PD-L1 Expression and Tumor-Infiltrating Lymphocytes in Thymic Epithelial Neoplasms

The Proteostasis of Thymic Stromal Cells in Health and Diseases

The thymus is the key immune organ for the development of T cells. Different populations of thymic stromal cells interact with T cells, thereby controlling the dynamic development of T cells through their differentiation and function. Proteostasis represents a balance between protein expression, folding, and modification and protein clearance, and its fluctuation usually depends at least partially on related protein regulatory systems for further survival and effects. However, in terms of the substantial requirement for self-antigens and their processing burden, increasing evidence highlights that protein regulation contributes to the physiological effects of thymic stromal cells. Impaired proteostasis may expedite the progression of thymic involution and dysfunction, accompanied by the development of autoimmune diseases or thymoma. Hence, in this review, we summarize the regulation of proteostasis within different types of thymic stromal cells under physiological and pathological conditions to identify potential targets for thymic regeneration and immunotherapy.

Immunotherapy in thymic epithelial tumors: tissue predictive biomarkers for immune checkpoint inhibitors

Thymic epithelial tumors (TETs) are rare malignant neoplasms arising in the thymus gland. Nevertheless, TETs, including thymomas (TMs), thymic carcinomas (TCs), and thymic neuroendocrine neoplasms (TNENs), are the most common mediastinal malignancies overall. A multidisciplinary approach is required for the appropriate diagnostic and therapeutic management of TETs. To date, the main therapeutic strategies are largely depended on the stage of the tumor and they include surgery with or without neoadjuvant or adjuvant therapy, represented by platinum-based chemotherapy, radiotherapy or chemoradiotherapy. Immune checkpoint inhibitors (ICIs) are ongoing under evaluation in the advanced or metastatic diseases despite the challenges related to the very low tumor mutation burden (TMB) and the high incidence of immune-related adverse events in TETs. In this regard, predictive impact of tissue biomarkers expression such as programmed cell death ligand-1 (PD-L1), and other emerging biomarkers, as well as their optimal and shared interpretation are currently under evaluation in order to predict response rates to ICIs in TETs.

Autoimmunity in thymic epithelial tumors: a not yet clarified pathologic paradigm associated with several unmet clinical needs

Thymic epithelial tumors (TETs) are rare mediastinal cancers originating from the thymus, classified in two main histotypes: thymoma and thymic carcinoma (TC). TETs affect a primary lymphoid organ playing a critical role in keeping T-cell homeostasis and ensuring an adequate immunological tolerance against "self". In particular, thymomas and not TC are frequently associated with autoimmune diseases (ADs), with Myasthenia Gravis being the most common AD present in 30% of patients with thymoma. This comorbidity, in addition to negatively affecting the quality and duration of patients' life, reduces the spectrum of the available therapeutic options. Indeed, the presence of autoimmunity represents an exclusion criteria for the administration of the newest immunotherapeutic treatments with checkpoint inhibitors. The pathophysiological correlation between TETs and autoimmunity remains a mystery. Several studies have demonstrated the presence of a residual and active thymopoiesis in adult patients affected by thymomas, especially in mixed and lymphocytic-rich thymomas, currently known as type AB and B thymomas. The aim of this review is to provide the state of art in regard to the histological features of the different TET histotype, to the role of the different immune cells infiltrating tumor microenvironments and their impact in the break of central immunologic thymic tolerance in thymomas. We discuss here both cellular and molecular immunologic mechanisms inducing the onset of autoimmunity in TETs, limiting the portfolio of therapeutic strategies against TETs and greatly impacting the prognosis of associated autoimmune diseases.

PD-L1 Expression in Neoplastic and Immune Cells of Thymic Epithelial Tumors: Correlations with Disease Characteristics and HDAC Expression

BACKGROUND

Programmed death-ligand 1 (PD-L1) expression in neoplastic and immune cells of the tumor microenvironment determines the efficacy of antitumor immunity, while it can be regulated at the epigenetic level by various factors, including HDACs. In this study, we aim to evaluate the expression patterns of PD-L1 in thymic epithelial tumors (TETs), while we attempt the first correlation analysis between PD-L1 and histone deacetylases (HDACs) expression.

METHODS

Immunohistochemistry was used to evaluate the expression of PD-L1 in tumor and immune cells of 91 TETs with SP263 and SP142 antibody clones, as well as the expressions of HDCA1, -2, -3, -4, -5, and -6.

