Methods of harnessing the immune system to treat cancer have been investigated for decades, but yielded little clinical progress. However, in recent years, novel drugs that allow immune recognition and destruction of tumor cells are emerging as potent cancer therapies. Building upon previous immunotherapy strategies that included therapeutic vaccines, recombinant cytokines, and other immunostimulatory agents, newer immunotherapy agents targeting immune checkpoints including programmed cell death 1, programmed cell death ligand-1, and cytotoxic T-lymphocyte-associated protein 4, among others, have garnered substantial enthusiasm after demonstrating clinical activity in a broad spectrum of tumor types. Trials evaluating immune checkpoint inhibitors in metastatic non-small-cell lung cancer (NSCLC) demonstrate robust and durable responses in a subset of patients. However, with overall response rates less than 20%, combinatorial strategies that extend the benefit of these agents to more patients are desirable. The integration of radiotherapy with immunotherapy is a conceptually promising strategy, as radiotherapy has potent immunomodulatory effects and may contribute not only to local control but may also augment systemic antitumor immune response. Preclinical data and case reports suggest the potential for robust clinical responses in metastatic NSCLC patients using this strategy, but prospective clinical trials evaluating the integration of radiation and immunotherapy are limited. The use of immunotherapy in nonmetastatic settings is also intriguing but understudied. We review the potential clinical settings of interest for the partnering of immunotherapy and radiation in NSCLC, including early stage, locally advanced, and metastatic disease, and review completed, accruing, and developing clinical trials.

Purpose

Increased rates of toxicity have been described after stereotactic body radiation therapy (SBRT) for central lung tumors within 2 cm of the proximal bronchial tree (PBT). Recent studies have defined a new class of ultracentral tumors. We report our experience treating ultracentral, central, and paramediastinal tumors with SBRT and compare toxicity, disease control, and survival rates.

Methods and materials

We reviewed the records of patients with central lung tumors treated with SBRT between September 2009 and July 2017. Tumors were classified as central if within 2 cm of the PBT, ultracentral if the planning target volume touched the PBT or esophagus, and paramediastinal if touching mediastinal pleura. Actuarial rates of grades 2+ and 3+ toxicity, local control (LC), and overall survival were assessed using the Kaplan-Meier method and compared using a log-rank test. Toxicity was scored with the Common Terminology Criteria for Adverse Events, version 4.03.

Results

We identified 68 patients with 69 central lung tumors, including 14 ultracentral, 15 paramediastinal, and 39 central tumors. Fifty-three patients were treated for early stage lung cancer and 15 for lung metastases. The prescribed dose ranged from 40 Gy to 60 Gy over 3 to 8 fractions. Most patients were treated using 5 fractions (83%), followed by 8 fractions (10%). Median follow-up was 19.7 months (range, 3.3-78.3 months). The 2-year estimates of LC (89%, 85%, and 93%, respectively; P = .72) and overall survival (76%, 73%, and 72%, respectively; P = .75) for ultracentral, central, and paramediastinal tumors were similar. Ultracentral tumors had an increased risk of grade 2+ toxicity (57.6% vs 14.2% vs 7.1%; P = .007) at 2 years. One patient with an ultracentral tumor developed grade 5 respiratory failure.

Conclusions

The oncologic outcomes after SBRT for ultracentral, central, and paramediastinal lung tumors were similar, with LC exceeding 85% at 2 years using predominantly 5-fraction schedules. Ultracentral lung tumors were associated with an increased risk of toxicity in our patient cohort. Additional studies are needed to minimize toxicity for ultracentral tumors.

The development of immunotherapy is an important breakthrough for the treatment of cancer, with antitumor efficacy observed in a wide variety of tumors. To optimize immunotherapy use, approaches must be developed to identify which patients are likely to achieve benefit. To minimize therapeutic toxicities and costs, understanding the ideal choice and sequencing of the numerous immuno-oncology agents available for individual patients is thus critical, but fraught with challenges. The immune tumor microenvironment (TME) is a unique aspect of the response to immuno-oncology agents and measurement of single biomarkers does not adequately capture these complex interactions. Therefore, multiple potential biomarkers are likely needed. Current candidates in this area include PD-L1 expression, CD8⁺ tumor-infiltrating lymphocytes, tumor mutation load and neoantigen burden, immune-related gene signatures, and multiplex IHC assays that examine the pharmacodynamic and spatial interactions of the TME. The most fruitful investigations are likely to use several techniques to predict response and interrogate mechanisms of resistance. Immuno-oncology biomarker research must employ validated assays to ask focused research questions utilizing clinically annotated tissue collections and biomarker-focused clinical trial designs to investigate specific endpoints. Real-time input from patients and their advocates into biomarker discovery is necessary to ensure that the investigations pursued will improve both clinical outcomes and quality of life. We herein provide a framework of recommendations to guide the search for immuno-oncology biomarkers of value.

