Involvement of the kynurenine pathway in breast cancer: updates on clinical research and trials

Breast cancer (BrCa) is the leading cause of cancer incidence and mortality in women worldwide. While BrCa treatment has been shown to be highly successful if detected at an early stage, there are few effective strategies to treat metastatic tumours. Hence, metastasis remains the main cause in most of BrCa deaths, highlighting the need for new approaches in this group of patients. Immunotherapy has been gaining attention as a new treatment for BrCa metastasis and the kynurenine pathway (KP) has been suggested as one of the potential targets. The KP is the major biochemical pathway in tryptophan (TRP) metabolism, catabolising TRP to nicotinamide adenine dinucleotide (NAD+). The KP has been reported to be elevated under inflammatory conditions such as cancers and that its activity suppresses immune surveillance. Dysregulation of the KP has previously been reported implicated in BrCa. This review aims to discuss and provide an update on the current mechanisms involved in KP-mediated immune suppression and cancer growth. Furthermore, we also provide a summary on 58 studies about the involvement of the KP and BrCa and five clinical trials targeting KP enzymes and their outcome.

Regulatory cells and the effect of cancer immunotherapy

Several mechanisms and cell types are involved in the regulation of the immune response. These include mostly regulatory T cells (Tregs), regulatory macrophages (Mregs), myeloid suppressor cells (MDSCs) and other regulatory cell types such as tolerogenic dendritic cells (tolDCs), regulatory B cells (Bregs), and mesenchymal stem cells (MSCs). These regulatory cells, known for their ability to suppress immune responses, can also suppress the anti-tumor immune response. The infiltration of many regulatory cells into tumor tissues is therefore associated with a poor prognosis. There is growing evidence that elimination of Tregs enhances anti-tumor immune responses. However, the systemic depletion of Treg cells can simultaneously cause deleterious autoimmunity. Furthermore, since regulatory cells are characterized by their high level of expression of immune checkpoints, it is also expected that immune checkpoint inhibitors perform part of their function by blocking these molecules and enhancing the immune response. This indicates that immunotherapy does not only act by activating specific effector T cells but can also directly or indirectly attenuate the suppressive activity of regulatory cells in tumor tissues. This review aims to draw together our current knowledge about the effect of immunotherapy on the various types of regulatory cells, and how these effects may be beneficial in the response to immunotherapy.

Kynureninase Upregulation Is a Prominent Feature of NFR2-Activated Cancers and Is Associated with Tumor Immunosuppression and Poor Prognosis

The nuclear factor erythroid 2-related factor 2 (NRF2) pathway is frequently activated in various cancer types. Aberrant activation of NRF2 in cancer is attributed to gain-of-function mutations in the NRF2-encoding gene NFE2L2 or a loss of function of its suppressor, Kelch-like ECH-associated protein 1 (KEAP1). NRF2 activation exerts pro-tumoral effects in part by altering cancer cell metabolism. Previously, we reported a novel mechanism of NRF2 tumoral immune suppression through the selective upregulation of the tryptophan-metabolizing enzyme kynureninase (KYNU) in lung adenocarcinoma. In the current study, we explored the relevance of NRF2-mediated KYNU upregulation across multiple cancer types. Specifically, using a gene expression dataset for 9801 tumors representing 32 cancer types from The Cancer Genome Atlas (TCGA), we demonstrated that elevated KYNU parallels increased gene-based signatures of NRF2-activation and that elevated tumoral KYNU mRNA expression is strongly associated with an immunosuppressive tumor microenvironment, marked by high expression of gene-based signatures of Tregs as well as the immune checkpoint blockade-related genes CD274 (PDL-1), PDCD1 (PD-1), and CTLA4, regardless of the cancer type. Cox proportional hazard models further revealed that increased tumoral KYNU gene expression was prognostic for poor overall survival in several cancer types, including thymoma, acute myeloid leukemia, low-grade glioma, kidney renal papillary cell carcinoma, stomach adenocarcinoma, and pancreatic ductal adenocarcinoma (PDAC). Using PDAC as a model system, we confirmed that siRNA-mediated knockdown of NRF2 reduced KYNU mRNA expression, whereas activation of NFE2L2 (the coding gene for NRF2) through either small-molecule agonists or siRNA-mediated knockdown of KEAP1 upregulated KYNU in PDAC cells. Metabolomic analyses of the conditioned medium from PDAC cell lines revealed elevated levels of KYNU-derived anthranilate, confirming that KYNU was enzymatically functional. Collectively, our study highlights the activation of the NRF2-KYNU axis as a multi-cancer phenomenon and supports the relevance of tumoral KYNU as a marker of tumor immunosuppression and as a prognostic marker for poor overall survival.

