Mechanisms of Immune-Related Complications in Cancer Patients Treated with Immune Checkpoint Inhibitors

Tocilizumab in the treatment of steroid refractory immune-related hepatotoxicity: a case series and review of the literature

With the widespread use of immune checkpoint inhibitors, management of immune-related adverse effects specific to these treatments became an important research era in patient management. Among these, immune-related hepatotoxicity (IRH) is an adverse event that can be fatal. While the first-line treatment of IRH is well established, there is still no consensus regarding the management approach for steroid-refractory, severe IRH. Here, we report four patients with metastatic melanoma who developed IRH during antiprogrammed cell death protein-1 plus anticytotoxic T-lymphocyte-associated protein-4 combination therapy and review of the literature. All of our patients were steroid-refractory and were successfully treated with tocilizumab. Given the rapid improvement in liver enzymes and patient's clinical status with tocilizumab, this treatment should be prioritized in steroid-refractory IRH.

Immune-Related Adverse Events Due to Cancer Immunotherapy: Immune Mechanisms and Clinical Manifestations

The landscape of cancer treatment has undergone a significant transformation with the introduction of Immune Checkpoint Inhibitors (ICIs). Patients undergoing these treatments often report prolonged clinical and radiological responses, albeit with a potential risk of developing immune-related adverse events (irAEs). Here, we reviewed and discussed the mechanisms of action of ICIs and their pivotal role in regulating the immune system to enhance the anti-tumor immune response. We scrutinized the intricate pathogenic mechanisms responsible for irAEs, arising from the evasion of self-tolerance checkpoints due to drug-induced immune modulation. We also summarized the main clinical manifestations due to irAEs categorized by organ types, detailing their incidence and associated risk factors. The occurrence of irAEs is more frequent when ICIs are combined; with neurological, cardiovascular, hematological, and rheumatic irAEs more commonly linked to PD1/PD-L1 inhibitors and cutaneous and gastrointestinal irAEs more prevalent with CTLA4 inhibitors. Due to the often-nonspecific signs and symptoms, the diagnosis of irAEs (especially for those rare ones) can be challenging. The differential with primary autoimmune disorders becomes sometimes intricate, given the clinical and pathophysiological similarities. In conclusion, considering the escalating use of ICIs, this area of research necessitates additional clinical studies and practical insights, especially the development of biomarkers for predicting immune toxicities. In addition, there is a need for heightened education for both clinicians and patients to enhance understanding and awareness.

Delayed immune-related hepatitis after 24 months of pembrolizumab treatment: a case report and literature review

Immune checkpoint inhibitors targeting the programmed cell death protein 1 (PD-1) pathway have revolutionized cancer immunotherapy by enhancing the immune system's ability to combat cancer cells. However, this innovative approach comes with a distinctive set of challenges, as these therapies can lead to immune-related adverse events (irAEs) due to their mechanism of action. The most common irAEs involve the skin, gastrointestinal tract, liver, endocrine system, and lungs. These events can range from mild skin rashes to severe colitis, pneumonitis, or even autoimmune organ damage. These adverse effects usually appear with an average of 5-15 weeks from the start of treatment depending on the affected organ. This article presents a case report of a delayed related-mediated hepatitis, after 24 months of treatment with pembrolizumab and almost 3 months after its termination, and a review of the scientific literature on cases of delayed immune-related hepatitis caused by anti-PD1. This case highlights the importance of monitoring patients treated with immune checkpoint inhibitors after cessation as a growing number of patients stop treatment due to achieving durable responses.

The JAK-STAT Pathway as a Therapeutic Strategy in Cancer Patients with Immune Checkpoint Inhibitor-Induced Colitis: A Narrative Review

Immunotherapy has emerged as a pivotal component in the treatment of various malignancies, encompassing lung, skin, gastrointestinal, and head and neck cancers. The foundation of this therapeutic approach lies in immune checkpoint inhibitors (ICI). While ICIs have demonstrated remarkable efficacy in impeding the neoplastic progression of these tumours, their use may give rise to substantial toxicity, notably in the gastrointestinal domain, where ICI colitis constitutes a significant aspect. The optimal positioning of Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway inhibitors in the therapeutic management of ICI colitis remains unclear. Numerous reports have highlighted notable improvements in ICI colitis through the application of pan-JAK-STAT inhibitors, with tofacitinib, in particular, reporting evident clinical remission of colitis. The precise mechanism by which JAK-STAT inhibitors may impact the pathogenetic process of ICI colitis remains inadequately understood. However, there is speculation regarding their potential role in modulating memory resident CD8+ T lymphocytes. The elucidation of this mechanism requires further extensive and robust evidence, and ongoing JAK-STAT-based trials are anticipated to contribute valuable insights.

