The Abscopal Effect of Stereotactic Radiotherapy and Immunotherapy: Fool's Gold or El Dorado?

Non-targeted effects of radiation therapy for glioblastoma

Radiotherapy is recommended for the treatment of brain tumors such as glioblastoma (GBM) and brain metastases. Various curative and palliative scenarios suggest improved local-regional control. Although the underlying mechanisms are not yet clear, additional therapeutic effects have been described, including proximity and abscopal reactions at the treatment site. Clinical and preclinical data suggest that the immune system plays an essential role in regulating the non-targeted effects of radiotherapy for GBM. This article reviews current biological mechanisms for regulating the non-targeted effects caused by external and internal radiotherapy, and how they might be applied in a clinical context. Optimization of therapeutic regimens requires assessment of the complexity of the host immune system on the activity of immunosuppressive or immunostimulatory cells, such as glioma-associated macrophages and microglia. This article also discusses recent preclinical models adapted to post-radiotherapy responses. This narrative review explores and discusses the current status of immune responses both locally via the "bystander effect" and remotely via the "abscopal effect". Preclinical and clinical observations demonstrate that unirradiated cells, near or far from the irradiation site, can control the tumor response. Nevertheless, previous studies do not address the problem in its global context, and present gaps regarding the link between the role of the immune system in the control of non-targeted effects for different types of radiotherapy and different fractionation schemes applied to GBM. This narrative synthesis of the scientific literature should help to update and critique available preclinical and medical knowledge. Indirectly, it will help formulate new research projects based on the synthesis and interpretation of results from a non-systematic selection of published studies.

Clinical outcomes and timing on the combination of focal radiation therapy and immunotherapy for the treatment of brain metastases

Introduction

Radiotherapy is one of the standard treatments for brain metastases (BM). Over the past years, the introduction of immunotherapy as routine treatment for solid tumors has forced investigators to review and evaluate how it would interact with radiation. Radiation and Immunotherapy have shown a synergic effect activating the host's immune system and enhancing treatment response. The combinatory effect on BM is currently under investigation.

Methods

Data published on Pubmed to determine toxicity, survival, treatment characteristics and timing on the combination of radiotherapy and immunotherapy for the treatment of BM has been reviewed.

Results

Mostly retrospective reviews report an improvement of intracranial progression free survival (iPFS) when combining radioimmunotherapy for BM patients. Two systematic reviews and meta-analysis and one phase II prospective trial also report a benefit on iPFS without an increase of toxicity. Among the published literature, the definition of concurrency is heterogeneous, being one month or even narrowed intervals correlated to better clinical outcomes. Toxicity due to concurrent radioimmunotherapy, specifically symptomatic radionecrosis, is also directly analyzed and reported to be low, similar to the toxicity rates secondary to stereotactic radiosurgery alone.

Conclusion

Radiation combined with immunotherapy has shown in predominantly retrospective reviews a synergic effect on the treatment of BM. The concurrent combination of radioimmunotherapy is a feasible therapeutic strategy and seems to improve clinical outcomes, especially iPFS, when delivered within <30 days. Larger prospective and randomized studies are needed to establish reliable outcomes, best delivery strategies and toxicity profile.

Local treatment in oligometastasis from breast cancer: an overview

Oligometastasic breast cancer (OMBC) consists of breast cancer patient with a limited number of systemic metastases (≤ 5), all of them candidates for local ablative treatment with the intention of achieving long-term control of the metastasis and, eventually, an increase in survival The first consensus for the management of patients with oligometastatic breast cancer (OMBC) was published in 2007, establishing that a more aggressive multidisciplinary strategy is recommended in order to increase the survival while maintaining a good quality of life. The current scientific evidence is based on observational studies, mainly retrospective, systematic reviews and meta-analyses, and only a randomized nonexclusive study of oligometastatic (OM) published. All trials with Stereotactic Body Radiation Therapy (SBRT) in OM cancer have shown excellent tolerance and good local control, although first trials on Lung SBRT did not prove so excellent tolerance and had some deaths due to bronchus irradiation and secondary hemoptysis. There are multiple ongoing studies researching the benefit of SBRT in oligometastatic breast cancer. Despite the lack of impact on survival seen in the NRG BR-002 Trial, SBRT probably allows the delay of the systemic treatment until progression, and so, improves the quality of life of patients. We have to wait for the results of the ongoing and future studies for clarification of the role of local treatment in OMBC.

Trial watch: chemotherapy-induced immunogenic cell death in oncology

Immunogenic cell death (ICD) refers to an immunologically distinct process of regulated cell death that activates, rather than suppresses, innate and adaptive immune responses. Such responses culminate into T cell-driven immunity against antigens derived from dying cancer cells. The potency of ICD is dependent on the immunogenicity of dying cells as defined by the antigenicity of these cells and their ability to expose immunostimulatory molecules like damage-associated molecular patterns (DAMPs) and cytokines like type I interferons (IFNs). Moreover, it is crucial that the host's immune system can adequately detect the antigenicity and adjuvanticity of these dying cells. Over the years, several well-known chemotherapies have been validated as potent ICD inducers, including (but not limited to) anthracyclines, paclitaxels, and oxaliplatin. Such ICD-inducing chemotherapeutic drugs can serve as important combinatorial partners for anti-cancer immunotherapies against highly immuno-resistant tumors. In this Trial Watch, we describe current trends in the preclinical and clinical integration of ICD-inducing chemotherapy in the existing immuno-oncological paradigms.