Medical Therapy for Craniopharyngiomas

Craniopharyngiomas are rare benign neoplasms presenting in two different types, adamantinomatous (ACP) or papillary (PCP), which are molecularly and clinically distinct. Traditional treatment includes surgical resection and radiotherapy, which are accompanied by a number of debilitating complications because of the tumours' proximity to important brain structures. Recent advances in the understanding of molecular pathogenesis of craniopharyngiomas have opened horizons to medical therapeutic options. ACPs are mainly characterized by mutations of β-catenin, which activate Wingless/Int (Wnt), and alter the mitogen extracellular kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway, as well as inflammatory, cellular senescence, programmed cell death and sonic hedgehog (SHH) pathways. PCPs are mainly characterized by Ras/Raf/MEK/ERK pathway activation secondary to BRAF-V600E mutations. MEK inhibitors, such as binimetinib, or anti-inflammatory mediators, such as tocilizumab or interferon, have been administered to patients with ACP and the efficacy is mostly favourable. On the other hand, BRAF inhibitors, such as dabrafenib or vemurafenib, either alone or in combination with the MEK inhibitors trametinib and cobimetinib, have been administered to patients with PCP resulting in favourable responses. A number of ongoing trials will shed light on schemes, doses, combined treatments and safety issues of the new molecular-targeted treatments, changing the management of patients with craniopharyngiomas by launching the era of personalized medicine in these rare neoplasms. We conducted a systematic review to identify case series or case reports with patients currently treated with systemic medical therapy.

Recent advances in clinical trials targeting the kynurenine pathway

The kynurenine pathway (KP) is the major catabolic pathway for the essential amino acid tryptophan leading to the production of nicotinamide adenine dinucleotide. In inflammatory conditions, the activation of the KP leads to the production of several bioactive metabolites including kynurenine, 3-hydroxykynurenine, 3-hydroxyanthranilic acid, kynurenic acid and quinolinic acid. These metabolites can have redox and immune suppressive activity, be neurotoxic or neuroprotective. While the activity of the pathway is tightly regulated under normal physiological condition, it can be upregulated by immunological activation and inflammation. The dysregulation of the KP has been implicated in wide range of neurological diseases and psychiatric disorders. In this review, we discuss the mechanisms involved in KP-mediated neurotoxicity and immune suppression, and its role in diseases of our expertise including cancer, chronic pain and multiple sclerosis. We also provide updates on the clinical trials evaluating the efficacy of KP inhibitors and/or analogues in each respective disease.

Involvement of Kynurenine Pathway in Hepatocellular Carcinoma

Simple Summary

The kynurenine pathway (KP) is a biochemical pathway that synthesizes the vital coenzyme, nicotinamide adenine dinucleotide (NAD⁺). In cancer, the KP is significantly activated, leading to tryptophan depletion and the production of downstream metabolites, which skews the immune response towards tumour tolerance. More specifically, advanced stage cancers that readily metastasize evidence the most dysregulation in KP enzymes, providing a clear link between the KP and cancer morbidity. Consequently, this provides the rationale for an attractive new drug discovery opportunity for adjuvant therapeutics targeting KP-mediated immune tolerance, which would greatly complement current pharmacological interventions. In this review, we summarize recent developments in the roles of the KP and clinical trials examining KP inhibition in liver cancer.