Immune-mediated hepatitis: Basic concepts and treatment

Immunotherapy with immune checkpoint inhibitors (ICIs) has revolutionized advanced cancer management. Nevertheless, the generalized use of these medications has led to an increase in the incidence of adverse immune-mediated events and the liver is one of the most frequently affected organs. Liver involvement associated with the administration of immunotherapy is known as immune-mediated hepatitis (IMH), whose incidence and clinical characteristics have been described by different authors. It often presents as mild elevations of amino transferase levels, seen in routine blood tests, that spontaneously return to normal, but it can also manifest as severe transaminitis, possibly leading to the permanent discontinuation of treatment. The aim of the following review was to describe the most up-to-date concepts regarding the epidemiology, diagnosis, risk factors, and progression of IMH, as well as its incidence in different types of common cancers, including hepatocellular carcinoma. Treatment recommendations according to the most current guidelines are also provided.

The TSP1-CD47-SIRPα interactome: an immune triangle for the checkpoint era

The use of treatments, such as programmed death protein 1 (PD1) or cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) antibodies, that loosen the natural checks upon immune cell activity to enhance cancer killing have shifted clinical practice and outcomes for the better. Accordingly, the number of antibodies and engineered proteins that interact with the ligand-receptor components of immune checkpoints continue to increase along with their use. It is tempting to view these molecular pathways simply from an immune inhibitory perspective. But this should be resisted. Checkpoint molecules can have other cardinal functions relevant to the development and use of blocking moieties. Cell receptor CD47 is an example of this. CD47 is found on the surface of all human cells. Within the checkpoint paradigm, non-immune cell CD47 signals through immune cell surface signal regulatory protein alpha (SIRPα) to limit the activity of the latter, the so-called trans signal. Even so, CD47 interacts with other cell surface and soluble molecules to regulate biogas and redox signaling, mitochondria and metabolism, self-renewal factors and multipotency, and blood flow. Further, the pedigree of checkpoint CD47 is more intricate than supposed. High-affinity interaction with soluble thrombospondin-1 (TSP1) and low-affinity interaction with same-cell SIRPα, the so-called cis signal, and non-SIRPα ectodomains on the cell membrane suggests that multiple immune checkpoints converge at and through CD47. Appreciation of this may provide latitude for pathway-specific targeting and intelligent therapeutic effect.

Machine Learning Approaches for Assessing Risk Factors of Adrenal Insufficiency in Patients Undergoing Immune Checkpoint Inhibitor Therapy

Adrenal insufficiency is a rare, yet life-threatening immune-related adverse event of immune checkpoint inhibitors (ICIs). This study aimed to establish a risk scoring system for adrenal insufficiency in patients receiving anti-programmed cell death 1 (PD-1) or anti-programmed cell death-ligand 1 (PD-L1) agents. Moreover, several machine learning methods were utilized to predict such complications. This study included 209 ICI-treated patients from July 2015 to February 2021, excluding those with prior adrenal insufficiency, previous steroid therapy, or incomplete data to ensure data integrity. Patients were continuously followed up at Gyeongsang National University Hospital, with morning blood samples taken for basal cortisol level measurements, facilitating a comprehensive analysis of their adrenal insufficiency risk. Using a chi-squared test and logistic regression model, we derived the odds ratio and adjusted odds ratio (AOR) through univariate and multivariable analyses. This study utilized machine learning algorithms, such as decision trees, random forests, support vector machines (SVM), and logistic regression to predict adrenal insufficiency in patients treated with ICIs. The performance of each algorithm was evaluated using metrics like accuracy, sensitivity, specificity, precision, and the area under the receiver operating characteristic curve (AUROC), ensuring rigorous assessment and reproducibility. A risk scoring system was developed from the multivariable and machine learning analyses. In a multivariable analysis, proton pump inhibitors (PPIs) (AOR 4.5), and α-blockers (AOR 6.0) were significant risk factors for adrenal insufficiency after adjusting for confounders. Among the machine learning models, logistic regression and elastic net showed good predictions, with AUROC values of 0.75 (0.61-0.90) and 0.76 (0.64-0.89), respectively. Based on multivariable and machine learning analyses, females (1 point), age ≥ 65 (1 point), PPIs (1 point), α-blockers (2 points), and antipsychotics (3 points) were integrated into the risk scoring system. From the logistic regression curve, patients with 0, 1, 2, 4, 5, and 6 points showed approximately 1.1%, 2.8%, 7.3%, 17.6%, 36.8%, 61.3%, and 81.2% risk for adrenal insufficiency, respectively. The application of our scoring system could prove beneficial in patient assessment and clinical decision-making while administering PD-1/PD-L1 inhibitors.