CD73 and PD-L1 dual blockade amplifies antitumor efficacy of SBRT in murine PDAC models

BACKGROUND

Stereotactic body radiotherapy (SBRT) induces immunogenic cell death, leading to subsequent antitumor immune response that is in part counterbalanced by activation of immune evasive processes, for example, upregulation of programmed cell death-ligand 1 (PD-L1) and adenosine generating enzyme, CD73. CD73 is upregulated in pancreatic ductal adenocarcinoma (PDAC) compared with normal pancreatic tissue and high expression of CD73 in PDACs is associated with increased tumor size, advanced stage, lymph node involvement, metastasis, PD-L1 expression and poor prognosis. Therefore, we hypothesized that blockade of both CD73 and PD-L1 in combination with SBRT might improve antitumor efficacy in an orthotopic murine PDAC model.

METHODS

We assessed the combination of systemic blockade of CD73/PD-L1 and local SBRT on tumor growth in primary pancreatic tumors, and investigated systemic antitumor immunity using a metastatic murine model bearing both orthotopic primary pancreatic tumor and distal hepatic metastases. Immune response was quantified by flow cytometric and Luminex analyses.

RESULTS

We demonstrated that blockade of both CD73 and PD-L1 significantly amplified the antitumor effect of SBRT, leading to superior survival. The triple therapy (SBRT+anti-CD73+anti-PD-L1) modulated tumor-infiltrating immune cells with increases of interferon-γ+CD8+ T cells. Additionally, triple therapy reprogramed the profile of cytokines/chemokines in the tumor microenvironment toward a more immunostimulatory phenotype. The beneficial effects of triple therapy are completely abrogated by depletion of CD8+ T cells, and partially reversed by depletion of CD4+ T cells. Triple therapy promoted systemic antitumor responses illustrated by: (1) potent long-term antitumor memory and (2) enhanced both primary and liver metastases control along with prolonged survival.

Abscopal Effect on Bone Metastases from Solid Tumors: A Systematic Review and Retrospective Analysis of Challenge within a Challenge

BACKGROUND

Abscopal effect (AE) describes the ability of radiotherapy (RT) to induce immune-mediated responses in nonirradiated distant metastasis. Bone represents the third most frequent site of metastasis and an immunologically favorable environment for the proliferation of cancer cells. We revised the literature, searching documented cases of AE involving bone metastases (BMs) and evaluated the incidence of AE involving BMs in patients requiring palliative RT on BMs or non-BMs treated at our department.

METHODS

Articles published in the PubMed/MEDLINE database were selected using the following search criteria: ((abscopal effect)) AND ((metastases)). Patients with BMs, who underwent performed bone scintigraphy before and at least 2-3 months after RT, were selected and screened between January 2015 and July 2022. AE was defined as an objective response according to the scan bone index for at least one nonirradiated metastasis at a distance > 10 cm from the irradiated lesion. The primary endpoint was the rate of AE on BMs.

RESULTS

Ten cases experiencing AE of BMs were identified from the literature and eight among our patients.

CONCLUSIONS

The analysis performed here suggests the use of hypofractionated radiotherapy as the only triggering factor for AE of BMs through the activation of the immune response.

Microwave ablation induces abscopal effect via enhanced systemic antitumor immunity in colorectal cancer

Background

Thermal ablation is the primary procedure for the local treatment of lung metastases. It is known that radiotherapy and cryoablation can stimulate an abscopal effect, while the occurrence of abscopal effect induced by microwave ablation is less; the cellular and molecular mechanisms involved in the abscopal effect after microwave ablation should be further elucidated.

Methods

CT26 tumor-bearing Balb/c mice were treated with microwave ablation with several combinations of ablation power and time duration. The growth of primary or abscopal tumors and the survival of mice were both monitored; moreover, immune profiles in abscopal tumors, spleens, and lymph nodes were examined by flow cytometry.

Results

Microwave ablation suppressed tumor growth in both primary and abscopal tumors. Both local and systemic T-cell responses were induced by microwave ablation. Furthermore, the mice exhibiting significant abscopal effect after microwave ablation markedly elevated Th1 cell proportion both in the abscopal tumors and spleens.

Conclusions

Microwave ablation at 3 w-3 min not only suppressed tumor growth in the primary tumors but also stimulated an abscopal effect in the CT26-bearing mice via the improvement of systemic and intratumoral antitumor immunity.

Stereotactic Ablative Radiotherapy in the Treatment of Early-Stage Lung Cancer - A Done Deal?