Abstract

As the second and third leading cancer-related death in men and the world, respectively, primary liver cancer remains a major concern to human health. Despite advances in diagnostic technology, patients with primary liver cancer are often diagnosed at an advanced stage. Treatment options for patients with advanced hepatocarcinoma (HCC) are limited to systemic treatment with multikinase inhibitors and immunotherapy. Furthermore, the 5-year survival rate for these late-stage HCC patients is approximately 12% worldwide. There is an unmet need to identify novel treatment options and/or sensitive blood-based biomarker(s) to detect this cancer at an early stage. Given that the liver harbours the largest proportion of immune cells in the human body, understanding the tumour–immune microenvironment has gained increasing attention as a potential target to treat cancer. The kynurenine pathway (KP) has been proposed to be one of the key mechanisms used by the tumour cells to escape immune surveillance for proliferation and metastasis. In an inflammatory environment such as cancer, the KP is elevated, suppressing local immune cell populations and enhancing tumour growth. In this review, we collectively describe the roles of the KP in cancer and provide information on the latest research into the KP in primary liver cancer.

The immunotherapeutic role of indoleamine 2,3-dioxygenase in head and neck squamous cell carcinoma: A systematic review

BACKGROUND

Novel cancer immunotherapy seeks to harness the body's own immune system and tip the balance in favour of antitumour activity. The intracellular enzyme indoleamine 2,3-dioxygenase (IDO) is a critical regulator of the tumour microenvironment (TME) via tryptophan metabolism. The potential immunotherapeutic role of IDO in head and neck squamous cell carcinoma (HNSCC) requires further exploration. We aim to assess the evidence on IDO in HNSCC.

METHODS

A systematic review of literature and clinical trials databases.

RESULTS

We included 40 studies: seven involved cell lines: eight assessed tumour immunohistochemistry: ten measured IDO gene transcription: 15 reported on clinical trials. Increased cell line IDO expression was postulated to adversely affect tumour metabolism and apoptosis. Immunohistochemical IDO expression correlated with worse survival. Gene transcription studies associated IDO with positive PD-L1 and human papillomavirus (HPV) status. Phase I/II clinical trials showed (a) overall response (34%-55%) and disease control rates (62%-70%) for IDO1 inhibitor in combination with a PD-1 inhibitor, (b) similar safety profiles when both are used in combination therapy compared to each as monotherapies and (c) IDO gene expression as a predictive biomarker for response to PD-L1 therapy.

CONCLUSIONS

IDO expression is increased in the TME of HNSCC, which correlates with poor prognosis. However, the exact mechanism of IDO-driven immune modulation in the TME is an enigma. Future translational studies should map IDO activity during HNSCC treatment and elucidate its precise role in the TME, such research will underpin the development of clinical trials establishing the efficacy of IDO inhibitors in HNSCC.

The footprint of kynurenine pathway in every cancer: a new target for chemotherapy

Treatment of cancers has always been a challenge for physicians. Typically, several groups of anti-cancer medications are needed for effective management of an invasive and metastatic cancer. Recently, therapeutic potentiation of immune system markedly improved treatment of cancers. Kynurenine pathway has an interwoven correlation with immune system. Kynurenine promotes T Reg (regulatory) differentiation, which leads to increased production of anti-inflammatory cytokines and suppression of cytotoxic activity of T cells. Overactivation of kynurenine pathway in cancers provides an immunologically susceptible microenvironment for mutant cells to survive and invade surrounding tissues. Interestingly, kynurenine pathway vigorously interacts with other molecular pathways involved in tumorigenesis. For instance, kynurenine pathway interacts with phospoinosisitide-3 kinase (PI3K), extracellular signal-regulated kinase (ERK), Wnt/β-catenin, P53, bridging integrator 1 (BIN-1), cyclooxygenase 2 (COX-2), cyclin-dependent kinase (CDK) and collagen type XII α1 chain (COL12A1). Overactivation of kynurenine pathway, particularly overactivation of indoleamine 2,3-dioxygenase (IDO) predicts poor prognosis of several cancers such as gastrointestinal cancers, gynecological cancers, hematologic malignancies, breast cancer, lung cancer, glioma, melanoma, prostate cancer and pancreatic cancer. Furthermore, kynurenine increases the invasion, metastasis and chemoresistance of cancer cells. Recently, IDO inhibitors entered clinical trials and successfully passed their safety tests and showed promising therapeutic efficacy for cancers such as melanoma, brain cancer, renal cell carcinoma, prostate cancer and pancreatic cancer. However, a phase III trial of epacadostat, an IDO inhibitor, could not increase the efficacy of treatment with pembrolizumab for melanoma. In this review the expanding knowledge towards kynurenine pathway and its application in each cancer is discussed separately.