SARS-CoV-2 infection and COVID-19 vaccination in cancer patients undergoing immune checkpoint inhibitors

Cancer patients are susceptible to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Different antitumor treatments have attracted wide attention in the context of coronavirus disease 2019 (COVID-19), especially immune checkpoint inhibitors (ICIs) that have revolutionized oncology changes. It may also have protective and therapeutic roles in viral infections. In this article, we collected 26 cases of SARS-CoV-2 infection during ICIs therapy and 13 related to COVID-19 vaccination from Pubmed, EMBASE, and Wed of Science. Of these 26 cases, 19 (73.1%) presented mild cases and 7 (26.9%) were severe cases. Melanoma (47.4%) was a common cancer type in mild cases and lung cancer (71.4%) in severe cases (P = 0.016). The results showed that their clinical outcomes varied widely. Although there are similarities between the immune checkpoint pathway and COVID-19 immunogenicity, ICIs therapy overactivated T cells, which often leads to immune-related adverse events. In fact, the COVID-19 vaccine has been shown to be safe and effective in patients treated with ICIs. In this review, we report the vital clinical observations of SARS-CoV-2 infection or vaccination in cancer patients treated with ICIs and explore the potential interaction between them.

Case Report: The application of associating liver partition and portal vein ligation for staged hepatectomy in patients with hepatitis b virus-related hepatocellular carcinoma after undergoing treatment with an immune checkpoint inhibitor: a report of two cases

Hepatocellular carcinoma (HCC) is often diagnosed at an unresectable stage without opportunities for curative therapy. Future liver remnant (FLR) insufficiency limits the range of patients who can undergo radical resection. Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) can ultimately achieve short-term hypertrophy of the FLR in patients with viral hepatitis-related fibrosis/cirrhosis and R0 resection. However, the influence of immune checkpoint inhibitors (ICIs) on liver regeneration remains unknown. We report two patients diagnosed with Barcelona Clinic Liver Cancer (BCLC)-B stage hepatitis B virus (HBV)-related HCC who underwent pioneering ALPPS after immunotherapy without posthepatectomy liver failure (PHLF). ALPPS has been shown to be safe and feasible in patients with HCC who underwent immunotherapy previously for the first time and might provide an alternative salvage option for future conversion therapy of HCC.

Changes of peripheral T cell subsets in melanoma patients with immune-related adverse events

Introduction

Immunotherapies have improved the prognosis of many cancer patients including patients with advanced melanoma. Immune checkpoint receptors including CTLA-4 and PD-1 have been established as main therapeutic targets for immunotherapy of melanoma. Although monotherapy is effective in melanoma patients, a dual therapy approach has been shown to be most effective. Dual checkpoint blockade, however, increases substantially the risk for immune-related adverse events (irAEs).

Methods

In this study, we characterized peripheral immune cell subsets in patients with anti-PD-1 monotherapy and with dual immune receptors blockade targeting PD-1 and CTLA-4.

Results

We found differences in peripheral T cells between patients who developed severe immune-related side effects and patients with mild irAEs. We identified several mainly changes in CD8+ T cell subsets in patients with severe irAE under dual PD-1 and CTLA-4 blockade.

Discussion

This work suggests that peripheral immune cell dynamics could be associated with severe immune-related side effects in patients receiving immune checkpoint inhibitors. These changes could be used as future biomarkers in early diagnosis of irAEs.