Stereotactic ablative radiotherapy (SABR) is an important curative-intent treatment option for early-stage non-small cell lung cancer. It offers good cancer control without invasive surgery and has become the standard of care for medically inoperable patients. The literature on SABR for early-stage non-small cell lung cancer is substantial and continues to grow. However, there remain areas of controversy where data are limited - notably the use of SABR in medically operable patients. Other areas of some debate include the treatment of central/ultra-central and large (>5 cm) lesions, as well as treatment with co-existing interstitial lung disease. This review article provides an overview of the current literature together with a discussion of future directions.

The Role of Stereotactic Radiotherapy in the Management of Melanoma, A Retrospective Single Institute Preliminary Study of 30 Patients

Cutaneous melanoma is the third most common type of skin cancer in the world. The incidence of melanoma is increasing in most countries, however, mortality seems to be slowly decreasing. The treatment of advanced cutaneous melanoma changed radically since 2011. The new therapeutic modalities, such as immuno- and targeted therapies give a chance to successfully reach more prolonged progression-free survival (PFS) and overall survival (OS) in patients with metastatic melanoma. Despite the great therapeutic benefit, most patients eventually develop resistance to these therapies, and the disease will progress. In some cases oligoprogression develops. In those cases local therapy, such as stereotactic radiotherapy can make it possible to continue the previously applied effective medical treatment for the benefit of patients. In our study of a total of 30 patients—20 of them received pre-treatment with systemic medical therapy—received stereotactic radiotherapy using various systems, in the National Institute of Oncology, Hungary, Budapest. We managed to prolong the systemic therapy for 12.5 months median period with the assistance of CyberKnife technique. Therapy related adverse events were mostly tolerable with only 3% of Grade 3 toxicity. We concluded that stereotactic radiotherapy and stereotactic radiosurgery, are safe, and effective therapeutic modalities for regional tumor control in cases of oligoprogression.

Interaction of Radiotherapy and Hyperthermia with the Immune System: a Brief Current Overview

Purpose of Review

This review focuses on the opposing effects on the immune system of radiotherapy (RT) and the consequences for combined cancer treatment strategies of RT with immunotherapies, including hyperthermia (HT). How RT and HT might affect cancer stem cell populations is also briefly outlined in this context.

Recent Findings

RT is one of the crucial standard cancer therapies. Most patients with solid tumors receive RT for curative and palliative purposes in the course of their disease. RT achieves a local tumor control by inducing DNA damage which can lead to tumor cell death. In recent years, it has become evident that RT does not only have local effects, but also systemic effects which involves induction of anti-tumor immunity and possible alteration of the immunosuppressive properties of the tumor microenvironment. Though, often RT alone is not able to induce potent anti-tumor immune responses since the effects of RT on the immune system can be both immunostimulatory and immunosuppressive.

Summary

RT with additional therapies such as HT and immune checkpoint inhibitors (ICI) are promising approaches to induce anti-tumor immunity effectively. HT is not only a potent sensitizer for RT, but it might also improve the efficacy of RT and certain chemotherapeutic agents (CT) by additionally sensitizing resistant cancer stem cells (CSCs).

Graphical abstract

Long-term control of melanoma adrenal metastasis treated with radiotherapy

Melanoma remains a large global burden with a significant proportion of patients succumbing to metastatic disease. The adrenal gland is a common area for metastasis with surgical treatment as the main modality. Radiotherapy is less utilised in this setting with uncertainty over deliverability and efficacy. Here, we present the details and outcomes of 20 patients treated with radiotherapy, with or without systemic therapy, for melanoma adrenal metastasis in a single institute. Twenty patients were identified from radiation treatment and medical records from between 2015 and 2019 at our institution. Three patients had bilateral radiotherapy treatments and therefore 23 adrenal lesions were analysed. Demographics, indications for treatment, radiotherapy methodology and outcomes were recorded. Outcomes were based on serial 18F FDG PET/computerized tomography scans reporting using the PERCIST criteria. The most common indication for radiotherapy was oligo-progressive disease (70%) followed by symptom palliation. Eight (35%) of the treatments were delivered by stereotactic ablative body radiotherapy. Twelve (60%) patients had concurrent immunotherapy. Twenty of twenty-three (87%) adrenal lesions had an initial response to treatment with 12 (60%) maintaining local control until death or end of follow-up. Median adrenal-specific progression-free survival was 13 months. Four patients (17%) required salvage adrenalectomy. Symptom palliation was achieved in the majority of patients for which it was indicated and there were no grade three toxicities. The median time from radiotherapy to change of immunotherapy treatment was 4 months. Radiotherapy for melanoma adrenal metastasis is effective and deliverable. With the majority of patients achieving a palliative and clinically relevant durable response, adrenalectomy can be reserved as a salvage option.

A Patient-Level Data Meta-analysis of the Abscopal Effect

Purpose

The abscopal effect is defined when a form of local therapy causes tumor regression of both the target lesion and any untreated tumors. Herein cases of the abscopal effect were systematically reviewed and a patient-level data analysis was performed for clinical predictors of both duration of response and survival.