Manipulation of Inflammasome: A Promising Approach Towards Immunotherapy of Lung Cancer

Chronic inflammation has emerged as a key player at different stages of cancer development. A prominent signaling pathway for acute and chronic inflammation is the activation of the caspase-1 inflammasomes. These are complexes that assemble on activation of certain nucleotide-binding domain, leucine-rich repeat containing proteins (NLRs), AIM2-like receptors (ALRs), or pyrin due to activation via PAMPs or DAMPs. Of these, five complexes-NLRP1, NLRP3, NLRC4, Pyrin, and AIM2 are of importance in the context of cancer for their activities in modulating immune responses, cell proliferation, and apoptosis. Inflammasomes have emerged as clinically relevant in multiple forms of cancer making them highly promising targets for cancer therapy. As lungs are a tissue niche that is prone to inflammation owing to its exposure to external substances, inflammasomes play a vital role in the development and pathogenesis of lung cancer. Therefore, manipulation of inflammasome by various immunomodulatory means could prove a full-proof strategy for the treatment of lung cancer. Here, in this review, we tried to explore the various strategies to target the inflammasomes for the treatment of lung cancer.

Immuno-Metabolism and Microenvironment in Cancer: Key Players for Immunotherapy

Immune checkpoint inhibitors (ICIs) have changed therapeutic algorithms in several malignancies, although intrinsic and secondary resistance is still an issue. In this context, the dysregulation of immuno-metabolism plays a leading role both in the tumor microenvironment (TME) and at the host level. In this review, we summarize the most important immune-metabolic factors and how they could be exploited therapeutically. At the cellular level, an increased concentration of extracellular adenosine as well as the depletion of tryptophan and uncontrolled activation of the PI3K/AKT pathway induces an immune-tolerant TME, reducing the response to ICIs. Moreover, aberrant angiogenesis induces a hypoxic environment by recruiting VEGF, T_reg cells and immune-suppressive tumor associated macrophages (TAMs). On the other hand, factors such as gender and body mass index seem to affect the response to ICIs, while the microbiome composition (and its alterations) modulates both the response and the development of immune-related adverse events. Exploiting these complex mechanisms is the next goal in immunotherapy. The most successful strategy to date has been the combination of antiangiogenic drugs and ICIs, which prolonged the survival of patients with non-small-cell lung cancer (NSCLC) and hepatocellular carcinoma (HCC), while results from tryptophan pathway inhibition studies are inconclusive. New exciting strategies include targeting the adenosine pathway, TAMs and the microbiota with fecal microbiome transplantation.

Targeting indoleamine-2,3-dioxygenase in cancer: Scientific rationale and clinical evidence

Immunotherapy through immune checkpoint blockers (ICBs) is quickly transforming cancer treatment by improving patients' outcomes. However, innate and acquired resistance to ICBs remain a major challenge in clinical settings. Indoleamine 2,3-dioxygenases (IDOs) are enzymes involved in tryptophan catabolism with a central immunosuppressive function within the tumor microenvironment. IDOs are over-expressed in cancer patients and have increasingly been associated with worse outcomes and a poor prognosis. Preclinical data have shown that combining IDO and checkpoint inhibition might be a valuable strategy to improve the efficacy of immunotherapy. Currently, several IDO inhibitors have been evaluated in clinical trials, showing favorable pharmacokinetic profiles and promising efficacy. This review describes the mechanisms involved in IDO-mediated immune suppression and its role in cancer immune escape, focusing on the potential clinical application of IDO inhibitors as an immunotherapy strategy for cancer treatment.