RESULTS

The PD-L1 tumor proportion score (TPS) was higher, while the immune cell score (IC-score) was lower in the more aggressive TET subtypes and in more advanced Masaoka-Koga stages. A positive correlation between PD-L1 and HDAC-3, -4, and -5 cytoplasmic expression was identified.

CONCLUSIONS

Higher PD-L1 expression in neoplastic cells and lower PD-L1 expression in immune cells of TETs characterizes more aggressive and advanced neoplasms. Correlations between PD-L1 and HDAC expression unravel the impact of epigenetic regulation on the expression of immune checkpoint molecules in TETs, with possible future applications in combined therapeutic targeting.

Stage III-IV thymic squamous cell carcinoma in complete pathological remission achieved with thymic cancer resection after immunotherapy combined with chemotherapeutic conversion therapy: a report of two cases from real-world data

Background

Thymic carcinoma, a rare malignancy in the mediastinum, currently lacks standardized treatment options. Although surgery remains a crucial component among traditional therapeutic approaches, the potential benefits of radiotherapy and chemotherapy remain controversial. Nevertheless, a substantial number of patients are diagnosed with advanced tumor growth, posing challenges for achieving complete resection through surgical intervention and resulting in a poor prognosis. In light of the promising antitumor effects demonstrated by immunotherapy in various prevalent cancers, certain studies have shown favorable efficacy in advanced or recurrent thymic cancer cases. However, the incidence of adverse effects induced by immunotherapy in thymic cancer is notably higher compared to other tumor types, with severe and fatal complications being particularly significant. Consequently, there is an urgent need to address the crucial issue of patient selection for immunotherapy in thymic cancer.

Case Description

In this study, we report on the treatment with programmed cell death protein 1 (PD-1) inhibitor therapy combined with chemotherapy conversion therapy for two patients diagnosed with stage III-IV thymic squamous cell carcinoma according to the Masaoka-Koga staging system. The aim of this study was to assess the effectiveness and safety of PD-1 inhibitor combined with chemotherapy conversion therapy in patients with thymic squamous cell carcinoma. Two patients in this cohort, one with stage III and another with stage IV disease, were deemed ineligible for upfront surgical resection. Puncture pathology confirmed the diagnosis of thymic squamous cell carcinoma. Both patients underwent transformation therapy using a combination of PD-1 inhibitors and chemotherapy. Tumor shrinkage was observed in both patients, enabling successful completion of surgery. Postoperative pathology revealed no residual tumor cells, indicating complete pathological remission. Notably, none of the patients experienced grade 3 or higher immunotherapy-related adverse reactions following immunotherapy.

Conclusions

A combination of PD-1 inhibitors and chemotherapy followed by surgery demonstrated improved efficacy and enhanced safety for treating patients with Masaoka-Koga stage III-IV thymic squamous carcinoma and represents a potential novel therapeutic alternative for this disease.

Comprehensive study of clinicopathological and immune cell infiltration and lactate dehydrogenase expression in patients with thymic epithelial tumours

BACKGROUND

Lactate dehydrogenase (LDH) has emerged as a promising biomarker for cancer. However, the current understanding of LDH and circulating LDH expression in thymic epithelial tumour (TET) is lacking.

METHODS

A comprehensive literature review and meta-analysis were performed to evaluate the clinical significance of circulating LDH levels in patients with TET. Circulating LDH levels were measured using a laboratory analyser (Cobas8000, Roche, Basel, Switzerland). The maximum standardised uptake value (SUVmax) was determined in patients who underwent whole-body 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT). Multiplex immunohistochemistry (IHC) was performed using a commercially available kit (Opal 6-plex Detection Kit, Akoya Biosciences, Marlborough, MA, USA) and slide scanner (Slideview VS200, Olympus, Tokyo, Japan). All statistical analyses were performed using SPSS (IBM Corp., Armonk, NY, USA) and Prism version 9.0 (GraphPad Inc., San Diego, CA, USA). Differences with p < 0.05 were considered to be statistically significant.