A malignant tumor consists of malignant cells as well as a wide array of normal host tissues including stroma, vasculature, and immune infiltrate. The interaction between cancer and these host tissues is critical as these host tissues play a variety of roles in supporting or resisting disease progression. Radiotherapy (RT) has direct effects on malignant cells, but, also, critically important effects on these other components of the tumor microenvironment (TME). Given the growing role of immune checkpoint inhibitors and other immunotherapy strategies, understanding how RT affects the TME, particularly the immune compartment, is essential to advance RT in this new era of cancer therapy. The interactions between RT and the TME are complex, affecting the innate and adaptive arms of the immune system. RT can induce both proinflammatory effects and immune suppressive effects that can either promote or impede antitumor immunity. It is likely that the initial proinflammatory effects of RT eventually lead to rebound immune-suppression as chronic inflammation sets in. The exact kinetics and nature of how RT changes the TME likely depends on timing, dose, fractionation, site irradiated, and tumor type. With increased understanding of the effects of RT on the TME, in the future it is likely that we will be able to personalize RT by varying the dose, site, and timing of intervention to generate the desired response to partner with immunotherapy strategies.

Three dimensional (3D) scanning and printing technology is utilized to create phantom models of mice in order to assess the accuracy of ionizing radiation dosing from a clinical, human-based linear accelerator. Phantoms are designed to simulate a range of research questions, including irradiation of lung tumors and primary subcutaneous or orthotopic tumors for immunotherapy experimentation. The phantoms are used to measure the accuracy of dose delivery and then refine it to within 1% of the prescribed dose.

Not until the turn of this century has immunotherapy become a fundamental component of cancer treatment. While monotherapy with immune modulators, such as immune checkpoint inhibitors, provides a subset of patients with durable clinical benefit and possible cure, combination therapy offers the potential for antitumor activity in a greater number of patients. The field of immunology has provided us with a plethora of potential molecules and pathways to target. This abundance makes it impractical to empirically test all possible combinations efficiently. We recommend that potential immunotherapy combinations be chosen based on sound rationale and available data to address the mechanisms of primary and acquired immune resistance. Novel trial designs may increase the proportion of patients receiving potentially efficacious treatments and, at the same time, better define the balance of clinical activity and safety. We believe that implementing a strategic approach in the early development of immunotherapy combinations will expedite the delivery of more effective therapies with improved safety and durable outcomes.

Immune checkpoint inhibition (ICI) has emerged as one of the most powerful tools to reverse cancer induced immune suppression. Monoclonal antibodies (mAbs) targeting programmed cell death 1/programmed cell death ligand 1(PD-1/PD-L1) are FDA-approved and their clinical use is rapidly expanding. As opposed to the clinical paradigm, which can result in significant responses and toxicities, it has been difficult to reproduce these effects preclinically using mouse models. In large part, this is due to models, which employ rapidly growing ex vivo cultured transplantable tumor cell lines engrafted into young naïve inbred laboratory mice. However, another issue concerns the use and repeated application of xenogeneic reagents in mice (i.e., rat or hamster mAbs directed against mouse antigens at variance with clinical use of human or humanized mAbs). Building on our previous studies demonstrating that repeated administration of commonly used xenogeneic anti-PD-1 mAbs derived from both rat and hamster can induce fatal hypersensitivity in some tumor-bearing mice, we sought to compare these result with the effects of a mouse anti-mouse PD-1 mAb. Application of a murine anti-mouse PD-1 (clone: MuDX400) did not result in lethal anaphylaxis in the 4T1 tumor model. It also displayed superior antitumor effects in this and other tumor models, as it did not induce neutralizing antibody responses against the anti-PD-1 mAb, such as were observed when using xenogeneic anti-PD1 mAbs. These results demonstrate that more accurate preclinical modeling necessitates the use of mouse reagents mirroring the clinical scenario to ascertain long-term effects or toxicities, while avoiding xenogeneic responses, which do not occur clinically. Furthermore, these studies suggest a direct mechanism, whereby preclinical murine studies have often failed to recapitulate the clinical efficacy and toxicity of single agent checkpoint inhibition.

