Prognostic Value of Programmed Death Ligand 1 and Programmed Death 1 Expression in Thymic Carcinoma

Peripheral blood PD-1+ T lymphocytes as biomarkers in liquid biopsies for solid tumors: Clinical significance and prognostic applications

A shift toward a T cell exhaustion phenotype is associated with the upregulation of expression of programmed cell death protein 1 (PD-1) on T lymphocytes in patients with malignant solid tumors. The interaction between PD-1 and programmed death-ligand 1 (PD-L1) inhibits PD-1+ T lymphocyte function, impacting their anti-tumor immune activity. Immune checkpoint inhibitors targeting PD-1/PD-L1 have revolutionized the treatment of various solid malignancies, improving therapeutic efficacy and survival outcomes. Peripheral blood analysis of liquid biopsies is being increasingly used to identify populations most likely to benefit from various treatment modalities. PD-1+ T lymphocytes represent the primary cell population responsive to immunotherapeutic interventions for patients with solid malignancies, as evidenced by the altered PD-1 expression levels and proportion of cells comprising the overall population of immunocytes. PD-1+ T cells in peripheral blood exert an associative and reciprocal predictive effect on homologous intratumoral cells. Distinct subpopulations of PD-1+ T cells exhibit differential ability to proliferate in the periphery and can be characterized by tumor antigen-specific and exhaustion phenotypes. These characteristics have prognostic implications, aiding in the prediction of the efficacy of antitumor therapy and predicting survival outcomes. We highlight distinct subpopulations of PD-1+ T cells, their exhaustion and antigen-specific phenotypes, and their dynamic changes over treatment, providing insights into their utility for tailoring personalized therapies. For the first time, this review discusses the role of peripheral PD-1+ T lymphocytes as prognostic biomarkers in liquid biopsies, focusing on their clinical significance, predictive value during therapy, and future research directions.

Thymic epithelial tumor medical treatment: A narrative review

Thymic epithelial tumors, a malignancy originating in the thymus, are the commonest primary neoplasm of the anterior mediastinum; however, among thoracic tumors, they have a relatively low incidence rare. Thymic epithelial tumors can be broadly classified into thymic carcinoma and thymoma. As the cornerstone of thymic tumor treatment, surgery is the preferred treatment for early-stage patients, whereas, for advanced unresectable thymic tumors, the treatment is chemoradiotherapy. Targeted therapy is less effective for thymic tumors. Moreover, the use of immune checkpoint inhibitors as another effective treatment option for advanced unresectable thymic tumors, particularly thymomas, is limited owing to immune-related adverse effects. Here, we have summarized all pertinent information regarding chemotherapy, especially preoperative neoadjuvant chemotherapy, and chemotherapy in combination with other treatments, and reviewed the effectiveness of these procedures and recent advances in targeted therapy. In addition, we analyzed the efficacy and safety of immune checkpoint inhibitors in thymic epithelial tumors, to provide a holistic treatment view.

The influence of PD-L1 expression levels on the efficacy of combination therapy in thymic epithelial tumors

BACKGROUND

The significant expression of PD-L1 in thymic epithelial tumors (TETs) has been confirmed, and immunotherapy and its combination therapy have been effective in TETs. However, there is no present evidence that the expression levels of PD-L1 affects the efficacy of combination therapy. Our study aimed to shed light on this relationship.

METHODS

Patients with thymic epithelial tumors (TETs) from multicenter hospitals were retrospectively identified. Objective response rate (ORR), progression-free survival (PFS), overall survival (OS), and immune-related adverse events (irAEs) in 22 patients were included. We divided the patients the 22 patients with PD-L1 test into three levels (high expression, low expression and no expression) and analyzed the relationship between the levels of PD-L1 expression and the efficacy of combination therapy.

RESULTS

Combination therapy showed an effective benefit in 22 patients with TETs, the median PFS (mPFS) was 16 months (95% CI: 8.5-23.5) and the median OS (mOS) was 38 months (95% CI: 21.5-54.5). Cox-regressive analysis found whether PD-L1 expression affected the PFS of patients (p = 0.017). Among the patients with PD-L1 expression, the levels of expression were correlated with curative effect (Kruskal-Wallis test, PFS: P = 0.012; OS: P = 0.01), and high expression group was along with better efficacy than low expression (Wilcoxon test, P = 0.01). Moreover, in 17 patients treated with immunotherapy combined with chemotherapy, the expression of PD-L1 was also associated with efficacy (Kruskal-Wallis test, p = 0.021).

CONCLUSIONS

PD-L1 expression affects the PFS of patients. High expression of PD-L1 patients with TETs responded better to combination therapy, which could provide a therapeutic option in clinic. Besides, other targeted treatments should be considered.

Case report: A sustained survival benefit of third-line immunotherapy for refractory thymic carcinoma

Thymic carcinoma (TC) is an uncommon type of thymic epithelial tumors. Patients with relapsed or refractory TCs have a poor prognosis. Immune checkpoint inhibitor monotherapy can be applied as a second-line treatment for such cases. This study reported a TC patient who did not respond to conventional chemotherapy and radiotherapy but achieved prolonged partial remission lasting 17 months following the third-line treatment with anti-programmed cell death-1 inhibitor sintilimab. This patient did not experience any serious side effects associated with sintilimab treatment. The above results demonstrated that sintilimab could be a feasible therapeutic option for refractory TC patients.

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.

Molecular and Functional Key Features and Oncogenic Drivers in Thymic Carcinomas

Thymic epithelial tumors, comprising thymic carcinomas and thymomas, are rare neoplasms. They differ in histology, prognosis, and association with autoimmune diseases such as myasthenia gravis. Thymomas, but not thymic carcinomas, often harbor GTF2I mutations. Mutations of CDKN2A, TP53, and CDKN2B are the most common thymic carcinomas. The acquisition of mutations in genes that control chromatin modifications and epigenetic regulation occurs in the advanced stages of thymic carcinomas. Anti-angiogenic drugs and immune checkpoint inhibitors targeting the PD-1/PD-L1 axis have shown promising results for the treatment of unresectable tumors. Since thymic carcinomas are frankly aggressive tumors, this report presents insights into their oncogenic drivers, categorized under the established hallmarks of cancer.

Immunotherapy and Targeted Therapies Efficacy in Thymic Epithelial Tumors: A Systematic Review

BACKGROUND

Thymic epithelial tumors (TET) are rare neoplasms of the anterior mediastinum. Surgery is the mainstay treatment for resectable TET, whereas systemic treatments are reserved for unresectable and metastatic tumors. The development of new treatments, such as immune checkpoint inhibitors (ICI) and targeted therapies, with promising results in other types of solid tumors, has led to the investigation of their potential efficacy in TET. The study of tumor microenvironments (TME) is another field of investigation that has gained the interest of researchers. Taking into account the complex structure of the thymus and its function in the development of immunity, researchers have focused on TME elements that could predict ICI efficacy.

MATERIALS AND METHODS

The primary objective of this systematic review was to investigate the efficacy of ICI in TET. Secondary objectives included the toxicity of ICI, the efficacy of targeted therapies in TET, and the evaluation of the elements of TME that may be predictive factors of ICI efficacy. A literature search was conducted in February 2023 using the Ovid Medline and SciVerse Scopus databases.

RESULTS

2944 abstracts were retrieved, of which 31 were retained for the systematic review. Five phase II and one retrospective study assessed ICI efficacy. The overall response rate (ORR) varied from 0% to 34%. Median progression-free survival (PFS) ranged from 3.8 to 8.6 months, being lower in thymic carcinoma (TC) (3.8-4.2 months). Median overall survival (OS) ranged from 14.1 to 35.4 months. Treatment-related adverse events occurred in 6.6% to 27.3% of patients. Sixteen studies assessed targeted therapies. The most active molecule was lenvatinib, with 38% ORR in patients with TC while no activity was detected for imatinib, erlotinib plus bevacizumab, and saracatinib. Ten studies assessed TME elements that could predict ICI efficacy. Four studies focused on the tumor-infiltrating immune cells suggesting improved outcomes in patients with TC and high tumor-infiltrating lymphocyte densities. Another study showed that CD8+, CD20+, and CD204+ tumor-infiltrating immune cells in cancer stroma might be prognostic biomarkers in TC. Another study identified the immune-related long non-coding RNAs as a predictor of response to ICI. Tumor mutational burden was identified as a predictive factor of ICI efficacy in one study.

CONCLUSIONS

Despite study heterogeneity, this review shows that ICI could be a therapeutic option for selected patients with TET that are not amenable to curative radical treatment after first-line chemotherapy.