RESULTS

Meta-analysis revealed that elevated circulating serum levels of LDH predicted poor prognosis in patients with TET. Circulating levels of LDH were analysed in the serum of 313 patients with TET and 87 with benign mediastinal mass. The mean circulating LDH level in patients with thymic carcinoma (TC) was significantly higher than that in those with thymoma (TM) and the benign group (p < 0.001). Expression levels of circulating LDH were significantly reduced in postoperative samples compared with that in preoperative samples (p < 0.05). Receiver operating characteristic (ROC) curve analysis for diagnosing TC yielded an area under the curve of 0.74, with a sensitivity of 54 % and specificity of 86 %. Furthermore, patients with TC exhibited higher 18F-FDG PET/CT SUVmax values compared to those with TM. Correlation analysis demonstrated a positive association between SUVmax values and circulating LDH levels. In addition, the percentages of LDH-positive cells in TC and type B1 TM tissues were higher than those in other subtypes of TM, and a significant positive correlation between the percentages of LDH-positive and CD20-positive cells was detected in patients with TET (p < 0.05).

CONCLUSION

Circulating serum LDH level may serve as a non-invasive biomarker for the diagnosis and prognosis of TET. The relationship between LDH expression and immune cell infiltration merits further regarding its application in companion diagnosis for immunotherapy.

Immunotherapy of thymic epithelial tumors: molecular understandings and clinical perspectives

Immunotherapy has emerged to play a rapidly expanding role in the treatment of cancers. Currently, many clinical trials of therapeutic agents are on ongoing with majority of immune checkpoint inhibitors (ICIs) especially programmed death receptor 1 (PD-1) and its ligand 1 (PD-L1) inhibitors. PD-1 and PD-L1, two main immune checkpoints, are expressed at high levels in thymic epithelial tumors (TETs) and could be predictors of the progression and immunotherapeutic efficacy of TETs. However, despite inspiring efficacy reported in clinical trials and clinical practice, significantly higher incidence of immune-related adverse events (irAEs) than other tumors bring challenges to the administration of ICIs in TETs. To develop safe and effective immunotherapeutic patterns in TETs, understanding the clinical properties of patients, the cellular and molecular mechanisms of immunotherapy and irAEs occurrence are crucial. In this review, the progress of both basic and clinical research on immune checkpoints in TETs, the evidence of therapeutic efficacy and irAEs based on PD-1 /PD-L1 inhibitors in TETs treatment are discussed. Additionally, we highlighted the possible mechanisms underlying irAEs, prevention and management strategies, the insufficiency of current research and some worthy research insights. High PD-1/PD-L1 expression in TETs provides a rationale for ICI use. Completed clinical trials have shown an encouraging efficacy of ICIs, despite the high rate of irAEs. A deeper mechanism understanding at molecular level how ICIs function in TETs and why irAEs occur will help maximize the immunotherapeutic efficacy while minimizing irAEs risks in TET treatment to improve patient prognosis.

The crosstalk between the gut microbiota and tumor immunity: Implications for cancer progression and treatment outcomes

The gastrointestinal tract is inhabited by trillions of commensal microorganisms that constitute the gut microbiota. As a main metabolic organ, the gut microbiota has co-evolved in a symbiotic relationship with its host, contributing to physiological homeostasis. Recent advances have provided mechanistic insights into the dual role of the gut microbiota in cancer pathogenesis. Particularly, compelling evidence indicates that the gut microbiota exerts regulatory effects on the host immune system to fight against cancer development. Some microbiota-derived metabolites have been suggested as potential activators of antitumor immunity. On the contrary, the disequilibrium of intestinal microbial communities, a condition termed dysbiosis, can induce cancer development. The altered gut microbiota reprograms the hostile tumor microenvironment (TME), thus allowing cancer cells to avoid immunosurvelliance. Furthermore, the gut microbiota has been associated with the effects and complications of cancer therapy given its prominent immunoregulatory properties. Therapeutic measures that aim to manipulate the interplay between the gut microbiota and tumor immunity may bring new breakthroughs in cancer treatment. Herein, we provide a comprehensive update on the evidence for the implication of the gut microbiota in immune-oncology and discuss the fundamental mechanisms underlying the influence of intestinal microbial communities on systemic cancer therapy, in order to provide important clues toward improving treatment outcomes in cancer patients.