Indoleamine 2,3-Dioxygenase (IDO) Inhibition as a Strategy to Augment Cancer Immunotherapy

Indoleamine 2,3-dioxygenase (IDO) is an enzyme of interest in immuno-oncology because of the immunosuppressive effects that result from its role in tryptophan catabolism. IDO is upregulated in malignancy and is associated with poor prognosis in multiple cancer types. IDO inhibitors have been developed to target IDO, both directly and indirectly. Pre-clinical data have shown combined IDO and checkpoint inhibition to be an efficacious strategy for tumor control. Clinical trials of IDO inhibitors with chemotherapy or immunotherapy are currently underway. This review describes the function of IDO and its inhibitors and summarizes the efficacy and toxicity data from recent clinical trials with these drugs.

Updates in the Clinical Development of Epacadostat and Other Indoleamine 2,3-Dioxygenase 1 Inhibitors (IDO1) for Human Cancers

Recent application of immunotherapy in clinical oncology revolutionized our management of advanced human cancers. Check point inhibitors targeting CTLA4 and PD-1/PD-L1 axis are immunotherapeutic agents currently available to treat a variety of cancers. However, a novel therapeutic approach is needed to further improve patient outcome with these agents. Indoleamine 2,3-dioxygenase 1 (IDO1) is a rate-limiting enzyme in the metabolism of essential amino acid tryptophan in the peripheral tissue. IDO1 is overexpressed in human cancer cells and suppresses effector T cell function and promotes regulatory T cells (Tregs). Overexpression of IDO1 is associated with poor patient survival in several types of human cancer. These findings indicate that IDO1 is a promising target that can improve the treatment outcome in the field of Immuno-oncology. Several orally available IDO1 inhibitors including Epacadostat have entered human clinical trials over the last few years without a major safety concern. Although there is no objective response in single-agent trials, combination regimens with PD-1 inhibitors appear to exceed the activity of PD-1 inhibitors alone. Recent phase III ECHO 301 trial testing the combination of Epacadostat with Pembrolizumab in melanoma did not show superior outcome compared to Pembrolizumab alone. This lead to halting of other phase III trials using IDO1 inhibitors. In this minireview, we will discuss the recent clinical development of Epacadostat and other IDO1 inhibitors.

Targeting metabolic vulnerabilities of cancer: Small molecule inhibitors in clinic

BACKGROUND

Altered cell metabolism is an established hallmark of cancer. Advancement in our understanding of dysregulated cellular metabolism has aided drastically in identifying metabolic vulnerabilities that can be exploited therapeutically. Indeed, this knowledge has led to the development of a multitude of agents targeting various aspects of tumor metabolism.

RECENT FINDINGS

The intent of this review is to provide insight into small molecule inhibitors that target tumor metabolism and that are currently being explored in active clinical trials as either preventive, stand-alone, or adjuvant therapies for various malignancies. For each inhibitor, we outline the mechanism (s) of action, preclinical/clinical findings, and limitations. Sections are divided into three aspects based on the primary target of the small molecule inhibitor (s): those that impact (1) cancer cells directly, (2) immune cells present in the tumor microenvironment, or (3) both cancer cells and immune cells. We highlight small molecule targeting of metabolic pathways including de novo fatty acid synthesis, NAD+ biosynthesis, 2-hydroxyglutarate biosynthesis, polyamine metabolism, the kynurenine pathway, as well as glutamine and arginine metabolism.

CONCLUSIONS

Use of small molecule inhibitors aimed at exploiting tumor metabolic vulnerabilities continues to be an active area of research. Identifying metabolic dependencies specific to cancer cells and/or constituents of the tumor microenvironment is a viable area of therapeutic intervention that holds considerable clinical potential.