Unraveling molecular networks in thymic epithelial tumors: deciphering the unique signatures

Thymic epithelial tumors (TETs) are a rare and diverse group of neoplasms characterized by distinct molecular signatures. This review delves into the complex molecular networks of TETs, highlighting key aspects such as chromosomal abnormalities, molecular subtypes, aberrant gene mutations and expressions, structural gene rearrangements, and epigenetic changes. Additionally, the influence of the dynamic tumor microenvironment on TET behavior and therapeutic responses is examined. A thorough understanding of these facets elucidates TET pathogenesis, offering avenues for enhancing diagnostic accuracy, refining prognostic assessments, and tailoring targeted therapeutic strategies. Our review underscores the importance of deciphering TETs' unique molecular signatures to advance personalized treatment paradigms and improve patient outcomes. We also discuss future research directions and anticipated challenges in this intriguing field.

Emerging therapies in thymic epithelial tumors (Review)

Thymic epithelial tumors (TETs), including thymomas and thymic carcinomas, are rare malignancies arising from the thymus gland. The optimal management requires a multidisciplinary approach. Standard first-line systemic treatment involves cytotoxic chemotherapeutic regimens; however, alternative options for systemic treatment are required. Current research focuses on the unique profile of immune-related pathogenic mechanisms of TETs, involving an overlap with certain autoimmune phenotypes, as well as on determining the landscape of oncogenic molecular alterations and the role of tumor angiogenesis. The aim of the present review is to summarize the current clinical investigation on immunotherapy and targeted agents in the management of TETs. Regarding immune checkpoint inhibitors, efficacy results are promising in certain subsets of patients; however, caution is required concerning their toxicity. Anti-angiogenic agents, mainly potent small-molecule inhibitors, have demonstrated antitumor activity in TETs, whereas other targeted agents, including KIT inhibitors and epigenetic agents, are associated with encouraging, yet still modest results for unselected populations, in the absence of predictive biomarkers. Future research should focus on identifying predictive biomarkers for patients with TETs, and should implement multicenter collaborations and appropriate clinical trials tailored for rare tumor types.

Tumor Microenvironment in Thymic Epithelial Tumors: A Narrative Review

The tumor microenvironment (TME) is a complex and constantly changing entity. The TME consists of stromal cells, fibroblasts, endothelial cells, and innate and adaptive immune cells. Cancer development and progression occurs through this interplay between the tumor and the adjacent stroma. Cancer cells are capable of modifying their microenvironment by secreting various message-carrying molecules, such as cytokines, chemokines, and other factors. This action causes a reprogramming of the neighboring cells, which are enabled to play a crucial role in tumor survival and progression. The study of TME has many clinical implications in terms of cancer therapeutics because many new drugs, such as antibodies, kinase inhibitors, and liposome formulations that can encapsulate anti-cancer drugs, can be developed. Although chemotherapy is considered the standard of treatment for advanced disease, recent research has brought to light immunotherapy as a possible systemic alternative. However, the complex structure and function of the thymus hinders its routine use in clinical practice. The aim of this review paper is to discuss the recent advances in the investigation of the unique characteristics of the TME of thymic epithelial tumors that could possibly lead to the development of novel promising therapies.

Fatal toxicity induced by anti-PD-1 immune checkpoint inhibitor in thymic epithelial tumor

A standard treatment for advanced thymic epithelial tumors (TETs) after initial treatment remains unavailable to date. Targeted immune checkpoint inhibitors (ICIs) of the programmed cell death-1 (PD-1) pathway may produce objective responses in TETs, notably thymic carcinoma. Findings of clinical trials suggested ICIs are a practical choice. However, the risk of severe immuno-related adverse events is higher in TETs. Concerning histologic subtypes, thymomas are more frequently associated with autoimmune disorders than carcinomas, so close monitoring is needed for thymomas. In this article, we describe four cases of fatal toxicity caused by anti-PD-1 therapy in TETs. Four patients with metastatic thymomas or carcinoma difficult to treat with first-line standard chemotherapy were treated with the anti-PD-1 drug pembrolizumab or sintilimab. The association of PD-1 inhibitors with a high proportion of severe immuno-related adverse events in TETs necessitates attentive monitoring during treatment.

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.

Tumour immune microenvironment in resected thymic carcinomas as a predictor of clinical outcome

BACKGROUND

The spatial distribution of tumour-infiltrating lymphocytes (TILs) is a novel descriptor characterising the tumour immune microenvironment (TIME). The aim of our study was to assess whether a specific TIME of surgically resected thymic carcinoma (TC) can predict tumour invasiveness, recurrence or survival.

METHODS

Digital microscopy was performed on 39 TCs immunohistochemically stained to investigate the activation of the immune checkpoint pathway (PD-L1/PD-1), along with density and spatial distribution of TILs phenotypes (CD3+, CD4+, CD8+, FOXP3+, CD56+). The impact of PD-L1 and TIL density considering the intratumoural (iTILs) and stromal (sTILs) distribution on pathological characteristics and clinical outcomes were analysed.

RESULTS

In early TC stages, we observed a higher total density of CD3+ (p = 0.05) and CD8+ (p = 0.02) TILs. PD-L1 was expressed in 71.8% of TCs. In advanced TC stages, we observed a lower density of CD3+ (p = 0.04) and CD8+ (p = 0.01) iTILs compared to early stages. Serum concentrations of PD-L1 were significantly higher in TCs compared to healthy controls: 134.43 ± 18.51 vs. 82.01 ± 6.34 pg/ml (p = 0.001), respectively. High densities of stromal CD4+ TILs (54 vs. 32%, p = 0.043) and CD8+ TILs (65 vs. 17%, p = 0.048) were associated with improved freedom from recurrence (FFR) and cause-specific survival (CSS). High density of FoxP3+ TILs were associated with improved FFR (p = 0.03) and CSS (p = 0.003).

DISCUSSION

Mapping TIL subpopulations complement the armamentarium for prognostication of TC outcomes. The improved outcome in patients with high density of TILs supports the use of immune checkpoint inhibitors in TC patients.

PD-L1 Protein Expression Is Associated With Good Clinical Outcomes and Nomogram for Prediction of Disease Free Survival and Overall Survival in Breast Cancer Patients Received Neoadjuvant Chemotherapy

Objective

This study aims to investigate the potential prognostic significance of programmed death ligand-1 (PD-L1) protein expression in tumor cells of breast cancer patients received neoadjuvant chemotherapy (NACT).

Methods

Using semiquantitative immunohistochemistry, the PD-L1 protein expression in breast cancer tissues was analyzed. The correlations between PD-L1 protein expression and clinicopathologic characteristics were analyzed using Chi-square test or Fisher’s exact test. The survival curve was stemmed from Kaplan-Meier assay, and the log-rank test was used to compare survival distributions against individual index levels. Univariate and multivariate Cox proportional hazards regression models were accessed to analyze the associations between PD-L1 protein expression and survival outcomes. A predictive nomogram model was constructed in accordance with the results of multivariate Cox model. Calibration analyses and decision curve analyses (DCA) were performed for the calibration of the nomogram model, and subsequently adopted to assess the accuracy and benefits of the nomogram model.

Results

A total of 104 breast cancer patients received NACT were enrolled into this study. According to semiquantitative scoring for IHC, patients were divided into: low PD-L1 group (61 cases) and high PD-L1 group (43 cases). Patients with high PD-L1 protein expression were associated with longer disease free survival (DFS) (mean: 48.21 months vs. 31.16 months; P=0.011) and overall survival (OS) (mean: 83.18 months vs. 63.31 months; P=0.019) than those with low PD-L1 protein expression. Univariate and multivariate analyses indicated that PD-L1, duration of neoadjuvant therapy, E-Cadherin, targeted therapy were the independent prognostic factors for patients’ DFS and OS. Nomogram based on these independent prognostic factors was used to evaluate the DFS and OS time. The calibration plots shown PD-L1 based nomogram predictions were basically consistent with actual observations for assessments of 1-, 3-, and 5-year DFS and OS time. The DCA curves indicated the PD-L1 based nomogram had better predictive clinical applications regarding prognostic assessments of 3- and 5-year DFS and OS, respectively.

Conclusion

High PD-L1 protein expression was associated with significantly better prognoses and longer DFS and OS in breast cancer patients. Furthermore, PD-L1 protein expression was found to be a significant prognostic factor for patients who received NACT.