Unraveling the Immune Microenvironment of Thymic Epithelial Tumors: Implications for Autoimmunity and Treatment

Thymic Epithelial Tumors (TETs) represent a rare tumor family, originating from the epithelial component of the thymus gland. Clinicopathologically, they are segregated into six major subtypes, associated with distinct histological features and clinical outcomes. Their emergence and evolution are accompanied by the generation of a complex tumor microenvironment (TME), dominated by phenotypically and functionally divergent immune cellular subsets, in different maturation states and in analogies that vary significantly among different subtypes. These heterogenous leukocyte populations exert either immune-permissive and tumor-suppressive functions or vice versa, and the dynamic equilibrium established among them either dictates the tumor immune milieu towards an immune-tolerance state or enables the development of a productive spontaneous tumoricidal response. The immunologically “hot” microenvironment, defining a significant proportion of TETs, makes them a promising candidate for the implementation of immune checkpoint inhibitors (ICIs). A number of phase I and II clinical trials have already demonstrated significant, type-specific clinical efficacy of PD-L1 inhibitors, even though substantial limitations in their utilization derive from their immune-mediated adverse effects. Moreover, the completed clinical studies involved relatively restricted patient samples and an expansion in the enrolled cohorts is required, so that more trustworthy conclusions regarding the benefit from ICIs in TETs can be extracted.

Characteristics of genomic mutations and signaling pathway alterations in thymic epithelial tumors

BACKGROUND

To elucidate the mechanisms of thymic epithelial tumor (TET) canceration by characterizing genomic mutations and signaling pathway alterations.

METHODS

Primary tumor and blood samples were collected from 21 patients diagnosed with TETs (thymoma and thymic cancer), 15 of whom were screened by nucleic acid extraction and whole exon sequencing. Bioinformatics was used to comprehensively analyze the sequencing data for these samples, including gene mutation information and the difference of tumor mutation burden (TMB) between thymoma and thymic carcinoma groups. We performed signaling pathway and functional enrichment analysis using the WebGestalt 2017 toolkit.

RESULTS

ZNF429 (36%) was the gene with the highest mutation frequency in thymic carcinoma. Mutations in BAP1 (14%), ABI1 (7%), BCL9L (7%), and CHEK2 (7%) were exclusively detected in thymic carcinoma, whereas ZNF721 mutations (14%) and PABPC1 (14%) were found exclusively in thymoma. The mean TMB values for thymic carcinoma and thymoma were 0.722 and 0.663 mutations per megabase (Mb), respectively, and these differences were not statistically significant. The ErbB signaling pathway was enriched in the thymoma and intersection groups, and pathways of central carbon metabolism in cancer, longevity regulating and MAPK signaling were only found in the thymoma group, while pathways in cancer (hsa05200) was found in the thymoma and thymic carcinoma groups.

CONCLUSIONS

Multiple differences in somatic genes and pathways have been identified. Our findings provide insights into differences between thymoma and thymic carcinoma that could aid in designing personalized clinical therapeutic strategies.

The efficacy and safety of immunotherapy in thymic epithelial tumors: more effective, more risky: a systematic review

Background

Thymic epithelial tumors (TETs) are rare malignant neoplasms originating from thymic epithelial cells. The current treatment for localized TETs is surgical removal. However, 20-30% of thymomas and 70-80% of thymic carcinomas are unresectable, recurrent, or metastatic at the time of detection. The standard therapy for these patients is chemotherapy, but the effect is limited. With a deeper understanding of tumor immunity, immunotherapy for various cancers has rapidly developed. Antibodies against cytotoxic T-lymphocyte antigen-4, programmed death-1, and programmed death-ligand 1 have been approved for the treatment of many solid tumors. Compared with traditional treatments, these immune checkpoint inhibitors (ICIs) have better efficacy and lower toxicity. Recently, ICIs have been used more enthusiastically in the treatment of TETs. However, due to the unique biological characteristics of the thymus, immunotherapy usually causes severe immune-related adverse events (irAEs). Most previous studies on immunotherapy in TETs had small sample sizes and reported diverse conclusions.

Methods

We collected relevant studies in PubMed during the last five years and analyzed the available data to discuss the efficacy and safety of ICIs in TETs.

Results

According to 14 previous studies in the past five years, all TETs showed expression of programmed death-ligand 1, while thymic carcinomas showed 100% expression. The best median progression-free survival (mPFS) among the five studies was 6.5 months, and the best median overall survival (mOS) was 24.9 months. In addition, the most common irAEs were myasthenic symptoms, liver enzyme elevation, and elevated creatine phosphokinase levels.