Methods and Materials

The Population, Intervention, Control, Outcome, Study (PICOS) design approach, Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) literature selection process, and Meta-analysis of Observational Studies in Epidemiology (MOOSE) were used to find articles published before September 2019 in MEDLINE/PubMed and Google Scholar. Inclusion criteria were (1) population: patients with reported abscopal response; (2) intervention: documented treatment(s); (3) control: none; (4) outcomes: overall and progression-free survival; and (5) setting: retrospective case reports. Time from treatment until abscopal response and time from abscopal response until progression/death were calculated. Univariate and multivariate analyses were conducted for survival outcomes.

Results

Fifty studies (n = 55 patients) were included. Median age was 65 years (interquartile range [IQR], 58-70) and 62% were male. Fifty-four (98%) patients received radiation therapy, 34 (62%) received radiation therapy alone, 5 (9.1%) underwent surgery, 4 (7.3%) received chemotherapy, and 11 (20%) received immunotherapy. Median total dose was 32 Gy (IQR, 25.5-48 Gy) and median dose per fraction was 3 Gy (IQR, 2-7.2). Median time until abscopal response was 4 months (IQR, 1-5; min 0.5, max 24). At 5 years, overall survival was 63% and distant progression-free survival was 45%. No variables had statistical significance in predicting duration of response or survival.

Conclusions

Almost all reported cases of the abscopal response are after radiation therapy; however, there are no known predictors of duration of response or survival in this population.

Combining Radiotherapy and Immunotherapy in Metastatic Breast Cancer: Current Status and Future Directions

The role of radiotherapy and immunotherapy with immune checkpoint inhibitors (ICI) is of emerging interest in many solid tumours, including breast cancer. There is increasing evidence that the host’s immune system plays an important role in influencing the response to treatment and prognosis in breast cancer. Several pre-clinical studies and clinical trials have reported on the ‘abscopal effect—regression of distant untreated tumour sites, mediated by an immunological response following ionizing radiation to a targeted tumour site. Stereotactic Ablative Body Radiotherapy (SABR) is a non-invasive technique used to augment various immune responses with an ablative tumoricidal dose when compared to conventional radiotherapy. SABR is characterized by typically 1–5 precision radiotherapy treatments that simultaneously deliver a high dose, whilst sparing normal tissues. Following SABR, there is evidence of systemic immune activation in patients with increased PD1 expression on CD8+ and CD4+ T cells. Studies continue to focus on metastatic triple-negative disease, a highly immunogenic subtype of breast cancer with poor prognosis. In this review, we discuss the immunological effect of SABR, alone and in combination with immunotherapy, and the importance of dose and fractionation. We also propose future strategies for treating oligometastatic disease, where this approach may be most useful for producing durable responses.

Radiation Induced Abscopal Effect in a Patient With Malignant Pleural Mesothelioma on Pembrolizumab

Abscopal effect is a rare phenomenon in which treatment benefit from radiotherapy (RT) is seen outside the target field due to activation of the immune system inducing an anti-tumor effect. This phenomenon has been reported in cancer patients receiving immune checkpoint inhibitors (ICI). Here we report a case of presumed abscopal effect in malignant mesothelioma. The patient received second-line single-agent pembrolizumab however had disease progression after four cycles leading to palliative RT (20 Gray) to the right mainstem bronchus. Follow-up radiographic imaging confirmed benefit and pembrolizumab was continued. Follow-up computed tomography (CT) five months after RT, showed marked radiographic improvement of all measurable diseases with improvement in right-sided aerated lung volume. Because of the original disease progression on pembrolizumab, with marked improvements within and outside the RT field after RT, treatment response was presumed due to the abscopal effect.

Recent Research on Combination of Radiotherapy with Targeted Therapy or Immunotherapy in Head and Neck Squamous Cell Carcinoma: A Review for Radiation Oncologists

Radiotherapy plays an important role of managing head and neck squamous cell carcinoma (HNSCC). Concurrent radiotherapy with radiosensitizing cisplastin chemotherapy is the standard of care (SOC) for non-operable locally advanced HNSCC. Cetuximab, a monoclonal antibody of epidermal growth factor receptor, was the most extensively studied targeted therapy as a chemo-sparing agent that was used concurrently with radiotherapy. Immunotherapy is used in the treatment of metastatic HNSCC. There is evidence to support the synergistic effect when combining radiotherapy with immunotherapy to potentiate anti-tumor immune response. There has been increasing interest to incorporate immune checkpoint inhibitor (ICI) with radiotherapy in the curative setting for HNSCC. In this review, we discuss the latest evidence that supports concurrent radiotherapy with cisplatin which remains the SOC for locally advanced HNSCC (LA-HNSCC). Cetuximab is suitable for patients who are not fit for cisplatin. We then summarize the clinical trials that incorporate ICI with radiotherapy for LA-HNSCC in concurrent, neoadjuvant, and adjuvant settings. We also discuss the potential of combining immunotherapy with radiotherapy as a treatment de-escalating strategy in HPV-associated oropharyngeal carcinoma. Finally, the pre-clinical and clinical evidence of the abscopal effect when combining stereotactic body radiotherapy with ICIs is presented.