Clinicopathological analysis of immunohistochemical expression of immune checkpoint molecules in follicular lymphoma

Follicular lymphoma (FL) is characterized by an indolent clinical course and a high relapse rate, and often exhibits a diffuse pattern beyond the follicular area. Our group previously reported that immune checkpoint (ICP) pathways, such as programmed cell death (PD-1) and programmed death ligand 1 (PD-L1), are poor prognostic factors for diffuse large B-cell lymphoma and adult T-cell leukemia/lymphoma.In this study, the association between the expression of multiple ICP molecules according to immunohistochemistry and clinicopathological features in FL was determined via immunostaining of 173 biopsy samples. Membrane and/or cytoplasm expression of CD86 (nCD86) and PD-L1 (nPD-L1) was found in tumor cells, whereas PD-1 (miPD-1), Galectin-9 (miGalectin-9), OX40 (miOX40), CTLA-4 (miCTLA-4), Tim-3 (miTim-3), OX40L (miOX40L), and LAG-3 (miLAG-3) were expressed in non-neoplastic stromal cells. MiPD-1 expression was significantly higher in the follicular area than in the diffuse area (p=0.0450). Expression of miOX40 and miCTLA-4 was significantly higher in the diffuse area than in the follicular area (respectively, p=0.0053 and p=0.0092). MiTim-3 tended to be higher in the diffuse area than in the follicular area (p=0.0616). MiTim-3 was significantly higher in relapse cases than in new-onset cases (p=0.0440); miLAG-3 tended to be higher in relapse cases than in new-onset cases (p=0.0622, not significant). The miOX40L-high FL group had a significantly worse overall survival than the miOX40L-low group (p=0.0320).The expression of multiple ICP molecules on several cells reflects activated anti-tumor immunity and the unique FL microenvironment. Further studies on gene expression or genomic abnormalities will reveal the clinical and biological significance of ICP molecules in FL. This article is protected by copyright. All rights reserved.

CD70 in Thymic Squamous Cell Carcinoma: Potential Diagnostic Markers and Immunotherapeutic Targets

CD70 – a ligand protein of CD27 on lymphocytes – is expressed in a large spectrum of malignancies. It is an attractive target for antibody-based therapy and several clinical trials are currently being conducted. However, there is no evidence regarding the expression of CD70 and its relationship with expression of programmed death ligand-1 (PD-L1) and CD27+ tumor-infiltrating lymphocytes (TIL) in formalin-fixed paraffin-embedded (FFPE) tissues of thymic tumors. FFPE tissues of thymic squamous cell carcinoma (TSCC) (operative specimens, n = 31; biopsy specimens, n = 11), thymoma (n = 60), thymic carcinoid (n = 3), and lung squamous cell carcinoma (LSCC) (n = 30) were analyzed immunohistochemically. Immunoreactivity for CD70 was semi-quantitatively scored according to the proportion of positive tumor cells. Moreover, the densities of CD27-positive intratumoral TIL (iTIL) and stromal TIL of TSCC were assessed and survival was compared. Most TSCC cases (87%; 27/31) were CD70-positive. In contrast, all thymoma and thymic carcinoid cases were CD70-negative. In LSCC cases, CD70-positivity was significantly lower than TSCC cases (20%; 6/30). Biopsy and resected specimens obtained from the same patients demonstrated a consistent staining pattern (6/6 patients). The proportion of CD70-positive TSCC was comparable with those of CD5 (87%) and CD117 (90%). Correlation between CD70 and PD-L1 expression score was observed. There was no significant difference in survival between the CD70-high and CD70-low expression groups. Meanwhile, patients with CD27-positive iTIL-high tumors exhibited better survival than those with iTIL-low tumors. This tendency was weaker in the CD70-high subset. CD70 immunohistochemistry is useful in diagnosing TSCC. CD70 may prevent anti-tumor immunity via CD27. Immunotherapy targeting the CD70–CD27 axis may be a promising option for the treatment of TSCC.

Clinical Significance of Tumor Markers for Advanced Thymic Carcinoma: A Retrospective Analysis from the NEJ023 Study

Simple Summary

Advanced thymic carcinoma (ATC) is rare. Owing to its rarity, there is limited information on the prognostic factors, and the optimal serum tumor markers are also unknown. We conducted a multi-institutional retrospective study of patients with ATC. In this study, we collected data on patient characteristics, progression-free survival (PFS), overall survival (OS), and tumor marker values, and investigated the relationship between tumor marker values and PFS/OS. We found that the neuron-specific enolase (NSE) level may be a useful prognostic tumor marker for ATC, regardless of histology. The findings of the analysis limited to squamous cell carcinoma suggested that the NSE and squamous cell carcinoma antigen levels may be useful prognostic factors.

Abstract

The optimal tumor marker for predicting the prognosis of advanced thymic carcinoma (ATC) remains unclear. We conducted a multi-institutional retrospective study of patients with ATC. A total of 286 patients were treated with chemotherapy. Clinicopathological information, including serum tumor markers, was evaluated to determine the overall survival (OS) and progression-free survival (PFS). The carcinoembryonic antigen, cytokeratin-19 fragment, squamous cell carcinoma (SCC) antigen, progastrin-releasing peptide, neuron-specific enolase (NSE), and alpha-fetoprotein levels were evaluated. In the Kaplan–Meier analysis, the OS was significantly shorter in the patients with elevated NSE levels than in those with normal NSE levels (median, 20.3 vs. 36.8 months; log-rank test p = 0.029; hazard ratio (HR), 1.55; 95% confidence interval (CI), 1.05–2.31 (Cox proportional hazard model)); a similar tendency regarding the PFS was observed (median, 6.4 vs. 11.0 months; log-rank test p = 0.001; HR, 2.04; 95% CI, 1.31–3.18). No significant differences in the OS and PFS were observed among the other tumor markers. In both univariate and multivariate analyses of the patients with SCC only, the NSE level was associated with the OS and PFS. Thus, the NSE level may be a prognostic tumor marker for thymic carcinoma, regardless of histology.

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.

Future Perspective of Chemotherapy and Pharmacotherapy in Thymic Carcinoma

Simple Summary

Thymic carcinoma is a rare cancer, and its biology remains largely unknown. Although complete surgical resection is a standard treatment for thymic carcinoma, systemic chemotherapy is frequently administered in metastatic or recurrent cases. Given the rarity, therapeutic agents are often confirmed on the basis of the results of phase II trials or retrospective studies. Platinum-based combination chemotherapy has long been employed for treating thymic carcinoma. Recently, biomarkers have been explored, and molecular profiles and major oncogenic pathways have gradually been revealed by next-generation sequencing, resulting in the development of targeted therapies. Moreover, clinical trials assessing combination therapy with immune checkpoint inhibitors are ongoing and are expected to be efficacious for treating thymic epithelial tumors. We reviewed the current role of systemic chemotherapy, including targeted therapies and immune checkpoint inhibitors, considering recent findings regarding its biology.

Abstract

Thymic carcinoma is a rare cancer that arises from thymic epithelial cells. Its nature and pathology differ from that of benign thymoma, presenting a poorer prognosis. If surgically resectable, surgery alone or surgery followed by chemoradiotherapy or radiotherapy is recommended by the National Comprehensive Cancer Network Guidelines. Metastatic and refractory thymic carcinomas require systemic pharmacotherapy. Combined carboplatin and paclitaxel, and cisplatin and anthracycline-based regimens have been shown a fair response rate and survival to provide a de facto standard of care when compared with other drugs employed as first-line chemotherapy. Cytotoxic agents have been pivotal for treating thymic carcinoma, as little is known regarding its tumorigenesis. In addition, genetic alterations, including driver mutations, which play an important role in treatments, have not yet been discovered. However, molecular pathways and biomarker studies assessing thymic epithelial tumors have been reported recently, resulting in the development of new agents, such as molecular targeted agents and immune checkpoint inhibitors. As treatment options are currently limited and the prognosis remains poor in metastases and recurrent thymic carcinoma, genetic alterations need to be assessed. In the present review, we focused on the current role of targeted therapies and immune checkpoint inhibitors in treating thymic carcinoma.

Tumor immunity is related to 18 F-FDG uptake in thymic epithelial tumor

Background

2‐deoxy‐2‐[fluorine‐18] fluoro‐d‐glucose (¹⁸F‐FDG) positron emission tomography (¹⁸F‐FDG‐PET) is a convenient modality to assess the metabolic activity within tumor cells. However, there is no consensus regarding the relationship between ¹⁸F‐FDG uptake and the immune environment in thymic epithelial tumors (TETs). We conducted a clinicopathological study to elucidate the relationship between ¹⁸F‐FDG uptake and programmed death ligands 1 and 2 (PD‐L1/PD‐L2) expression in patients with TETs. Methods: A total of 108 patients with histologically confirmed TETs classified as thymomas or thymic carcinomas who underwent surgical resection or biopsy or needle biopsy and ¹⁸F‐FDG PET before any treatment between August 2007 and March 2020 were enrolled in this study. Tumor specimens underwent immunohistochemical staining for PD‐L1, PD‐L2, GLUT1, HIF‐1α, VEGFR2, VEGF‐C, and β2 adrenergic receptor. Results: High uptakes of SUV_max, SUV_mean, MTV, and TLG were identified in 28 (25.9%), 61 (56.5%), 55 (50.9%), and 55 (50.9%) of 108 patients, respectively. High uptake of SUV_max significantly correlated with PS (performance status) of 1–2, thymic carcinoma, and advanced stage, and SUV_max on ¹⁸F‐FDG uptake displayed a close association with PD‐L1 and PD‐L2 expressions, but not with MTV and TLG. Our analysis revealed that SUV_max was identified as being significant relationship for positive PD‐L1/PD‐L2 expression. GLUT1, HIF‐1α, and VEGFR2 were significantly associated with the expression of PD‐L1/PD‐L2 from the biological viewpoint.