Conclusions

ICIs can be used in TET treatment, especially for thymic carcinomas, in the absence of standard second-line treatment. However, more attention should be paid to irAEs.

Induction Strategy for Locally Advanced Thymoma

Surgery remains cornerstone for the management of thymoma. Complete surgical resection (R0), is recognized as the constant and significant factor for prognosis. However, in locally advanced (Masaoka-Koga stages III-IVa) thymomas, achieving R0 resection remains challenging due to local-regional invasion of the disease. Induction treatment, with the aim of reducing bulky tumor mass, offers new strategy to facilitate totally surgical resection. Herein, we reviewed recent progress and provided a comprehensive overview of induction strategy in locally advance thymoma.

The Expression of PD-L1 and B7-H4 in Thymic Epithelial Tumor and Its Relationship With Tumor Immune-Infiltrating Cells

Background

PD-L1 and B7-H4 have been reported to be expressed in various malignancies and are considered as promising prognostic factors and potential immunotherapy targets.

Methods

We analyzed the correlation between the expression of PD-L1 and B7-H4 transcriptomes and clinicopathological characteristics in 121 TET patients from The Cancer Genome Atlas (TCGA) database. The immune-infiltration levels in the TET microenvironment were estimated using ssGSEA and quanTiseq algorithms. We collected 80 TET cases from 2008 to 2015. PD-L1、B7-H4、FOXP3 and CD163 protein expression in tumor tissues were detected by immunohistochemistry.

Results

TCGA database showed PD-L1 mRNA levels can predict the OS (P = 0.018) and DFS (P = 0.033) of TET patients. B7-H4 mRNA levels were positively related to the World Health Organization (WHO) pathological classification (P = 0.003) but not correlated with patient prognosis. Immune infiltration analysis showed PD-L1 is positively correlated with Tregs and M2 macrophages, B7-H4 is positively correlated with Tregs. Patients with high PD-L1 and Tregs or M2 macrophages, high B7-H4 and Tregs had a worse prognosis. Immunohistochemistry showed PD-L1 expression was positively correlated with the WHO pathological classification and Masaoka stage (P = 0.025, 0.003) and high PD-L1 expression can predict the poor OS of patients (P = 0.043); B7-H4 was also positively correlated with WHO pathological classification and Masaoka stage (P = 0.036, 0.049). However, B7-H4 expression did not correlate with patient prognosis. Evaluation of co-expression patterns showed TET patients with a high-grade WHO pathological classification harbored a 44.4% co-expression of PD-L1 and B7-H4. In addition, we found the expression level of PD-L1 is positively correlated with FOXP3 and CD163 (P = 0.004, P = 0.029) and B7-H4 is positively correlated with FOXP3 (P = 0.037). High PD-L1 combined with High FOXP3 and High CD163, High B7-H4 combined with High FOXP3 can be used to predict the poor prognosis of TET patients (P = 0.026, 0.031, 0.028, respectively).

Conclusion

PD-L1 and B7-H4 were related to the aggressiveness of TET and their expression level can indicate the suppressive immune microenvironment. Combined with FOXP3 and CD163, PD-L1 and B7-H4 can indicate a poor prognosis of TET.

Narrative review of immunotherapy in thymic malignancies

Thymomas and thymic carcinomas (TCs) (also known as Thymic Epithelial Tumors or TETs) are rare cancers and the most frequent masses of the anterior mediastinum. These tumors appear in the epithelial component of the thymus, a primary lymphoid organ, and they have reported a high risk of auto-immunity due to a unique biology. Indeed, up to 30% of patients with TETs could present an autoimmune disorder (AID), the most frequent being Myasthenia Gravis (MG). Moreover, AIDs have been reported not only at tumor diagnosis but before and during the follow-up. These tumors have a lack of specific therapeutic targets for metastatic setting. Immune checkpoint inhibitors (ICI) may defeat cancer cells' capacity to evade the immune system and proliferate. The long-term benefit of ICIs in the metastatic setting in several tumors, such as melanoma or non-small cell lung cancer (NSCLC), let to evaluate ICI approaches in TETs. The high rate of AIDs and distribution of autoimmune events among TET's histological subtypes may have an influence on the decision regarding a treatment based on ICI due to the increased risk of toxicity. We summarize the current evidence for the efficacy of ICI in thymoma and TC and discuss several unresolved challenges and concerns for the use of this agents in TETs.