Hepatotoxicity of immune checkpoint inhibitors: An evolving picture of risk associated with a vital class of immunotherapy agents

Immune checkpoint inhibitors (ICIs) block CTLA-4, PD-1 and PD-L1, or other molecules that control antitumour activities of lymphocytes. These products are associated with a broad array of immune-related toxicities affecting a variety of organs, including the liver. ICI-associated immune-mediated hepatitis (IMH) ranges in severity between mild and life-threatening and is marked by findings that bear both similarities as well as differences with idiopathic autoimmune hepatitis. Hepatotoxic events are often detected in clinical trials of ICIs that are powered for efficacy. Risk levels for ICI-induced liver injury may be impacted by the specific checkpoint molecule targeted for treatment, the ICI dose levels, and the presence of a pre-existing autoimmune diathesis, chronic infection or tumour cells which infiltrate the liver parenchyma. When patients develop liver injury during ICI treatment, a prompt assessment of the cause of injury, in conjunction with the application of measures to optimally manage the adverse event, should be made. Strategies to manage the risk of IMH include the performance of pretreatment liver tests with regular monitoring during and after ICI treatment and patient education. Using Common Terminology Criteria for Adverse Events developed at the National Cancer Institute to measure the severity level of liver injury, recommended actions may include continued ICI treatment with close patient monitoring, ICI treatment suspension or discontinuation and/or administration of corticosteroids or, when necessary, a non-steroidal immunosuppressive agent. The elucidation of reliable predictors of tumour-specific ICI treatment responses, as well as an increased susceptibility for clinically serious immune-related adverse events, would help optimize treatment decisions for individual patients.

Next generation of immune checkpoint therapy in cancer: new developments and challenges

Immune checkpoints consist of inhibitory and stimulatory pathways that maintain self-tolerance and assist with immune response. In cancer, immune checkpoint pathways are often activated to inhibit the nascent anti-tumor immune response. Immune checkpoint therapies act by blocking or stimulating these pathways and enhance the body's immunological activity against tumors. Cytotoxic T lymphocyte-associated molecule-4 (CTLA-4), programmed cell death receptor-1 (PD-1), and programmed cell death ligand-1(PD-L1) are the most widely studied and recognized inhibitory checkpoint pathways. Drugs blocking these pathways are currently utilized for a wide variety of malignancies and have demonstrated durable clinical activities in a subset of cancer patients. This approach is rapidly extending beyond CTLA-4 and PD-1/PD-L1. New inhibitory pathways are under investigation, and drugs blocking LAG-3, TIM-3, TIGIT, VISTA, or B7/H3 are being investigated. Furthermore, agonists of stimulatory checkpoint pathways such as OX40, ICOS, GITR, 4-1BB, CD40, or molecules targeting tumor microenvironment components like IDO or TLR are under investigation. In this article, we have provided a comprehensive review of immune checkpoint pathways involved in cancer immunotherapy, and discuss their mechanisms and the therapeutic interventions currently under investigation in phase I/II clinical trials. We also reviewed the limitations, toxicities, and challenges and outline the possible future research directions.

Cancer immunotherapy beyond immune checkpoint inhibitors

Malignant cells have the capacity to rapidly grow exponentially and spread in part by suppressing, evading, and exploiting the host immune system. Immunotherapy is a form of oncologic treatment directed towards enhancing the host immune system against cancer. In recent years, manipulation of immune checkpoints or pathways has emerged as an important and effective form of immunotherapy. Agents that target cytotoxic T lymphocyte-associated molecule-4 (CTLA-4), programmed cell death receptor-1 (PD-1), and programmed cell death ligand-1 (PD-L1) are the most widely studied and recognized. Immunotherapy, however, extends beyond immune checkpoint therapy by using new molecules such as chimeric monoclonal antibodies and antibody drug conjugates that target malignant cells and promote their destruction. Genetically modified T cells expressing chimeric antigen receptors are able to recognize specific antigens on cancer cells and subsequently activate the immune system. Native or genetically modified viruses with oncolytic activity are of great interest as, besides destroying malignant cells, they can increase anti-tumor activity in response to the release of new antigens and danger signals as a result of infection and tumor cell lysis. Vaccines are also being explored, either in the form of autologous or allogenic tumor peptide antigens, genetically modified dendritic cells that express tumor peptides, or even in the use of RNA, DNA, bacteria, or virus as vectors of specific tumor markers. Most of these agents are yet under development, but they promise to be important options to boost the host immune system to control and eliminate malignancy. In this review, we have provided detailed discussion of different forms of immunotherapy agents other than checkpoint-modifying drugs. The specific focus of this manuscript is to include first-in-human phase I and phase I/II clinical trials intended to allow the identification of those drugs that most likely will continue to develop and possibly join the immunotherapeutic arsenal in a near future.