Conclusion

¹⁸F‐FDG accumulation was closely associated with the expression of PD‐L1/PD‐L2, which, in turn, was correlated with glucose metabolism and hypoxia. PD‐L1/PD‐L2 could affect the glucose metabolism and hypoxia in thymic tumor cells.

Long-term survival in thymic carcinoma with postoperative pleural dissemination

BACKGROUND

We report a patient with thymic squamous cell carcinoma who underwent multiple rounds of surgical resection and definitive radiotherapy for both primary tumor and postoperative recurrence. However, the patient remains well and healthy 18 years after initial diagnosis. Since long-term survival after postoperative recurrence of thymic carcinoma is extremely rare, we also present her immunohistochemical staining results, which suggested indolent disease.

CASE PRESENTATION

A 42-year-old woman with thymic squamous cell carcinoma underwent en bloc resection of the tumor and thymus gland. Pleural dissemination was noted in the right thoracic cavity 3, 10, and 16 years postoperatively. Where possible, the nodules were resected surgically: during the postoperative 3rd and 16th years. Definitive radiotherapy was administered for all nodules that could not be excised during the postoperative 3rd and 10th years. Disease-free survival is 25 months.

CONCLUSIONS

Local control of pleural dissemination may be beneficial in the treatment of postoperative recurrence of thymic carcinoma in limited cases of indolent disease.

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.

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.

Prognostic impact of PD-1 and PD-L1 expression in malignant pleural mesothelioma: an international multicenter study

BACKGROUND

Programmed cell death 1/programmed death ligand 1 (PD-1/PD-L1) immune-checkpoint blockade is a promising new therapeutic strategy in cancer. However, expression patterns and prognostic significance of PD-L1 and PD-1 are still controversial in human malignant pleural mesothelioma (MPM).

METHODS

Formalin-fixed paraffin-embedded (FFPE) tumor samples from 203 MPM patients receiving standard treatment without immunotherapy were collected from 5 European centers. PD-L1 and PD-1 expression of tumor cells (TCs) and tumor-infiltrating lymphocytes (TILs) were measured by immunohistochemistry and correlated with clinical parameters and long-term outcome.

RESULTS

High (>10%) PD-L1 TC and PD-1 TILs expressions were found in 18 (8%) and 39 (24%) patients, respectively. PD-L1 was rarely expressed by TILs [≥1%, n=13 (8%); >10%, n=1]. No significant associations were found between the PD-L1 or PD-1 expression of TCs or TILs and clinicopathological parameters such as stage or histological subtype. Notably, patients with high (>10%) TC-specific PD-L1 expression exhibited significantly worse median overall survival (OS) (6.3 vs. 15.1 months of those with low TC PD-L1 expression; HR: 2.51, P<0.001). In multivariate cox regression analysis adjusted for clinical parameters, high TC PD-L1 expression (>10%) proved to be an independent negative prognostic factor for OS (HR: 2.486, P=0.005). There was no significant correlation between PD-L1 or PD-1 expression of TILs and OS.

CONCLUSIONS

In this multicenter cohort study, we demonstrate that high (>10%) PD-L1 expression of TCs independently predicts worse OS in MPM. Further studies are warranted to investigate the value of PD-L1/PD-1 expression as a marker for treatment response in MPM patients receiving immunotherapy.

Perspective of Immune Checkpoint Inhibitors in Thymic Carcinoma

Simple Summary

Thymic carcinoma is a rare neoplasm with a poor outcome, and there are no established therapeutic regimens for metastatic or recurrent disease. Immune checkpoint inhibitors (ICIs), such as PD-1/PD-L1 antibodies, are approved in several human cancers, however, ICIs are not approved in thymic carcinoma. Thus, several clinical trials have been undertaken to demonstrate if they are therapeutically effective for patients with thymic carcinoma. In our review, three prospective phase II studies and several case series were discussed in thymic carcinoma. We found that the objective response rate, disease control rate, and progression-free survival in PD-1 blockade monotherapy were approximately 20%, 73%, and four months, respectively. The therapeutic efficacy of PD-1 blockade monotherapy is still limited in patients with thymic carcinoma. Future perspectives focus on the therapeutic implication of tyrokinase inhibitors plus ICIs or new experimental agents plus ICIs alongside several ongoing experimental studies.

Abstract

Thymic carcinoma is a rare neoplasm with a dismal prognosis, and there are no established therapeutic regimens for metastatic or recurrent disease. Immune checkpoint inhibitors (ICIs), such as PD-1/PD-L1 antibodies, are widely approved in several human cancers, contributing to prolonging survival in thoracic tumors. Thymic carcinoma exhibits histologic properties of squamous cell carcinoma (SQC), and resembles the SQC of the lung. ICIs are not approved in thymic carcinoma. Thus, several clinical trials have been undertaken to demonstrate if they are therapeutically effective for patients with thymic carcinoma. In our review, three prospective phase II studies and several case series were discussed in thymic carcinoma. We found that the objective response rate, disease control rate, and progression-free survival in PD-1 blockade monotherapy were approximately 20%, 73%, and four months, respectively. Two exploratory investigations indicated that PD-L1 within tumor cells exhibits a possibility of the therapeutic prediction of PD-1 blockade in thymic carcinoma. Several case reports, alongside their treatment content, have also been reviewed. The therapeutic efficacy of PD-1 blockade monotherapy is still limited in patients with thymic carcinoma. Future perspectives focus on the therapeutic implication of tyrokinase inhibitors plus ICIs or new experimental agents plus ICIs alongside several ongoing experimental studies.

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.

Immunobiology of Thymic Epithelial Tumors: Implications for Immunotherapy with Immune Checkpoint Inhibitors

Thymic epithelial tumors (TETs) are a group of rare thoracic malignancies, including thymic carcinomas (TC) and thymomas (Tm). Autoimmune paraneoplastic diseases are often observed in TETs, especially Tms. To date, chemotherapy is still the standard treatment for advanced disease. Unfortunately, few therapeutic options are available for relapsed/refractory TETs. In the last few years, the deepening of knowledge on thymus' immunobiology and involved altered genetic pathways have laid the foundation for new treatment options in these rare neoplasms. Recently, the immunotherapy revolution has landed in TETs, showing both a dark and light side. Indeed, despite the survival benefit, the occurrence of severe autoimmune treatment-related adverse events has risen crescent uncertainty about the feasibility of immunotherapy in these patients, prone to autoimmunity for their cancer biology. In this review, after summarizing immunobiology and immunopathology of TETs, we discuss available data on immune-checkpoint inhibitors and future perspectives of this therapeutic strategy.

PD-L1 expression in bone marrow plasma cells as a biomarker to predict multiple myeloma prognosis: developing a nomogram-based prognostic model

PD-L1 expression is associated with poor prognosis, although this relationship is unclear in bone marrow-derived haematologic malignancies, including multiple myeloma. We aimed to determine whether PD-L1 expression could predict the prognosis of newly diagnosed multiple myeloma (NDMM). We evaluated 126 NDMM patients (83, retrospectively; 43, prospectively) who underwent bone marrow examinations. Bone marrow aspirates were analysed for PD-L1 expression, categorized as low or high expression, using quantitative immunofluorescence. High PD-L1 expression could independently predict poor overall survival (OS) (95% CI = 1.692-8.346) in multivariate analysis. On subgroup analysis, high PD-L1 expression was associated with poor OS (95% CI = 2.283-8.761) and progression-free survival (95% CI = 1.024-3.484) in patients who did not undergo autologous stem cell transplantation (ASCT) compared with those who did. High PD-L1 expression was associated with poor OS despite frontline treatments with or without immunomodulators. Thus, PD-L1 expression can be a useful prognosis predictor in NDMM patients, whereas ASCT may be used in patients with high PD-L1 expression. We developed a prognostic nomogram and found that a combination of PD-L1 expression in bone marrow plasma cells and clinical parameters (age, cytogenetics, and lactate dehydrogenase) effectively predicted NDMM prognosis. We believe that our nomogram can help identify high-risk patients and select appropriate treatments.