Configuring Therapeutic Aspects of Immune Checkpoints in Lung Cancer

Immune checkpoints are unique components of the body's defense mechanism that safeguard the body from immune responses that are potent enough to harm healthy body cells. When proteins present on the surface of T cells recognize and bind to the proteins present on other tumor cells, immune checkpoints are triggered. These proteins are called immunological checkpoints. The T cells receive an on/off signal when the checkpoints interact with companion proteins. This might avert the host's immune system from eliminating cancer cells. The standard care plan for the treatment of non-small cell lung cancer (NSCLC) has been revolutionized with the use of drugs targeting immune checkpoints, in particular programmed cell death protein 1. These drugs are now extended for their potential to manage SCLC. However, it is acknowledged that these drugs have specific immune related adverse effects. Herein, we discuss the use of immune checkpoint inhibitors in patients with NSCLC and SCLC, their outcomes, and future perspectives.

Immunogenomic correlates of immune-related adverse events for anti-programmed cell death 1 therapy

Despite impressive antitumor efficacy of programmed cell death 1 (PD-1) inhibitors, this inhibition can induce mild to severe autoimmune toxicities, termed immune-related adverse events (irAEs). Yet, predictive pretreatment biomarkers for irAEs development across cancer types remain elusive. We first assessed cellular and molecular factors. To determine factors predicting the risk of irAEs for anti-PD-1 immunotherapy across multiple cancer types, an integrative analysis of cellular and molecular factors from 9104 patients across 21 cancer types and 4865522 postmarketing adverse event reports retrieved from adverse event reporting system was then performed. Accuracy of predictions was quantified as Pearson correlation coefficient determined using leave-one-out cross-validation. Independent validation sets included small cell lung cancer and melanoma cohorts. Out of 4865522 eligible adverse events reports, 10412 cases received anti-PD-1 monotherapy, of which, 2997 (28.78%) exhibited at least one irAE. Among established immunogenomic factors, dendritic cells (DC) abundance showed the strongest correlation with irAEs risk, followed by tumor mutational burden (TMB). Further predictive accuracy was achieved by DC and TMB in combination with CD4⁺ naive T-cells abundance, and then validated in the small cell lung cancer cohort. Additionally, global screening of multiomics data identified 11 novel predictors of irAEs. Of these, IRF4 showed the highest correlation. Best predictive performance was observed in the IRF4 - TCL1A - SHC-pY317 trivariate model. Associations of IRF4 and TCL1A expression with irAEs development were verified in the melanoma cohort receiving immune checkpoint inhibitors. Collectively, pretreatment cellular and molecular irAEs-associated features as well as their combinations are identified regardless of cancer types. These findings may deepen our knowledge of irAEs pathogenesis and, ultimately, aid in early detection of high-risk patients and management of irAEs.

Optimal timing of steroid initiation in response to CTLA-4 antibody in metastatic cancer: A mathematical model

Immune checkpoint inhibitors, introduced in recent years, have revolutionized the treatment of many cancers. However, the toxicity associated with this therapy may cause severe adverse events. In the case of advanced lung cancer or metastatic melanoma, a significant number (10%) of patients treated with CTLA-4 inhibitor incur damage to the pituitary gland. In order to reduce the risk of hypophysitis and other severe adverse events, steroids may be combined with CTLA-4 inhibitor; they reduce toxicity, but they also diminish the anti-cancer effect of the immunotherapy. This trade-off between tumor reduction and the risk of severe adverse events poses the following question: What is the optimal time to initiate treatment with steroid. We address this question with a mathematical model from which we can also evaluate the comparative benefits of each schedule of steroid administration. In particular, we conclude that treatment with steroid should not begin too early, but also not very late, after immunotherapy began; more precisely, it should start as soon as tumor volume, under the effect of CTLA-4 inhibitor alone, begins to decrease. We can also compare the benefits of short term treatment of steroid at high doses to a longer term treatment with lower doses.

Efficacy and Safety of Immune Checkpoint Inhibitors for Advanced Malignant Melanoma: A Meta-Analysis on Monotherapy Vs Combination Therapy

Background: Immune checkpoint inhibitors (ICIs) are approved as cancer immunotherapeutic agents for advanced malignant melanoma (MM) in recent years, and nivolumab and ipilimumab are the most widely used ICIs either alone or in combination. However, their efficacy and safety between single and combined ICIs are not clear. This meta-analysis (MA) is aimed to update the efficacy and safety of ICIs by comparing monotherapy and combination therapy in the treatment of advanced MM.