True abscopal effect in a patient with metastatic non-small cell lung cancer

Background

Systemic response to local anticancer treatment is a phenomenon called ‘abscopal effect’. The immune system is thought to play a pivotal role in its occurrence. To date, several cases have been reported, particularly in patients receiving combined local treatment and immune checkpoint inhibitors. In such cases, it is impossible to discriminate between the effects of local and systemic treatment. Only a few cases of abscopal effect have been described with radiotherapy alone.

Case presentation

Here, we report on the case of an 81-year-old woman with recurrent metastatic squamous cell carcinoma of the lung with mediastinal tumor bulk, lymph node and bone metastases. The patient refused to undergo systemic treatment, and palliative stereotactic radiotherapy of the mediastinal tumor was performed. At restaging with FDG-PET/CT, the patient presented with a decrease in size and FDG-avidity both of the irradiated site and of the lymph node and bone metastases (which did not receive radiotherapy). At 25 months after radiotherapy, the patient is still in remission at all sites.

Conclusions

This is a rare case of an abscopal effect after radiotherapy as monotherapy. It is one of the few hitherto reported for lung cancer. Several ongoing studies with a combination of radiotherapy and immunotherapy are seeking to exploit a potential synergy to induce abscopal effects.

Local ablative therapies in oligometastatic NSCLC-upfront or outback?-a narrative review

Patients with oligometastatic (OM) non-small cell lung cancer (NSCLC) have favorable outcomes compared to patients presenting with diffuse metastatic disease. Recent randomized trials have demonstrated safety and efficacy signals for local ablative therapies with radiotherapy, surgery, or radiofrequency ablation for OM-NSCLC patients alongside systemic therapies. However, it remains unclear whether local ablative therapy (LAT) should be offered either upfront preceding systemic therapies or following initial systemic therapies as local consolidative therapy (LCT). Establishing optimal timing of RT and systemic therapy combinations is essential to maximize efficacy while maintaining safety. Most published randomized trial evidence surrounding the benefits of LAT and systemic therapies were generated from OM-NSCLC patients receiving cytotoxic chemotherapy agents. With increasing use of novel agents such as targeted therapies (i.e., tyrosine kinase inhibitors) and immune checkpoint inhibitors in management of metastatic NSCLC patients, LAT timing may need to be modulated based on the use of specific agents. This narrative review will discuss the current evidence on either upfront LAT or LCT for OM-NSCLC based on published trials and cohort studies. We briefly explored the possible biological mechanisms of the potential clinical advantages of either approach. This review also summarized the ongoing trials incorporating both upfront LAT and LCT, and considerations for future LAT strategies.

Intracranial response after extracranial radiation in a patient with rapidly progressing metastatic melanoma

Growing literature supports the synergistic effect of radiation as a primer for renewed enhanced systemic immunological responses in patients receiving immunotherapy for metastatic melanoma. Radiographic regression of extracranial tumours after treatment of intracranial metastatic lesions has been reported and these observations point to an abscopal effect that traverses the blood-brain barrier. We describe a patient with rapidly progressing metastatic melanoma despite combined immune checkpoint blockade, who achieved a complete metabolic response of both his extracranial and intracranial disease after the commencement of palliative radiation to his axilla. This is the first published case, to our knowledge, of a sustained, complete intracranial abscopal response from extracranial radiation. We discuss potential mechanistic relations between radiation, the blood-brain barrier and the abscopal effect.

A narrative review of combined stereotactic ablative radiotherapy and immunotherapy in metastatic non-small cell lung cancer

Immune checkpoint inhibitors (ICIs) have significantly improved overall survival (OS) in metastatic non-small cell lung cancer (m-NSCLC). However, not all patients with m-NSCLC benefit from ICIs, and resistance to ICIs is an emerging challenge. The tumour microenvironment (TME) is immunosuppressive, and provides a myriad of mechanisms to facilitate escape of cancer cells from immune surveillance. The TME may also dampen the response to ICIs by inhibiting T cell effector responses. The poor prognosis of m-NSCLC has led to investigation of ICIs combined with other treatments with the intention of modulating the TME and sensitizing tumours to the effects of ICIs. Stereotactic ablative radiotherapy (SABR) in combination with ICIs is an area of intense interest. SABR is thought to evoke a pro-immunogenic response in the TME, with the capacity to turn a “cold”, unresponsive tumour to “hot” and receptive to ICI. In addition to improved local response, SABR is postulated to produce a heightened systemic immune response when compared to conventional radiotherapy (RT). Preclinical studies have demonstrated a synergistic effect of SABR + ICIs, and clinical studies in m-NSCLC showed safety and promising efficacy compared to systemic therapies alone. To optimize ICI + SABR, ICI choice, combinations, dosing and length of treatment, as well as sequencing of ICI + SABR all require further investigation. Appropriate sequencing may depend on the ICI(s) being utilized, with differing sites of metastases possibly eliciting differing immune responses. Single versus multisite radiation is controversial, whilst effects of irradiated tumour volume and nodal irradiation are increasingly recognized. Taken together, there is strong preclinical and biological rationale, with emerging clinical evidence, supporting the strategy of combining SABR + ICIs in m-NSCLC.