Prognostic relevance of programmed cell death protein 1/programmed death-ligand 1 pathway in thymic malignancies with combined immunohistochemical and biomolecular approach

BACKGROUND

The aim of the study was to investigate Programmed cell Death protein 1 (PD-1) and Programmed Death-Ligand 1 (PD-L1) and their mRNA expression in thymic epithelial tumors (TETs).

RESEARCH DESIGN AND METHODS

We analyzed 68 samples of formalin-fixed paraffin-embedded tissue (63 thymomas and 5 thymic carcinomas). PD-1 and PD-L1 protein expression were evaluated by immunohistochemistry, and mRNA expression was evaluated by real-time PCR.

RESULTS

M/F ratio was 33/35, and median age was 60.5 years. Twenty patients had Myasthenia Gravis (MG). In the subgroup with large tumors (>5 cm), PD-L1 mRNA overexpression was significantly associated with worse prognosis vs. patients with no mRNA overexpression (p = 0.0083) and simultaneous PD-L1 immunostaining (>1%); PD-L1 mRNA overexpression was significantly associated with worse prognosis, respect to patient with PD-L1 negative immunostaining, and no PD-L1 mRNA overexpression (p = 0.0178). The elderly patients (>60 years) with large tumors showed worse prognosis (p = 0.0395). PD-L1 immunostaining (>50%) resulted to be significantly associated with MG.

CONCLUSIONS

Our data suggest the potential involvement of the PD-1 and PD-L1 pathway in TETs' progression. According to our results, it may be helpful to design future trials with anti-PD-1 drugs to establish high-risk patients after surgery.

Programmed death 1 ligand (PD-L1) in solid cancers after allogeneic hematopoietic stem cell transplantation: a retrospective analysis by the Nagasaki Transplant Group

Programmed death 1 ligand (PD-L1) is an immunomodulatory molecule expressed by cancer cells, and it has been widely demonstrated to inhibit host antitumor responses. The aim of the present study was to identify clinicopathological features associated with PD-L1 expression in the secondary solid cancers of patients after allogeneic hematopoietic stem cell transplantation. In this database of 530 patients who received allo-HSCT between 1990 and 2017, 15 developed solid cancers with a median interval of 3487 days after transplantation. Three patients had 2 different solid cancers. Eighteen solid cancer cases were identified. A multivariate analysis showed that chronic graft-versus-host disease (GVHD) was associated with an increased risk of solid cancer. The presence of chronic GVHD was observed in 8 out of 18 cases at the diagnosis of secondary malignancies. PD-L1 expression levels in cancers were significantly higher in patients with active chronic GVHD than in those without chronic GVHD (P = 0.020). Five cases of cancer that developed in the involved organs of chronic GVHD showed 30% or higher PD-L1 positivity. The present results revealed distinct PD-L1 expression in the secondary solid cancers of post-transplant patients with chronic GVHD.

CD20+ tumor-infiltrating immune cells and CD204+ M2 macrophages are associated with prognosis in thymic carcinoma

Thymic carcinoma is a rare malignant disease with no standard systemic chemotherapy. The purpose of the present study was to investigate tumor‐infiltrating immune cells (TIIC) in the tumor microenvironment (TME), focusing on the impact of TIIC and program death‐ligand 1 (PD‐L1) expression on clinical outcomes in thymic cancer. Patients with thymic carcinoma resected between 1973 and 2017 were investigated. The tissue specimens were analyzed through immunohistochemical staining to elucidate the prognostic effects of TIIC, their ratios and PD‐L1 in a preliminary cohort (n = 10). The density of TIIC as well as PD‐L1 expression was evaluated in intraepithelial and tumor‐stromal areas on the representative whole section of tumors. The immune factors showing significant association with disease‐free survival (DFS) were evaluated in the total cohort (n = 42). TIIC in the preliminary population showed no significant difference between the two groups. However, CD8, CD20, CD204, FOXP3 and CD20/CD204 ratio demonstrated a tendency to act as predictive markers for recurrence. In the total cohort, significant differences were observed for CD8⁺, CD20⁺ and CD204⁺ cells in tumor islets, and for CD8⁺, CD20⁺ and FOXP3⁺ cells as well as the CD8/CD204 and CD20/CD204 ratios in the stroma, indicating their prognostic effect. The prognostic effect of the PD‐L1 expression in tumor cells could not be established, possibly because of intratumoral heterogeneity. CD8, CD20 and CD204 positive TIIC in stroma were identified as possible better prognostic biomarkers, considering the heterogeneity of other biomarkers. The present study paves the way for exploring strategies of combination immunotherapy targeting B cell immunity in thymic carcinoma.

PD-L1 expression level in different thymoma stages and thymic carcinoma: a meta-analysis

BACKGROUND

The immune checkpoint ligand, programmed cell death 1 ligand 1 (PD-L1), is expressed in various tumors and associated with response to drugs that target programmed cell death protein 1. Previous studies have estimated the level of PD-L1 expression among different stages of thymoma and thymic carcinoma to evaluate its potential use as a diagnostic factor; however, its varying expression level has been problematic. We conducted this meta-analysis of published literature to evaluate PD-L1 expression in thymomas and thymic carcinomas.

METHODS

We analyzed 12 studies that included 320 patients with type A/AB/B1 thymoma, 225 patients with type B2/B3 thymoma, and 180 patients with thymic carcinoma.

RESULTS

No difference in PD-L1 expression level was found between the B2/B3 vs C groups (odds ratio [OR], 0.67; 95% confidence interval [CI], 0.26, 1.76; p = 0.42). However, the heterogeneity was very high (I² = 78%), and a significant difference was found between groups A/AB/B1 and B2/B3 (OR, 0.22; 95% CI, 0.12, 0.41; p < 0.001), with a relatively low heterogeneity (I² = 55%).

CONCLUSION

PD-L1 positivity might be a useful factor to differentiate type A/AB/B1 thymoma from type B2/B3 and thymic carcinoma. This result might be valuable for potential anti PD-L1 treatment in thymoma and thymic carcinoma.

Next-generation sequencing in thymic epithelial tumors uncovered novel genomic aberration sites and strong correlation between TMB and MSH6 single nucleotide variations

Thymic epithelial tumors (TET) including thymomas and thymic carcinomas are rare, but they are common primary tumors in the anterior mediastinum. The etiology and tumorigenesis of TET remain unclear. To better understand the novel aberrations of this rare tumor and provide more significant mutation sites for targeted therapy, we performed next-generation sequencing detection on 55 patients with TET. Our results showed that most genes in 12 core pathways harbored aberrations of indeterminate potential. In 4 genes (ARID1A, KMT2C, TGFBR2 and MAP3K1), the indel frequency was above 90%. Dozens of genes, including TGFBR2, KMT2C, PRKDC, ATR, CHD2, SDHA, KDM5A, CHEK1, MSH6 and POLE, possessed frameshift indel with different frequencies in different hotspot sites, which could be the new targets of therapy for TET. For the first time, we revealed a strong correlation between the tumor mutational burden and single nucleotide variations, but not frameshift, on DNA mismatch repair gene MSH6 in TET.

Clinicopathologic Significance and Immunogenomic Analysis of Programmed Death-Ligand 1 (PD-L1) and Programmed Death 1 (PD-1) Expression in Thymic Epithelial Tumors

Objectives: Thymic epithelial tumors (TETs) are rare malignant tumors that exhibit heterogeneous histology and clinical behavior. As immune check point inhibitors, drugs targeting anti-programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) have shown remarkable results against many cancers; thus, the importance of PD-1/PD-L1 immunohistochemistry as a predictive or prognostic biomarker has grown. However, limited data on PD-L1 and PD-1 expression in TETs have been reported; moreover, these results have been variable. Here, we examined the expression of PD-1/PD-L1 proteins in TETs and analyzed the clinicopathologic significance of this expression.

Patients and Methods: A tissue microarray was constructed using 368 samples of TETs, each in triplicate. Immunohistochemistry for PD-L1 (SP263 assay) and PD-1 in TETs and CD8 in thymic carcinoma (TC) was performed; next, correlations with clinicopathologic characteristics were analyzed. PD-L1^high was designated as ≥50% of tumor proportion score; PD-1^high and CD8^high were defined as ≥5% and 1% of tumoral immune cells, respectively.