Difference in the distribution of tumor-infiltrating CD8+ T cells and FOXP3+ T cells between micronodular thymoma with lymphoid stroma and micronodular thymic carcinoma with lymphoid stroma

Micronodular thymoma with lymphoid stroma (MNT) is a rare thymic epithelial neoplasm subtype characterized by a micronodular tumor cell growth pattern and abundant lymphoid stroma. Micronodular thymic carcinoma with lymphoid stroma (MNCA) is considered as a malignant counterpart of MNT and exhibits a growth pattern similar to that of MNT but has histologic features reminiscent of thymic squamous cell carcinoma, such as cytologic atypia and CD5 and CD117 immunoexpression. Although both MNT and MNCA are characterized by abundant lymphoid stroma, it remains unknown whether there are differences in infiltrating lymphocytes between MNT and MNCA. We analyzed the immune microenvironment profile in eight MNT and three MNCA cases. The cell density of CD8‐positive T cells was significantly higher in MNT than in MNCA, whereas that of FOXP3‐positive T cells was significantly higher in MNCA than in MNT. There was no significant difference in the cell density of programmed death protein 1‐positive T cells and programmed death ligand 1 expression between the MNT and MNCA cases. Our findings indicated that the immune microenvironment of MNCA differed from that of MNT and, compared with the T‐cell profile of MNT, that of MNCA was more suppressive to patients′ antitumor immune response.

Immunotherapy for thymoma

Thymic epithelial tumors (TETs) are rare thymic neoplasms. There are approximately 1.5 cases per million TETs per year. They are the most common anterior mediastinal tumors in adults. Due to limited activity of available treatment options novel strategies and treatment options are needed and treatment with immune checkpoint inhibitors is an attractive option. Thymic epithelial tumors have one of the lowest tumor mutational burden among all cancer in adults, but high expression of PD-L1 on tumor cells and abundant CD8+ lymphocytes provide a strong rational for implementing immune checkpoint inhibitors (ICIs) which target PD-1/PD-L1 pathway in the treatment of TETs. Few small early stage clinical trials were published so far evaluating efficacy of pembrolizumab and avelumab in thymoma and thymic carcinoma patients. Al trials showed reasonable response rates and progression-free survival. Higher PD-L1 expression was predictor of response in all trials. However, increased incidence of immune-related adverse events was seen in TET patients treated with immune checkpoint inhibitors compared to patients with other cancers. At the moment, ICIs are not standard of care for patients with TET and larger trials are needed to establish the right role of ICIs regarding efficacy and safety of these agents.

Nivolumab treatment for metastatic thymic epithelial tumors

BACKGROUND

Metastatic and unresectable thymoma (T) or thymic carcinoma (TC) have limited treatment options, especially after first line.

METHODS

Patients with unresectable or recurrent thymic tumors who used minimum one dose of nivolumab at any line of treatment were evaluated retrospectively. Even though nivolumab was administered 3mg/kg dosage in PRIMER study, due to toxicity and financial concerns, we used low dose regimen mostly.

RESULTS

Among 46 unresectable and recurrent thymic epithelial tumors; 8 patients with TC (n = 3), T (n = 4) and mixt histology (n = 1) were reviewed. Three patients had myasthenia gravis history that had to be controlled before treatment. Four patients showed moderate (n = 2) or severe (n = 2) adverse events with nivolumab treatment. Interestingly, two severe adverse events were occurred at first dose even with 40 mg nivolumab and required cessation of treatment permanently. The median number of nivolumab received was four (range: 1-18). Best response was partial response. Two patients progressed at the 3rd and 5th month of treatment. Best duration of response for one patient with TC and one patient with T-B2 were 9 and 14 months, respectively. Median survival time after nivolumab was 7.4 months (range: 2-22.1).

CONCLUSIONS

After the results of the previous study could be supported by randomized prospective studies with more number of patients, nivolumab may be considered as an option in patients with thymic epithelial tumors who have received multiple line treatments. However, given the high rate of severe toxicities, there is need to find out a reliable marker to prediction patients who will derive benefit or exhibit toxicity.