Method: We searched PubMed, Embase, EbscoHost and ClinicalTrials.gov for the eligible randomized controlled trials (RCTs) which compared the efficacy and safety of ICIs between a single ICI and combined ICIs. The outcomes analyzed included overall survival (OS), progression-free survival (PFS), objective response rate (ORR) and treatment-related adverse events (AEs). A fixed-effect or random-effects model was adopted depending on the study heterogeneity.

Results: A total of nine RCTs were included in this MA. Regarding the efficacy, combined nivolumab and ipilimumab therapy showed statistically significant prolonged OS and PFS with HR 0.65, 95% CI [0.53, 0.79], p <0.0001 and HR 0.48, 95% CI [0.38, 0.60], p<0.0001 respectively. Combination therapy with nivolumab and ipilimumab also showed statistically significant longer ORR than monotherapy; with RR 2.15, 95% CI [1.63, 2.84], p <0.00001. In terms of safety, the incidence of all AEs which include any AEs, high-grade, haematological, gastrointestinal, dermatological, pulmonary, liver and endocrine AEs were significantly lower with monotherapy (either nivolumab or ipilimumab) of ICI compared to combination ICI therapy with a p-value <0.00001 to 0.03.

Conclusion: Efficacy of the combined nivolumab and ipilimumab was better than a single ICI, especially in the treatment of advanced MM. Although combination therapy showed better efficacy than monotherapy, monotherapy (either nivolumab or ipilimumab) was safer than combination therapy as it tended to decrease the incidence of most of the treatment-related AEs.

Mechanisms of dermatologic toxicities to immune checkpoint inhibitor cancer therapies

The discovery of immune checkpoint inhibition (ICI) sparked a revolution in the era of targeted anticancer therapy. While monoclonal antibodies targeting the CTLA-4 and PD-1 axes have improved survival in patients with advanced cancers, these immunotherapies are associated with a wide spectrum of dermatologic immune-related adverse events (irAEs). Several publications have addressed the clinical and histopathologic classification of these skin-directed irAEs, their impact on antitumor immunity and survival, and the critical role of supportive oncologic dermatology in their management. Here, we review the current understanding of the mechanistic drivers of immune-related skin toxicities with a focus on inflammatory, immunobullous, melanocyte/pigment-related reactions. We detail the specific immune-based mechanisms that may underlie different cutaneous reactions. We also discuss potential mechanisms as they relate to non-cutaneous irAEs and potential overlap with cutaneous irAEs, techniques to study differences in immune-related versus de novo skin reactions, and how treatment of these adverse events impacts cancer treatment, patient quality of life, and overall survival. An improved understanding of the mechanistic basis of cutaneous irAEs will allow us to develop and utilize blood-based biomarkers that could help ultimately predict onset and/or severity of these irAEs and to implement rational mechanistic-based treatment strategies that are targeted to the irAEs while potentially avoiding abrogating anti-tumor effect of ICIs.

Squamous cell carcinoma of the lung: Improving the detection and management of immune-related adverse events

INTRODUCTION

Immune checkpoint inhibitors (ICIs) have revolutionized treatment for patients with non-small lung cancer (NSCLC). Currently approved ICIs are monoclonal antibodies that target programmed death receptor 1 (PD-1), its ligand PD-L1, or CTLA-4. With ICIs comes a novel collection of toxicities: immune-related adverse events (IRAEs). Management of IRAEs requires multidisciplinary expertise. We review the biology of IRAEs and their management in patients with squamous NSCLC.

AREAS COVERED

We review the pathophysiology of ICIs and IRAEs. For IRAEs related to squamous NSCLC, Cochrane Central, EMBASE, and PubMed were queried for trials with patients with squamous cell carcinoma or adenocarcinoma histology, who were assessed for incidence rates of IRAEs. Thirteen trials met inclusion criteria. National guidelines are reviewed to outline management strategies for IRAEs.

EXPERT OPINION

IRAEs are unique compared to standard chemotherapy. As the role of ICIs expand across all stages of squamous cell NSCLC and with different combinations of antineoplastics, management of IRAEs will become crucial. Optimal management of IRAEs requires multidisciplinary teamwork. Further investigation into the pathophysiology of IRAEs can enhance current management strategies.