Results: The cohort consisted of 308 patients with thymomas and 60 patients with TC. PD-L1 positivity was identified in 90.6% (328/362, ≥1%) of TETs, PD-1 expression of intra-/peritumoral T cells was identified in 53.6% (194/362) of TETs and CD8 positivity was identified in 11% (7/60, ≥1%) of TC. Of the 362 patients, 141 (39.0%) exhibited high PD-L1 expression (PD-L1^high). The PD-L1^high thymoma group was correlated with high Masaoka-Koga stage (p < 0.001), type B3 histology (p < 0.001), and myasthenia gravis (p < 0.001). This group exhibited poor overall survival (OS, p = 0.003, log-rank) and worse disease-free survival (DFS, p = 0.042, log-rank). No survival differences were detected between PD-L1^high and PD-L1^low groups in TC. Additionally, there was no correlation between PD-1 expression and survival in patients with TETs. Multivariate analysis revealed that PD-L1^high expression was an independent poor prognostic factor (p = 0.047, HR 2.087, 95% CI, 1.009–4.318) in thymomas.

Conclusions: To our knowledge, this is the largest study on TETs published in English literature. This study provides useful information regarding the prognosis of and potential therapeutic options for patients with TETs.

Immune checkpoints in thymic epithelial tumors: challenges and opportunities

Thymic malignancies are rare mediastinal cancers, classified according to the World Health Organization's histopathologic classification which distinguishes thymomas from thymic carcinomas. One key consideration when discussing immunotherapy for thymic epithelial tumors is that one-third of patients diagnosed with thymomas present at the time of diagnosis with autoimmune disorders, the most common being myasthenia gravis. The first step in the understanding of autoimmunity in thymic epithelial tumors is to distinguish true autoimmune disorders from paraneoplastic syndromes; besides pathophysiology, clinical correlates, impact on oncological management and survival may differ strongly. Autoimmune disorders are related to a deregulation in the physiological role of the thymus (i.e. to induce central tolerance to tissue self-antigens) through control of differentiation and subsequent positive and negative selection of immature T cells; from a clinical standpoint, in thymomas, once autoimmune disorders are present, they may not regress significantly after thymectomy. PD-L1 expression, while observed in more than 90% of epithelial cells of the normal thymus with a medullar tropism respecting Hassall's corpuscles, has also been identified in thymomas and thymic carcinomas using various immunohistochemistry protocols. Immune checkpoint inhibitors of the PD-1/PD-L1 axis have been assessed in advanced and metastatic thymic epithelial tumors, mainly thymic carcinomas. Several case reports have been published, and four trials have assessed the efficacy and safety of these inhibitors. Immunotherapy is not standard given the frequent occurrence of severe autoimmune disorders, and clinical trials are ongoing.

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Thymic malignancies are rare tumors.

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Advanced, metastatic and refractory thymic tumors may be treated with chemotherapy.

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Autoimmune disorders, such as myasthenia gravis, are observed in 30% of cases.

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PD-L1 expression is a hallmark of thymic epithelial cells.

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Immunotherapy is not standard, given the occurrence of autoimmune disorders.

The nephrotoxicity of new immunotherapies

Introduction: Advanced cancers that did not respond to chemotherapy were once a death sentence, but now there are newer therapies utilizing the patient's own immune system to fight cancer that are proving effective in chemotherapy-refractory malignancies. However, this success against cancer cells may be accompanied by immune-related adverse events that can affect the kidneys. Areas covered: Using Medline and Scopus, we compiled all publications through February 2019 that pertained to immune checkpoint inhibitors (ICPIs) and chimeric antigen receptor T-cells (CAR T-cells).  The focus of this review is the discussion of these new cancer therapies, with attention to the reported kidney-related adverse effects.. Expert opinion: Autoimmunity is repressed by molecular pathways that inhibit T-cell activation against selected antigens. These self-protective mechanisms have been appropriated by tumor cells as a means of evading immune detection and destruction. New immunotherapies such as immune checkpoint inhibitors and chimeric antigen receptor T-cell therapy incite an aggressive immune response directed against tumor cells. This unrestrained activation of the immune system may result in kidney injury via multiple mechanisms.

Clinical significance of programmed death 1/programmed death ligand 1 pathway in gastric neuroendocrine carcinomas

BACKGROUND

Recently, more and more studies have demonstrated the pivotal role of programmed death 1/programmed death ligand 1 (PD-1/PD-L1) pathway in the immune evasion of tumors from the host immune system. However, the role of PD-1/PD-L1 pathway in gastric neuroendocrine carcinomas (G-NECs) remains unknown.

AIM

To investigate the expression of PD-1/PD-L1 and role of PD-1/PD-L1 pathway in G-NECs, which occur rarely but are highly malignant and clinically defiant.

METHODS

We investigated the expression of PD-L1 on tumor cells and PD-1⁺, CD8⁺, and FOXP3⁺ T cell infiltration by immunohistochemistry in 43 resected G-NEC tissue specimens. The copy number alterations of PD-L1 were assessed by qRT-PCR.

RESULTS

Most of the G-NECs tumor cells exhibited a near-uniform expression pattern of PD-L1, while some showed a tumor-stromal interface enhanced pattern. Of the 43 G-NECs, 21 (48.8%) were classified as a high PD-L1 expression group, and the high expression of PD-L1 was associated with poor overall survival (OS). The high expression of PD-L1 was correlated with abundant PD-1⁺ tumor infiltrating lymphocytes (TILs) instead of CD8⁺ TILs and FOXP3⁺ regulatory T cells (Tregs). Our analysis also suggested that the infiltration of CD8⁺ TILs tended to be a favorable factor for OS, although the difference did not reach the statistical significance (P = 0.065). Meanwhile, PD-L1 was significantly overexpressed in cases with copy number gain as compared with those without.

CONCLUSION

Our data demonstrated for the first time that high expression of PD-L1 in G-NECs is associated with a poor prognosis, while the high expression may be due to the copy number variation of PD-L1 gene or stimulation of TILs. These results provide a basis for the immunotherapy targeting PD-1/PD-L1 pathway in G-NECs.

The prognostic impact of programmed cell death 1 and its ligand and the correlation with epithelial-mesenchymal transition in thymic carcinoma

Background

The significance of epithelial‐mesenchymal transition (EMT) and immune checkpoint proteins in thymic carcinoma remains unknown. We examined the clinical significance of EMT, tumor‐infiltrating lymphocytes expressing the immune checkpoint protein, programmed cell death 1 (PD‐1 + TILs), and the expression of PD‐1 ligand 1 (PD‐L1) in thymic carcinoma (TC). We also investigated the relationships between these immune checkpoint proteins and the EMT status and examined the impact of induction chemotherapy on patients with tumors that express these proteins.

Methods

The relationship between PD‐1 + TILs/PD‐L1 and clinicopathological findings including EMT was investigated by immunohistochemistry (IHC) of surgically resected samples from 43 patients with TC. In 15 patients receiving induction therapy (IT), those factors were compared before and after IT.

Results

With IHC, 26 cases (60.5%) were positive for PD‐L1, and 19 cases were positive for PD‐1 + TILs (44.2%). The disease‐free survival rate in patients showing EMT and who were PD‐1/PD‐L1 positive was significantly worse compared to negative cases (EMT; P = 0.0095, PD‐1; P = 0.001, PD‐L1; P = 0.0037). We found a significant relationship between PD‐L1 and EMT status (P = 0.01). In patients who received IT, PD‐L1 increased, and the change was strongly correlated with EMT status (P = 0.01).

Conclusion

Epithelial‐mesenchymal transition, PD‐L1, and PD‐1 + TILs have prognostic impact, and PD‐L1 is correlated with EMT status. PD‐L1 expression after IT was significantly higher compared to before IT and was correlated with the EMT change. Thus, PD‐L1 may be upregulated during EMT, and anti‐PD‐1/PD‐L1 immunotherapy may provide reliable treatment of TC in combination with chemotherapy.

PD-L1 and immune infiltrates are differentially expressed in distinct subgroups of gastric cancer

This study investigates the association of PD-L1 expression and immune cell infiltrates and their impact on clinical outcome, in addition to their overlap with microsatellite instability (MSI), HER2 and ATM molecular subgroups of gastric cancer (GC). PD-L1 membrane expression on tumour cells (TC) and infiltrating immune cells (IC), CD3 + T-lymphocytes, CD8+ cytotoxic T-cells, ATM and HER2 were assessed by immunohistochemistry (IHC) in the ACRG (Asian Cancer Research Group) GC cohort (N = 380). EBV status was determined using in situ hybridization and MSI status was performed using PCR and MLH1 IHC. The PD-L1 segment was associated with increased T-cell infiltrates, while the MSI-high segment was enriched for PD-L1, CD3, and CD8. Multivariate analysis confirmed PD-L1 positivity, high CD3 and high CD8 as independent prognostic factors for both disease-free survival and overall survival (all p < 0.05). Patients with MSI-high tumours had better overall survival by both univariate and multivariate analysis. The ATM-low and HER2-high subgroups differed markedly in their immune profile; the ATM-low subgroups enriched for MSI, PD-L1 positivity and CD8 + T-cells, while the HER2 segment was enriched for MSS, with no enrichment for immune markers. Hence, we demonstrate a molecular profiling approach that can divide GC into four molecular subgroups, namely ATM-low, HER2-high, PD-L1 positive and MSI-high with differing levels of immune infiltrates and prognostic significance which may help to stratify patients for response to targeted therapies.