Thermal ablation in non-small cell lung cancer: a review of treatment modalities and the evidence for combination with immune checkpoint inhibitors

Lung cancer is the leading cause of cancer death worldwide, with approximately 1.6 million cancer related deaths each year. Prognosis is best in patients with early stage disease, though even then five-year survival is only 55% in some groups. Median survival for advanced non-small cell lung cancer (NSCLC) is 8–12 months with conventional treatment. Immune checkpoint inhibitor (ICI) therapy has revolutionised the treatment of NSCLC with significant long-term improvements in survival demonstrated in some patients with advanced NSCLC. However, only a small proportion of patients respond to ICI, suggesting the need for further techniques to harness the potential of ICI therapy. Thermal ablation utilizes the extremes of temperature to cause tumour destruction. Commonly used modalities are radiofrequency ablation (RFA), cryoablation and microwave ablation (MWA). At present thermal ablation is reserved for curative-intent therapy in patients with localized NSCLC who are unable to undergo surgical resection or stereotactic ablative body radiotherapy (SABR). Limited evidence suggests that thermal ablative modalities can upregulate an anticancer immune response in NSCLC. It is postulated that thermal ablation can increase tumour antigen release, which would initiate and upregulated steps in the cancer immunity cycle required to elicit an anticancer immune response. This article will review the current thermal ablative techniques and their ability to modulate an anti-cancer immune response with a view of using thermal ablation in conjunction with ICI therapy.

Valproic acid triggers radiation-induced abscopal effect by modulating the unirradiated tumor immune microenvironment in a rat model of breast cancer

An abscopal effect occurs when localized radiotherapy causes the regression of tumors distant from the irradiated site. However, such a clinically detectable abscopal effect from radiotherapy alone is rare. This study investigated whether valproic acid ([VPA], a histone deacetylase inhibitor [HDACi]) treatment can stimulate radiation-induced abscopal effect. We used 7,12-dimethylbenz[a]anthracene, a typical environmental carcinogen, to establish a rat model with multiple breast tumors. Only one tumor received 8 Gy fractionated doses of X-rays (2 Gy daily fractions over four days) and 200 mg/kg VPA was administered intraperitoneally. We monitored the growth of both irradiated and unirradiated tumors after treatments. The unirradiated tumor was collected for hematoxylin and eosin (HE) staining, immunohistochemistry (IHC) (CD8, Granzyme B, Cleaved Caspase-3, BrdU, Ki67, F4/80 and CD68), double immunofluorescence (F4/80 and CD86), Western blot (Cleaved Caspase-3) and qRT-PCR (CD86, CD163, IL-1β, IL-6, IL-12, IL-23, IL-10, TGF-β) analysis. We found ionizing radiation (IR) + VPA treatment inhibited both irradiated and unirradiated tumor growth as compared to IR alone. Such observe abscopal effect was mediated by the recruitment of activated CD8+ T cells into the unirradiated tumor sites, which released Granzyme B to cause tumor cell apoptosis. Furthermore, IR + VPA treatment led to macrophages infiltration into the unirradiated tumor sites and polarization to M1 phenotype, resulted in increased levels of pro-inflammatory cytokines such as IL-1β and IL-12, and decreased levels of anti-inflammatory cytokines such as IL-10 and TGF-β. Our data supports the proposition that VPA may be a potential therapeutic candidate to trigger radiation-induced abscopal effect by modulating the unirradiated tumor immune microenvironment.

Radiotherapy and the immune system: More than just immune suppression

Radiotherapy (RT) is still one of the standard cancer therapies, with up to two third of all cancer patients with solid tumors being irradiated in the course of their disease. The aim of using ionizing radiation in fractionated treatment schedules was always to achieve local tumor control by inducing DNA damage which can be repaired by surrounding normal tissue but leads to cell death in tumor cells. Meanwhile, it is known that RT also has immunological effects reshaping the tumor microenvironment. Nevertheless, RT alone often fails to elicit potent antitumor immune responses as these effects can be immunostimulatory as well as immunosuppressive. Here, we discuss how immunotherapies can be exploited in combined therapies to boost RT-induced antitumor immune responses or to counteract preexisting and RT-mediated immunosuppression to improve local and systemic tumor control. Furthermore, we highlight some parameters of radioimmunotherapies (RITs) which are under investigation for potential optimizations and how RIT approaches are tested in first phases II and III trials. Finally, we discuss how RT might affect normal and cancer stem cells.