Liver Transplantation for Hepatocellular Carcinoma after Downstaging or Bridging Therapy with Immune Checkpoint Inhibitors

Liver transplantation offers excellent outcomes for patients with HCC. For those who initially present within the Milan criteria, bridging therapy is essential to control disease while awaiting liver transplant. For those who present beyond the Milan criteria, a liver transplant may still be considered following successful downstaging. Since the introduction of atezolizumab as part of the first-line treatment for HCC in 2020, there has been increasing interest in the use of ICIs as bridging or downstaging therapies prior to liver transplant. A total of six case reports/series have been published on this topic, with mixed outcomes. Overall, liver transplantation can be performed safely following prolonged ICI use, though ICIs may increase the risk of fulminant acute rejection early in the post-operative period. A minimal washout period between the last dose of ICI and liver transplantation has been identified as an important factor predicting transplant outcomes; however, further research is needed.

Immune checkpoint inhibitor-related hepatotoxicity: A review

The application of immune checkpoint inhibitors (ICI) in advanced cancer has been a major development in the last decade. The indications for ICIs are constantly expanding into new territory across different cancers, disease stages and lines of therapy. With this increased use, adverse events including immune checkpoint inhibitor-related hepatotoxicity (ICH) have emerged as an important clinical problem. This along with the introduction of ICI as first- and second-line treatments for advanced hepatocellular carcinoma makes ICH very relevant to gastroenterologists and hepatologists. The incidence of ICH varies between 1%-20% depending on the number, type and dose of ICI received. Investigation and management generally involve excluding differential diagnoses and following a stepwise escalation of withholding or ceasing ICI, corticosteroid treatment and adding other immunosuppressive agents depending on the severity of toxicity. The majority of patients with ICH recover and some may even safely recommence ICI therapy. Guideline recommendations are largely based on evidence derived from retrospective case series which highlights a priority for future research.

Atezolizumab and bevacizumab-induced encephalitis in advanced hepatocellular carcinoma: Case report and literature review

INTRODUCTION

On the basis of the results of the IMBRAVE-150 trial, the combination of atezolizumab, a programmed cell death ligand 1 (PD-L1) antibody, as well as bevacizumab, a vascular endothelial growth factor (VEGF) antibody, represents a promising novel first-line therapy in patients with advanced hepatocellular carcinoma (HCC). Despite favorable safety data, serious adverse events have been described. However, central nervous system complications such as encephalitis have rarely been reported. We present the case of a 70-year-old woman with hepatitis C virus (HCV)-related liver cirrhosis and advanced HCC who developed severe encephalitis after only one cycle of atezolizumab/bevacizumab.

PATIENT CONCERNS

Ten days after administration, the patient presented with confusion, somnolence, and emesis. Within a few days, the patient's condition deteriorated, and mechanical ventilation became necessary.

DIAGNOSIS

Cerebrospinal fluid (CSF) analysis showed increased cell count and elevated protein values. Further work-up revealed no signs of an infectious, paraneoplastic, or other autoimmune cause.

INTERVENTION

Suspecting an atezolizumab/bevacizumab-related encephalitis, we initiated a high-dose steroid pulse therapy as well as repeated plasmapheresis, which resulted in clinical improvement and remission of CSF abnormalities.

OUTCOME

Despite successful weaning and transfer to a rehabilitation ward, the patient died of progressive liver cancer 76 days after initial treatment with atezolizumab/bevacizumab, showing no response.

CONCLUSION

This case illustrates that rapid immunosuppressive treatment with prednisolone can result in remission even of severe encephalitis. We discuss this case in the context of available literature and previously reported cases of atezolizumab-induced encephalitis in different tumor entities, highlighting the diagnostic challenges in oncologic patients treated with immune checkpoint-inhibitors.

Molecular profiles of small cell lung cancer subtypes: therapeutic implications

Small cell lung cancer (SCLC; accounting for approximately 13%-15% of all lung cancers) is an exceptionally lethal malignancy characterized by rapid doubling time and high propensity to metastasize. In contrast to the increasingly personalized therapies in other types of lung cancer, SCLC is still regarded as a homogeneous disease and the prognosis of SCLC patients remains poor. Recently, however, substantial progress has been made in our understanding of SCLC biology. Advances in genomics and development of new preclinical models have facilitated insights into the intratumoral heterogeneity and specific genetic alterations of this disease. This worldwide resurgence of studies on SCLC has ultimately led to the development of novel subtype-specific classifications primarily based on the neuroendocrine features and distinct molecular profiles of SCLC. Importantly, these biologically distinct subtypes might define unique therapeutic vulnerabilities. Herein, we summarize the current knowledge on the molecular profiles of SCLC subtypes with a focus on their potential clinical implications.