PD-L1 expression in pancreatic adenosquamous carcinoma: PD-L1 expression is limited to the squamous component

AIM

We examined the programmed death-ligand 1 (PD-L1) expression in surgically resected pancreatic adenosquamous carcinoma (PASC) samples. Furthermore, the detection rate was also assessed using biopsy cases obtained from endoscopic ultrasound-guided fine needle aspiration (EUS-FNA).

METHODS

Fifteen cases of PASC (six resected and nine EUS-FNA biopsied) from the Kurume University Hospital between 2009 and 2016 were used for the evaluation of PD-L1 expression. As a control group, 34 cases of pancreatic ductal adenocarcinomas (PDACs) were selected. To compare　the positivity and intensity of PD-L1, two types of clones (SP263, E1L3N) were examined for immunostaining. Only the membrane expression of PD-L1 was regarded as positive. The PD-L1 expressions in the squamous cell carcinoma component (SCc), adenocarcinoma component (ACc), and immune cells were assessed separately. The ratio of PD-L1 expression was calculated by counting the positive tumor cells, and tumor proportion score (TPS) was applied (TPS; Null < 1%, low expression; 1 ≤ TPS ≤ 49% and high expression; ≥ 50%).

RESULTS

PD-L1 expression was observed in five surgical PASC samples (83%). This shows that SCc presented a high expression in these cases. However, the overall TPS indicated a low expression. In contrast, only one case (3%) was positive for PD-L1 in PDACs, and the TPS indicated a low expression. No differences in PD-L1 expression were observed between the two clones, SP263 and E1L3N. High PD-L1 expression in the EUS-FNA sample was found in only one case (11%).

DISCUSSION

Although assessment using the tumor cells of PASC samples obtained from EUS-FNA was difficult, this study suggests the selective expression of PD-L1 in the SCc of PASC. Furthermore, it was considered that immune checkpoint inhibitors could provide therapeutic effects selectively on the SCc for the entire range of TPSs, though the PD-L1 expression was low.

Expression of PD-L1/PD-1 in lymphoepithelioma-like carcinoma of the thymus

Poorly differentiated non-keratinizing squamous cell carcinoma of the thymus, also known as lymphoepithelioma-like carcinoma, is a rare primary malignant neoplasm of thymic origin. The mainstay of treatment for these tumors is surgical and they tend to respond poorly to chemotherapy. The checkpoint programmed cell death ligand-1 protein (PD-L1) bound to its receptor (PD-1) has been demonstrated to be an important therapeutic target for many different tumors. Expression of PD-L1/PD-1 in lymphoepithelioma-like carcinoma of the thymus may indicate that these tumors are potential targets for inhibitor therapy. Twenty-one cases of lymphoepithelioma-like carcinoma of the thymus were collected and reviewed. Tissue microarrays were created using triplicate 2 mm cores for each case. PD-L1/PD-1 staining pattern (neoplastic cells versus tumor infiltrating lymphocytes) was documented for each case. Out of 21 cases, 15 (71.4%) showed various degrees of membranous PD-L1 staining. Of the positive cases, 48% showed high expression of PD-L1 (>50% of tumor cells) and 24% showed low expression (<50%). PD-1 staining showed focal positivity in 12/20 (60%) cases among tumor infiltrating lymphocytes. PD-L1/PD-1 inhibitor therapy has been applied successfully in other solid malignant tumors with high expression of PD-L1/PD-1. The high level of PD-L1 expression in our cases indicates that PD-L1 may play a role in the pathogenesis of these tumors and that PD-L1/PD-1 blockade may be a viable therapeutic option for patients with lymphoepithelioma-like carcinoma of the thymus who have failed other first-line therapies.

PD-1/PD-L1 expressions in medullary thyroid carcinoma: Clinicopathologic and prognostic analysis of Chinese population

INTRODUCTION

Few studies have focused on PD-L1 expression in medullary thyroid carcinoma (MTC). Expressions of PD-1 and PD-L1 and their clinicopathologic and prognostic relevance were therefore further investigated on a relatively large population of MTC patients.

MATERIALS AND METHODS

Surgical specimens were obtained from 87 MTC patients during a median follow-up of 37.7 months. PD-1 and PD-L1 expressions on tumor and associated immune cells were studied immunohistochemically using >1% positive cells as a threshold for positivity. Their correlations with clinicopathologic and prognostic feature were analyzed.

RESULTS

PD-1 and PD-L1 were positively stained in 22 and 19 MTC patients. Most PD-L1-positive cases (18/19) showed weak to moderate staining intensity. PD-1 and PD-L1 were co-expressed in 11 patients. PD-L1 positivity was significantly correlated with distant metastases at surgery (21.1% vs 1.5%, P = 0.007). Coexpression of PD-1 and PD-L1 in MTC was correlated with advanced pathologic TNM stage III/IV (P = 0.040) and distant metastases at surgery (P = 0.013). However, there was no other clinicopathologic and prognostic relevance regarding to PD-1, PD-L1 or their coexpression in our MTC patients.

CONCLUSION

PD-1/PD-L1 pathway was expressed in MTC patients and was significantly correlated with the distant metastases at surgery, which may shed light on PD-1/PD-L1 as a promising therapeutic target in MTC. Future better understanding of PD-1/PD-L1 expression and their relationship with immunotherapy response may provide direct evidence for management of refractory MTC.

Clinicopathological significance of tumor-infiltrating lymphocytes and programmed death-1 expression in cutaneous melanoma: a comparative study on clinical subtypes

Interactions between immune cells and tumor cells play an important role in tumor progression. We evaluated patterns of tumor-infiltrating lymphocytes (TILs) and programmed death-1 (PD-1) expression in acral and nonacral cutaneous melanoma, and determined their effects on clinicopathological characteristics and biologic responses. We identified 122 cases of cutaneous melanoma, of which 39 were cases of non-nail unit acral melanoma (NNUAM), 35 were cases of nail unit melanoma (NUM), and 48 were cases of nonacral melanoma. Clinicopathological features and survival outcomes were analyzed according to the scores for TILs and PD-1 expression in intratumoral and peritumoral compartments. The effects of the presence of TILs and PD-1 expression on various clinicopathological factors differed according to the clinical subtypes of cutaneous melanoma. The frequency of intratumoral TILs and PD-1 expression were lower in NUM than in the other two subtypes. The density of peritumoral PD-1 was significantly higher in NNUAM. In NUM and nonacral melanoma, a low density of intratumoral TILs and PD-1 was associated with a deeper Breslow thickness and the presence of a vertical growth phase. In NNUAM, a high density of peritumoral TILs and PD-1 was associated with a shallower Breslow thickness and less frequent extracutaneous dissemination. In NNUAM, a high density of peritumoral PD-1 was associated with a better prognosis. This study suggests that the effects of PD-1+ TILs on biological activity differ according to the clinical subtypes of cutaneous melanoma.

Different pattern of PD-L1, IDO, and FOXP3 Tregs expression with survival in thymoma and thymic carcinoma

OBJECTIVES

The expression of immune checkpoint ligand PD-L1 has been reported in various tumors. The expression of IDO and FOXP3 Tregs are considered to be associated with tumor-induced tolerance and poor outcome. Their prognostic role in surgically treated thymoma and thymic carcinoma, however, has not been investigated.

MATERIALS AND METHODS

Tissue microarray (TMA) blocks comprised of 100 surgically treated thymomas and 69 surgically treated thymic carcinomas were conducted. Tissue sections were incubated with primary antibodies against PD-L1 (clone E1L3N, 1:100), IDO (clone 10.1, 1:50), and FOXP3 (clone 236 A/E7, 1:50). Comparisons for categorical variables were performed using χ² test and Fisher's exact test. Survival analysis was established using Kaplan-Meier method and log-rank test. Univariate and multivariate analyses were performed using Cox regression model.