Radiation therapy (RT) is advocated in the multimodal treatment of high-grade soft tissue sarcoma (STS), but its role may be less clear in chemotherapy-sensitive STS such as extraskeletal Ewing sarcoma (EES). The purpose of this study was to determine the role of RT on overall survival (OS) in localized EES adult patients treated with chemotherapy and surgery. Adult patients diagnosed with EES and reported to the National Cancer Database from 2004 to 2014 were evaluated. All patients were treated with surgical resection. Patient demographics, tumor characteristics, treatments received, resection margins, and survival were examined for the 232 patients identified. Using multivariate analysis and Cox proportional hazard analysis, predictors of OS were determined. In the overall cohort, 40 percent of patients received RT and 78 percent received chemotherapy, with 31 percent receiving both. The addition of RT to the patients receiving surgery + chemotherapy did not improve OS (p < 0.05). Twenty-four percent of patients who achieved R0 resection after surgery still received RT without any improvement in OS. Patients treated at community cancer centers were more likely to receive additional RT compared with Comprehensive Cancer Centers (p < 0.05). In adult EES patients with localized disease treated with chemotherapy and surgery, the addition of RT does not improve overall survival.

Novel ligands that target Toll-like receptors and other innate recognition pathways represent a potent strategy for modulating innate immunity to generate antitumor immunity. Although many of the current clinically successful immunotherapies target adaptive T-cell responses, both preclinical and clinical studies suggest that adjuvants have the potential to enhance the scope and efficacy of cancer immunotherapy. Radiation may be a particularly good partner to combine with innate immune therapies, because it is a highly efficient means to kill cancer cells but may fail to send the appropriate inflammatory signals needed to act as an efficient endogenous vaccine. This may explain why although radiation therapy is a highly used cancer treatment, true abscopal effects-regression of disease outside the field without additional systemic therapy-are extremely rare. This review focuses on efforts to combine innate immune stimuli as adjuvants with radiation, creating a distinct and complementary approach from T cell-targeted therapies to enhance antitumor immunity.

Background

Radiation therapy (RT) is a standard component in the multimodality management of localized soft tissue sarcoma (STS). Increasing studies are focusing on biological modifiers that may influence the host's response to RT, including immunologic mechanisms known to change with the aging process. We hypothesized that the effects of RT would be influenced by age, contributing to differences in treatment outcome.

Methods

Using Surveillance, Epidemiology, and End Results (1990-2011), we identified 30,898 adult patients (>18 y) with nonmetastatic STS undergoing initial surgery. We compared patient demographics, tumor characteristics, and treatments by age. Multivariable analyses were used to analyze overall survival (OS) and disease-specific survival (DSS). Hazard ratios (HRs) were calculated based on multivariable Cox proportional hazards models.

Results

Mean age at diagnosis was 56.6 ± 16.8 y, and 33.6% of patients were ≥65 y. Of the total, 52.1% of patients were male and 67% were white; 59.9% of patients underwent surgery alone, 33.3% received adjuvant RT, and 6.8% neoadjuvant RT. On multivariable analysis, age, sex, year of diagnosis, histology, grade, size, marital status, and RT predicted OS, whereas age, year of diagnosis, ethnicity, histology, site, grade, RT, size, and marital status predicted DSS. In all patients, RT was associated with improved OS and DSS compared to surgery alone (median OS 136 ± 13 mo with RT versus 118 ± 9 mo without RT and 5-y OS 63.2 ± 1.4% with RT versus 60.5 ± 1.2% without, P < 0.01). Patients ≥65 y derived greater improvements in OS and DSS compared with patients <65 y. These benefits were most notable after neoadjuvant RT with patients ≥65 y having significantly better OS (HR = 0.63; 95% confidence interval = 0.53-0.75), whereas patients <65 y did not (HR = 0.96; 95% confidence interval = 0.83-1.10). In addition, interaction testing demonstrated a significant modifier effect between RT and age (P < 0.05).

Conclusions

RT is associated with improved survival in patients with STS undergoing surgical treatment, but improvements in oncologic outcome with RT were greatest among older patients. Further studies into the mechanism of these age-related effects are needed.