Primary Driver Mutations in GTF2I Specific to the Development of Thymomas

Thymomas are rare mediastinal tumors that are difficult to treat and pose a major public health concern. Identifying mutations in target genes is vital for the development of novel therapeutic strategies. Type A thymomas possess a missense mutation in GTF2I (chromosome 7 c.74146970T>A) with high frequency. However, the molecular pathways underlying the tumorigenesis of other thymomas remain to be elucidated. We aimed to detect this missense mutation in GTF2I in other thymoma subtypes (types B). This study involved 22 patients who underwent surgery for thymomas between January 2014 and August 2019. We isolated tumor cells from formalin-fixed paraffin-embedded tissues from the primary lesions using laser-capture microdissection. Subsequently, we performed targeted sequencing to detect mutant GTF2I coupled with molecular barcoding. We used PyClone analysis to determine the fraction of tumor cells harboring mutant GTF2I. We detected the missense mutation (chromosome 7 c.74146970T>A) in GTF2I in 14 thymomas among the 22 samples (64%). This mutation was harbored in many type B thymomas as well as type A and AB thymomas. The allele fraction for the tumors containing the mutations was variable, primarily owing to the coexistence of normal lymphocytes in the tumors, especially in type B thymomas. PyClone analysis revealed a high cellular prevalence of mutant GTF2I in tumor cells. Mutant GTF2I was not detected in other carcinomas (lung, gastric, colorectal, or hepatocellular carcinoma) or lymphomas. In conclusion, the majority of thymomas harbor mutations in GTF2I that can be potentially used as a novel therapeutic target in patients with thymomas.

Patient-Derived Tumor Xenograft Models: Toward the Establishment of Precision Cancer Medicine

Patient-derived xenografts (PDXs) describe models involving the implantation of patient-derived tumor tissue into immunodeficient mice. Compared with conventional preclinical models involving the implantation of cancer cell lines into mice, PDXs can be characterized by the preservation of tumor heterogeneity, and the tumor microenvironment (including stroma/vasculature) more closely resembles that in patients. Consequently, the use of PDX models has improved the predictability of clinical therapeutic responses to 80% or greater, compared with approximately 5% for existing models. In the future, molecular biological analyses, omics analyses, and other experiments will be conducted using recently prepared PDX models under the strong expectation that the analysis of cancer pathophysiology, stem cells, and novel treatment targets and biomarkers will be improved, thereby promoting drug development. This review outlines the methods for preparing PDX models, advances in cancer research using PDX mice, and perspectives for the establishment of precision cancer medicine within the framework of personalized cancer medicine.

Airway Microbiota as a Modulator of Lung Cancer

Recent research on cancer-associated microbial communities has elucidated the interplay between bacteria, immune cells, and tumor cells; the bacterial pathways involved in the induction of carcinogenesis; and their clinical significance. Although accumulating evidence shows that a dysbiotic condition is associated with lung carcinogenesis, the underlying mechanisms remain unclear. Microorganisms possibly trigger tumor initiation and progression, presumably via the production of bacterial toxins and other pro-inflammatory factors. The purpose of this review is to discuss the basic role of the airway microbiome in carcinogenesis and the underlying molecular mechanisms, with the aim of developing anticancer strategies involving the airway microbiota. In addition, the mechanisms via which the microbiome acts as a modulator of immunotherapies in lung cancer are summarized.

Immunosurveillance and Immunoediting of Lung Cancer: Current Perspectives and Challenges

The immune system plays a dual role in tumor evolution-it can identify and control nascent tumor cells in a process called immunosurveillance and can promote tumor progression through immunosuppression via various mechanisms. Thus, bilateral host-protective and tumor-promoting actions of immunity are integrated as cancer immunoediting. In this decade, immune checkpoint inhibitors, specifically programmed cell death 1 (PD-1) pathway inhibitors, have changed the treatment paradigm of advanced non-small cell lung cancer (NSCLC). These agents are approved for the treatment of patients with NSCLC and demonstrate impressive clinical activity and durable responses in some patients. However, for many NSCLC patients, the efficacy of immune checkpoint inhibitors is limited. To optimize the full utility of the immune system for eradicating cancer, a broader understanding of cancer immunosurveillance and immunoediting is essential. In this review, we discuss the fundamental knowledge of the phenomena and provide an overview of the next-generation immunotherapies in the pipeline.