Atypical Response Patterns in Renal Cell Carcinoma Treated with Immune Checkpoint Inhibitors-Navigating the Radiologic Potpourri

BACKGROUND

Atypical response patterns have been a topic of increasing relevance since the advent of immune checkpoint inhibitors (ICIs), challenging the traditional RECIST (Response Evaluation Criteria in Solid Tumors) method of tumor response assessment. Newer immune-related response criteria can allow for the evolution of radiologic pseudoprogression, but still fail to capture the full range of atypical response patterns encountered in clinical reporting.

METHODS

We did a detailed lesion-by-lesion analysis of the serial imaging of 46 renal cell carcinoma (RCC) patients treated with ICIs with the aim of capturing the full range of radiologic behaviour.

RESULTS

Atypical response patterns observed included pseudoprogression (n = 15; 32.6%), serial pseudoprogression (n = 4; 8.7%), dissociated response (n = 22; 47.8%), abscopal response (n = 9; 19.6%), late response (n = 5; 10.9%), and durable response after cessation of immunotherapy (n = 2; 4.3%). Twenty-four of 46 patients (52.2%) had at least one atypical response pattern and 18 patients (39.1%) had multiple atypical response patterns.

CONCLUSIONS

There is a high incidence of atypical response patterns in RCC patients receiving ICIs and the study contributes to the growing literature on the abscopal effect. The recognition of these interesting and overlapping radiologic patterns challenges the oncologist to tweak treatment options such that the clinical benefits of ICIs are potentially maximized.

Controversies in the role of radiotherapy in pleural mesothelioma

Malignant pleural mesothelioma is an uncommon thoracic cancer with a relatively poor outcome, which has only seen modest improvements when compared to non-small cell lung cancer. The mainstays of treatment have been surgery and systemic therapy, with radiation reserved for palliation or as an adjunct. However, there is re-emergent interest in the use of radiotherapy in the treatment of mesothelioma, given recent technical advances in radiotherapy delivery which permit increased treatment accuracy. This overview article reviews the radiobiology of the mesothelioma and whether or not mesothelioma is an inherently radioresistant cancer and the potential impact that hypofractionation may have on different histological subtypes in mesothelioma. This overview also considers the role of radiation in palliation, as adjunct to surgical resection and as adjunct to pleural tract procedures. In particular we review the growing evidence that pleural tract or port site adjuvant radiotherapy provides no clinical benefit. This overview will also consider potential emerging therapeutic strategies such as pre-operative short course hypofractionated radiotherapy. The role of novel radiotherapy techniques such as stereotactic ablative radiotherapy, image guided radiotherapy, proton therapy and the potential role of radiotherapy as an immune stimulating agent in combination of immunotherapy, will also be discussed. Finally, given the many unanswered questions, this review discusses some of the emerging and ongoing clinical trials of radiotherapy in the treatment of mesothelioma.

Advances in Hypofractionated Irradiation-Induced Immunosuppression of Tumor Microenvironment

Hypofractionated radiotherapy is external beam irradiation delivered at higher doses in fewer fractions than conventional standard radiotherapy, which can stimulate innate and adaptive immunity to enhance the body’s immune response against cancer. The enhancement effect of hypofractionated irradiation to immune response has been widely investigated, which is considered an approach to expand the benefit of immunotherapy. Meanwhile, increasing evidence suggests that hypofractionated irradiation may induce or enhance the suppression of immune microenvironments. However, the suppressive effects of hypofractionated irradiation on immunomicroenvironment and the molecular mechanisms involved in these conditions are largely unknown. In this context, we summarized the immune mechanisms associated with hypofractionated irradiation, highlighted the advances in its immunosuppressive effect, and further discussed the potential mechanism behind this effect. In our opinion, besides its immunogenic activity, hypofractionated irradiation also triggers homeostatic immunosuppressive mechanisms that may counterbalance antitumor effects. And this may suggest that a combination with immunotherapy could possibly improve the curative potential of hypofractionated radiotherapy.

Combined Radiotherapy and New Systemic Therapies - Have We Moved Beyond Palliation?

The new systemic therapies for cancer are having major impacts on the prognosis of patients with advanced cancers, some achieving long-term survival with targeted therapy or immune checkpoint inhibitors. Interactions of radiotherapy with the new systemic therapies are reviewed. Many agents increase radiosensitivity and particular caution is required combining BRAF inhibitors and radiotherapy because of significant toxicity. Most new systemic therapies can be used safely with palliative doses of radiotherapy, but it is important to be aware of overlapping toxicities depending on the site treated. DNA damage response modulators increase radiosensitivity and may potentially increase radiation toxicity but are at an earlier stage of development. Stereotactic ablative radiotherapy may produce further survival gains in patients responding to targeted therapy and immunotherapy.