Pembrolizumab as first-line therapy for metastatic non-small-cell lung cancer

This review describes trials evaluating the monoclonal antibody pembrolizumab (an immunotherapy that blocks the interaction between programmed death-1 and programmed death-ligand 1 and 2 [PD-L1/PD-L2]) as first-line therapy for advanced non-small-cell lung cancer (NSCLC). In the Phase III KEYNOTE-024 study, pembrolizumab monotherapy significantly improved progression-free survival (primary end point) and overall survival, and was associated with fewer adverse events compared with platinum-based chemotherapy in patients with NSCLC with PD-L1 expression on ≥50% of tumor cells. In cohort G of the Phase I/II KEYNOTE-021 study, pembrolizumab plus pemetrexed and carboplatin significantly improved objective response rate (primary end point) and progression-free survival versus pemetrexed and carboplatin alone, and had manageable toxicity in patients with nonsquamous NSCLC. These results have changed first-line management of advanced NSCLC.

Targeting immune checkpoints in breast cancer: an update of early results

The immune tumour microenvironment has been shown to play a crucial role in the development and progression of cancer. Expression of gene signatures, reflecting immune activation, and the presence of tumour-infiltrating lymphocytes were associated with favourable outcomes in HER2-positive and triple-negative breast cancer. Recently, immunotherapy with immune checkpoint blockade induced long-lasting responses and improved survival in hard-to-treat malignancies (ie, melanoma and non-small cell lung cancer) and are changing treatment paradigms in a variety of neoplastic diseases. Immune checkpoint blockade has been evaluated in breast cancer, particularly in the triple-negative subtype, with promising results observed in monotherapy or in combination with chemotherapy in the metastatic and neoadjuvant settings. However, identification of patients who are most likely to benefit from immune checkpoint blockade remains challenging, with many patients not responding to treatments and a significant financial cost. The combination of immune checkpoint blockade with conventional cancer treatments such as chemotherapy, radiotherapy, targeted therapies or with other immunotherapies is a promising strategy to potentiate its efficacy in breast cancer although further research is required to effectively identify who will respond to these immunotherapies. In this review we report the most recent results that emerged from trials testing immune checkpoint blockade and potential predictive biomarkers and emphasise the new strategies that are under clinical development in breast cancer.

Checkpoint inhibitors in melanoma and early phase development in solid tumors: what's the future?

Anti-programmed death (PD)-1 and PD-ligand (L)-1 checkpoint inhibitors have revolutionized the therapy of several cancers. Immunotherapy of cancer can offer long-term durable benefit to patients, is active regardless of tumour histology, has a unique immune-related safety profile, and can be used in combination with other cancer treatments. In addition, recent research has shown that immune-based therapy can be used as adjuvant therapy, that outcomes may be influenced by dose, and that clinical activity is observed in patients with brain metastases. Despite our increased understanding of these agents, there are still several important questions that need to be answered. These include strategies to overcome primary and acquired resistance, the influence of mutational status on treatment outcomes, the optimal duration of treatment, and the need to identify novel combination regimens that offer increased anti-tumour potency and/or reduced toxicity. Here we review recent developments in these areas, with particular focus on new data reported at the 2017 ASCO Annual Meeting.