain metastases because it was not reported in studies. Treatments were well tolerated with few grade 4 toxicities and no grade 5. Conclusions: The combined treatment of ICI-SBRT/SRS achieves high local control and non-negligible abscopal response in patients with extracerebral metastases, with its benefit in cerebral metastases being more controversial. Clinical trials are needed to better characterize the potential synergism.

Combined treatment of non-small cell lung cancer using radiotherapy and immunotherapy: challenges and updates

The efficacy of immunotherapy for advanced non‐small cell lung cancer (NSCLC) remains unsatisfactory, as the majority of patients either do not experience an objective response or acquire secondary resistance. As a result, several methods to enhance the systemic efficacy of immunotherapy have been investigated, including a large area of active research by combining immunotherapy with radiation therapy (RT). Given the rapidly burgeoning concept of combining immunotherapy and RT for increasing therapeutic benefit, we review the progress in this field thus far and explore further avenues for enhancing this combination. This review commences with a discussion of the only two existing randomized trials (and a pooled analysis) showing that the addition of RT to immunotherapy improves the abscopal response rate, progression‐free survival, and overall survival in metastatic NSCLC patients. We then discussed factors and biomarkers that may be associated with a proportionally greater benefit to additional RT, such as low programmed cell death protein ligand 1 (PD‐L1) status, tumor mutational burden (TMB), and patient's immune function. Next, the implementation of RT to overcome immunotherapy resistance is discussed, including a mechanistic discussion and methods with which these mechanisms could be exploited. Lastly, the emerging role of low‐dose RT is discussed, which may help to overcome inhibitory signals in the tumor stroma that limit T‐cell infiltration. Taken together, given the current state of this rapidly expanding realm, these futuristic strategies may be reflected upon to further enhance the efficacy of immunotherapy for a wider group of patients.

The Abscopal Effect: A Review of Pre-Clinical and Clinical Advances

Radiotherapy has been used for more than a hundred years to cure or locally control tumors. Regression of tumors outside of the irradiated field was occasionally observed and is known as the abscopal effect. However, the occurrence of systemic anti-tumor effects was deemed too rare and unpredictable to be a therapeutic goal. Recent studies suggest that immunotherapy and radiation in combination may enhance the abscopal response. Increasing numbers of cases are being reported since the routine implementation of immune checkpoint inhibitors, showing that combined radiotherapy with immunotherapy has a synergistic effect on both local and distant (i.e., unirradiated) tumors. In this review, we summarize pre-clinical and clinical reports, with a specific focus on the mechanisms behind the immunostimulatory effects of radiation and how this is enhanced by immunotherapy.

The Combination of Radiotherapy With Immunotherapy and Potential Predictive Biomarkers for Treatment of Non-Small Cell Lung Cancer Patients

Radiotherapy is an effective local treatment modality of NSCLC. Its capabilities of eliminating tumor cells by inducing double strand DNA (dsDNA) damage and modulating anti-tumor immune response in irradiated and nonirradiated sites have been elucidated. The novel ICIs therapy has brought hope to patients resistant to traditional treatment methods, including radiotherapy. The integration of radiotherapy with immunotherapy has shown improved efficacy to control tumor progression and prolong survival in NSCLC. In this context, biomarkers that help choose the most effective treatment modality for individuals and avoid unnecessary toxicities caused by ineffective treatment are urgently needed. This article summarized the effects of radiation in the tumor immune microenvironment and the mechanisms involved. Outcomes of multiple clinical trials investigating immuno-radiotherapy were also discussed here. Furthermore, we outlined the emerging biomarkers for the efficacy of PD-1/PD-L1 blockades and radiation therapy and discussed their predictive value in NSCLC.

American Radium Society Appropriate Use Criteria for Radiation Therapy in Oligometastatic or Oligoprogressive Non-Small Cell Lung Cancer

PURPOSE

Recent randomized studies have suggested improvements in progression-free and overall survival with the addition of stereotactic body radiation therapy (SBRT, also known as SABR) in patients with oligometastatic non-small cell lung cancer. Given the novelty and complexity of incorporating SBRT in the oligometastatic setting, the multidisciplinary American Radium Society Lung Cancer Panel was assigned to create appropriate use criteria on SBRT as part of consolidative local therapy for patients with oligometastatic and oligoprogressive non-small cell lung cancer.

METHODS AND MATERIALS

A review of the current literature was conducted from January 1, 2008, to December 25, 2020, using the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines to systematically search the PubMed database to retrieve a comprehensive set of relevant articles.

RESULTS

Based on representation in existing randomized trials, the panel defined the term "oligometastasis" as ≤3 metastatic deposits (not including the primary tumor) in the previously untreated setting or after first-line systemic therapy after the initial diagnosis. "Oligoprogression" also referred to ≤3 discrete areas of progression in the setting of prior or ongoing receipt of systemic therapy. In all appropriate patients, the panel strongly recommends enrollment in a clinical trial whenever available. For oligometastatic disease, administering first-line systemic therapy followed by consolidative radiation therapy (to all sites plus the primary/nodal disease) is preferred over up-front radiation therapy. Owing to a dearth of data, the panel recommended that consolidative radiation therapy be considered on a case-by-case basis for 4 to 5 sites of oligometastatic disease, driver mutation-positive oligometastatic disease without progression on up-front targeted therapy, and oligoprogressive cases.

CONCLUSIONS

Although SBRT/SABR appears to be both safe and effective in treating patients with limited metastatic sites of disease, many clinical circumstances require individualized management and strong multidisciplinary discussion on account of the limited existing data.

Pulsed Radiation Therapy to Improve Systemic Control of Metastatic Cancer

Radiation therapy (RT) is emerging as an interventional modality in the cancer-immunity cycle, augmenting the activation of an adaptive immune response against tumors. RT, particularly in combination with immunotherapy, can enhance immune memory effects and shape the tumor-directed T-cell populations. However, a single cycle of RT delivered to a limited number of polymetastatic lesions is rarely sufficient to achieve systemic control. We hypothesize that several rounds of RT, akin to several rounds of immunotherapeutic drugs, is likely to provide greater clinical benefit to patients with metastatic disease. We propose that the repeated exposure to tumor antigens released by “pulsed-RT” (i.e., treating 2-4 tumor lesions with 3 irradiation cycles given one month apart) may amplify the adaptive immune response by expanding the tumor-specific T-cell receptor repertoire, the production of high-affinity tumor antibodies, and the generation of memory lymphocytes and thereby improve immune control of systemic disease.