RESULTS AND CONCLUSIONS

High expression of PD-L1, IDO, and FOXP3 Tregs were identified in 36 (36%), 13 (13%), and 16 (16%) thymoma patients, respectively. High expression of PD-L1, IDO, and FOXP3 Tregs was associated with higher grade of tumor histology (P <  0.001, P =  0.007, and 0.014, respectively). High expression of PD-L1 was also associated with advanced Masaoka staging (P <  0.001). In patients with thymic carcinoma, high expression of PD-L1, IDO, and FOXP3 Tregs were identified in 25 (36%), 10 (14%), and 20 (29%) patients, respectively. Complete resection, low expression of IDO, and high expression of FOXP3 Tregs were associated with better overall survival (P =  0.001, 0.004, and 0.032, respectively), and progression-free survival (P <  0.001, P =  0.026, and 0.047, respectively) in multivariate analysis. In surgically treated thymoma, high PD-L1 expression was associated with advanced Masaoka staging. High PD-L1, IDO, and FOXP3 Tregs expression was associated with high grade histology. In surgically treated thymic carcinoma, significant survival benefit was noted in patients with complete resection, low IDO expression, and high FOXP3 Tregs expression.

Impact of PD-L1, transforming growth factor-β expression and tumor-infiltrating CD8+ T cells on clinical outcome of patients with advanced thymic epithelial tumors

BACKGROUND

Advanced thymic epithelial tumors (TETs) are indolent and poorly responsive to chemotherapy. PD-1/PD-L1 inhibitors have shown remarkable clinical benefit in several cancers; however, many immunomodulatory molecules have been identified that affect the immune response. This study examined the progonostic roles of PD-L1, transforming growth factor-β (TGF-β), and CD8⁺ tumor-infiltrating lymphocytes (CD8⁺ TILs) in patients with TETs.

METHODS

Retrospective analysis was performed on the data of 20 patients with stage IV thymic carcinoma and 13 with stage III/IV invasive thymoma. Tissue biopsies were obtained before first-line chemotherapy was administered. Protein levels were assessed by immunohistochemistry. Objective response rate, overall survival (OS), and progression-free survival (PFS) were analyzed.

RESULTS

Patients with advanced thymic carcinoma exhibited higher levels of PD-L1 and TGF-β than patients with advanced invasive thymic carcinoma (PD-L1: 65.0% vs. 46.2%, P = 0.472; TGF-β: 65.0% vs. 15.4%, P = 0.011). Five advanced thymic carcinoma patients with low levels of PD-L1 and TGF-β exhibited high levels of CD8 staining. The median OS was 29.5 months patients with high TGF-β expression versus 62.9 in patients with low TGF-β (P = 0.052). In patients with advanced thymic carcinoma, the median PFS in the high PD-L1 expression group was 13.3 months versus 23.5 (P = 0.043) in the low PD-L1, and the median OS was 50.7 months in the high CD8 expression versus 15.1 in the CD8 low group (P = 0.154).

CONCLUSIONS

Our results showed the prognostic roles of PD-L1, TGF-β, and CD8⁺ TILs in patients with advanced TETs, and the potential for development of anti-PD-1/PD-L1 therapies.

PD-L1 Expression Predicts a Distinct Prognosis in Krukenberg Tumor with Corresponding Origins

Krukenberg tumor (KT) is an uncommon ovarian metastatic signet-ring cell adenocarcinoma that mostly metastasizes from gastrointestinal carcinoma. Optimal treatment options for KTs are limited. Programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) inhibitors have shown remarkable activity in clinical trials for metastatic tumors. Here, we evaluated PD-L1 expression and T cell infiltration in KTs and their corresponding primary tumors. Positive tumor PD-L1 expression was detected in 9 (25.7%) KTs from gastric carcinomas (GCs) and in 20 (66.7%) KTs from colorectal carcinomas (CRCs). Patient survival was assessed according to the PD-L1 status and CD8⁺ T cell density. Positive tumor PD-L1 expression in KTs from GCs was associated with poor prognosis. In contrast, positive tumor PD-L1 expression in KTs from CRCs was associated with an improved prognosis. We analyzed copy number variations of the PD-L1 gene in KTs. PD-L1 expression was higher in cases with copy number gains. The T cell densities within KTs and their corresponding primary tumors were compared. The densities of CD8⁺ T cells correlated significantly between the primary tumors and KTs from the same case. Taken together, the research further highlighted targets for immune-based therapy in KTs from GCs and CRCs.

Thymic tumors and immune checkpoint inhibitors

Thymoma and thymic carcinoma, known as the most common features of thymic epithelial tumors (TETs), are thoracic malignancies displaying varied clinical features and prognosis. These neoplasms being frequently ineligible for surgical complete resection as a curative treatment because of extensive tumor spread, effectual nonsurgical treatments are needed; however, an optimal chemotherapeutic regimen has not been identified, although some regimens have been shown to be active. Immunotherapy is effective for other malignancies and may be promising as a therapeutic alternative for refractory TETs. Thus far, several studies have determined the expression of programmed death ligand 1 (PD-L1) and programmed death 1 (PD-1) in TETs, including its clinicopathological and prognostic significance. The results have been conflicting due to the different immunohistochemical antibodies employed and distinct cutoff values. However, many authors identified abundant PD-L1 expression in TETs, which is considered as an important predictive factor for therapeutic effect of PD-1 inhibitors in other malignant tumors. In some clinical trials, an acceptable clinical efficacy of PD-1 inhibitor for TETs has been reported as expected; however, concerns regarding immunological adverse events have been raised. To optimize these therapeutic agents for refractory TETs, additional studies which evaluate clinical availabilities of immunotherapeutic drugs and characterize their basic mechanisms of action against immunotherapeutic targets are both urgently required.

Expression Patterns, Prognostic Value, and Intratumoral Heterogeneity of PD-L1 and PD-1 in Thymoma and Thymic Carcinoma

INTRODUCTION

Thymic epithelial tumors (TETs) including thymoma and thymic carcinoma are rare tumors with little data available to guide treatment. Immunotherapy with checkpoint blockade has shown promising activity, but data regarding the expression patterns and prognostic implications of programmed death 1 (PD-1) and its ligand (PD-L1) in TETs have yielded conflicting results. Intratumoral heterogeneity of PD-1/L1 expression has been shown in other cancers, but has not been described in the TET literature.

METHODS

We performed a retrospective single-center review of 35 patients with resected TET. PD-1/L1 expression was assessed by immunohistochemistry using PD-1 clone: NAT105 and PD-L1 clone: 22C3. Tumor samples from 35 patients were evaluated including 32 patients with thymoma and 3 patients with thymic carcinoma.

RESULTS

PD-L1 expression was detected in 83% (29 of 35) tumor samples, including 100% (3 of 3) of thymic carcinoma patients and 81% (26 of 32) of thymoma patients. PD-1 expression was detected in 77% (27 of 35), including 33% (1 of 3) of thymic carcinoma patients and 81% (26 of 32) thymoma patients. High PD-1 expression was associated with lower grade tumors. Unlike prior studies, PD-L1 expression was not associated with higher grade tumors or higher stage. Neither PD-L1 nor PD-1 expression was significantly associated with survival. Three patients with thymoma had multiple tumor sections evaluated for expression of PD-1/L1, with differing expression patterns of both PD-L1 and PD-1 observed in two patients.

CONCLUSIONS

This study confirms high expression of PD-L1 and PD-1 in TET and shows for the first time intratumoral heterogeneity of PD-L1 and PD-1 in thymoma patients.

Correlation between the Expression of PD-L1 and Clinicopathological Features in Patients with Thymic Epithelial Tumors

The incidence of thymic epithelial tumors (TETs) in the Chinese population was much higher than that in the North American population. In clinical treatment, the prognosis of benign tumors after surgical resection was significantly better than that of malignant tumors. Currently, the commonly used clinical indicators for TET staging included Masaoka staging and WHO (2015) pathological criteria; however, the distinction between the benign and malignant tumors and diagnosis is yet to be explored. The current study demonstrated that the expression of PD-L1 in tumor cells was correlated with the degree of TET malignancy. The quantitative analysis of PD-L1 expression in 70 cases of TET tumor samples revealed that the positive rate of PD-L1 expression in types A, AB, B1, and B2 of thymoma (40 cases) was 37.5% (15/40), which was significantly lower than that in type B3 thymoma and thymic carcinoma (76.67%, 30 cases, 23/30) as demonstrated by chi-square test (P < 0.05). In addition, the two methods were analyzed for the quantitative detection of PD-L1 expression. The results from the estimation of transcriptional RNA expression and quantitative protein immunohistochemistry were consistent (r = 0.745). Furthermore, we also analyzed PD-L1 expression level in different types of TETs from TCGA database and observed that higher PD-L1 expression was in thymic carcinoma than in thymoma. Therefore, it could be concluded that PD-L1 expression in TET cells was correlated with the degree of malignancy, whereas the estimation of PD-L1 expression was potentially applicable in the clinical staging of TETs.