Stereotactic ablative radiotherapy for colorectal cancer liver metastasis

Survival improvement of colorectal liver metastasis (CRLM) benefits from systemic therapy and metastasis-directed local therapy. Stereotactic ablative body radiotherapy (SABR), as a new efficient metastasis-directed local therapy with a systematic impact, plays a vital role in CRLM multidisciplinary treatment. SABR leads to a dramatic immunological change in the tumor microenvironment (TME) via differential activation of cytoprotective and cytotoxic pathways in malignant and non-malignant cells, in addition to direct tumor cell death. The synergy of SABR and immunotherapy might increase the abscopal response rate of out-field lesions by targeting different steps of the immune-mediated response, in addition to direct intratumoral cell death. The clinical treatment and efficacy of SABR, its influence on TME, and potential molecular underpinnings of which are the topic of this review.

Radiobiology of stereotactic ablative radiotherapy (SABR): perspectives of clinical oncologists

Stereotactic ablative radiotherapy (SABR) is a novel radiation treatment method that delivers an intense dose of radiation to the treatment targets with high accuracy. The excellent local control and tolerance profile of SABR have made it become an important modality in cancer treatment. The radiobiology of SABR is a key factor in understanding and further optimizing the benefits of SABR. In this review, we have addressed several issues in the radiobiology of SABR from the perspective of clinical oncologists. The appropriateness of the linear-quadratic (LQ) model for SABR is controversial based on preclinical data, but it is a reliable tool from the perspective of clinical application because the biological effective dose (BED) calculated with it can represent the tumor control probability (TCP). Hypoxia is a common phenomenon in SABR in spite of the relatively small tumor size and has a negative effect on the efficacy of SABR. Preliminary studies indicate that a hypoxic radiosensitizer combined with SABR may be a feasible strategy, but so far there is not adequate evidence to support its application in routine practice. The vascular change of endothelial apoptosis and blood perfusion reduction in SABR may enhance the response of tumor cells to radiation. Combination of SABR with anti-angiogenesis therapy has shown promising efficacy and good tolerance in advanced cancers. SABR is more powerful in enhancing antitumor immunity and works better with immune checkpoint inhibitors (ICIs) than conventional fractionation radiotherapy. Combination of SABR with ICIs has become a practical option for cancer patients with metastases.

Abscopal effect in radioimmunotherapy

Abscopal effect is an interesting phenomenon in radiobiology that causes activation of immune system against cancer cells. Traditionally, this phenomenon was known as a suppressor of non-irradiated tumors or metastasis. However, it can be used as a stimulator of the immune system against primary tumor during radiotherapy. Immunotherapy, a novel tumor therapy modality, also triggers immune system against cancer. To date, some immunotherapy types have been developed. However, immune checkpoint blockade is a more common modality and some drugs have been approved by the FDA. Studies have shown that radiotherapy or immunotherapy administered alone have low efficiency for tumor control. However, their combination has a more potent anti-tumor immunity. For this aim, it is important to induce abscopal effect in primary tumors, and also use appropriate drugs to target the mechanisms involved in the exhaustion of cytotoxic CD8+T lymphocytes (CTLs) and natural killer (NK) cells. Among the different radiotherapy techniques, stereotactic body radiation therapy (SBRT) with some few fractionations is the best choice for inducing abscopal effect. On the other hand, programmed cell death 1 (PD-1) is known as one of the best targets for triggering anti-tumor immunity. This combination is known as the best choice among various strategies for radioimmunotherapy. However, there is the need for other strategies to improve the duration of immune system's activity within tumor microenvironment (TME). In this review, we explain the cellular and molecular mechanisms behind abscopal effect by radiotherapy and evaluate the molecular targets which induce potent anti-tumor immunity.

When Should we Irradiate the Primary in Metastatic Lung Cancer?

Metastatic lung cancer encompasses a heterogenous group of patients in terms of burdens of disease, ranging from patients with extensive metastases to those with a limited number of metastatic lesions (oligometastatic disease). Histopathological heterogeneity also exists within two broad categories, non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), portraying different patterns and evolution of disease. Local consolidative therapy to the primary tumour and metastatic sites, including surgery and/or radical dose radiotherapy, is increasingly being used to improve survival outcomes, particularly in the context of oligometastatic disease, with or without the use of molecular targeted therapy and immunotherapy. Recently, randomised studies in oligometastatic NSCLC have shown that local consolidative therapy may confer a survival advantage. This review explores whether treating just the primary tumour with radiotherapy may similarly produce improved clinical outcomes. Such a treatment strategy may carry less potential toxicity than treating multiple sites upfront. The biological rationale behind the potential benefits of treating just the primary in metastatic malignancy is discussed. The clinical evidence of such an approach across tumour sites, such as breast and prostate cancer, is also explored. Then the review focuses on treating the primary in NSCLC and SCLC with radiotherapy, by first exploring patterns of failure in metastatic NSCLC and second exploring evidence on survival outcomes from studies in metastatic NSCLC and SCLC. It is challenging to draw conclusions on the clinical benefit of treating the primary cancer in isolation from the evidence available. This highlights the need to collect data within the ongoing clinical trials on the clinical outcome and toxicity of radiotherapy delivery to primary thoracic disease specifically. This challenge also identifies the need to design future clinical trials to produce randomised evidence for such an approach.