Insulin-Like Growth Factor-1 Receptor Expression in Thymic Malignancies

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.

Evolving treatment landscape in thymic epithelial tumors: From mechanism to therapy

Thymic epithelial tumors (TETs) are rare neoplasms of the anterior mediastinum that arise from thymic epithelial cells. Although surgery is the preferred treatment for resectable TETs, the options for unresectable or recurrent advanced-stage TETs are limited beyond platinum-based chemotherapy. The evolving landscape of TET treatments is marked by significant advancements in targeted therapies and immunotherapies, particularly with anti-angiogenic agents and immune checkpoint inhibitors (ICIs). While monotherapies demonstrated certain efficacy, the development of combination strategies is vital for improving patient outcomes. This review consolidates progress in anti-angiogenic therapies and ICIs, emphasizing the evolution of combination therapies of TETs. Furtherly, we particularly discuss new first-line strategies based on these advancements and emphasizes exploring novel treatments like antibody-drug conjugates, immunomodulatory drugs and cytokine-based agents for TETs. Mechanistically, the molecular features of TETs integrated with clinical diagnosis and targeted therapy, and immunophenotyping of TETs along with its impact on the efficacy and safety of immunotherapy are discussed. Thus, this review systemizes the development in the treatment landscape of TETs, integrating the corresponding molecular and immune mechanisms, aiming to provide new references for the treatment of TETs.

Non-Mutational Key Features in the Biology of Thymomas

Thymomas (THs) are a unique group of heterogeneous tumors of the thymic epithelium. In particular, the subtypes B2 and B3 tend to be aggressive and metastatic. Radical tumor resection remains the only curative option for localized tumors, while more advanced THs require multimodal treatment. Deep sequencing analyses have failed to identify known oncogenic driver mutations in TH, with the notable exception of the GTF2I mutation, which occurs predominantly in type A and AB THs. However, there are multiple alternative non-mutational mechanisms (e.g., perturbed thymic developmental programs, metabolism, non-coding RNA networks) that control cellular behavior and tumorigenesis through the deregulation of critical molecular pathways. Here, we attempted to show how the results of studies investigating such alternative mechanisms could be integrated into a current model of TH biology. This model could be used to focus ongoing research and therapeutic strategies.

What Have We Learned from Molecularly Informed Clinical Trials on Thymomas and Thymic Carcinomas-Current Status and Future Directions?

Thymic epithelial tumors (TETs), which include thymomas and thymic carcinomas, are a rare, heterogeneous group of malignancies that originate from the thymus gland. As an important organ of immune cell development, thymic tumors, particularly thymomas, are often associated with paraneoplastic autoimmune disorders. The advances in targeted therapies for both solid and hematologic malignancies have resulted in improved patient outcomes, including better and more durable efficacy and improved toxicity. Targeted therapies have also been investigated in the treatment of TETs, though the results have largely been modest. These have included somatostatin-receptor-targeting therapies, KIT- and EGFR-directed tyrosine kinase inhibitors, epigenetic modulators, anti-angiogenesis agents, and agents targeting the cell proliferation and survival pathways and cell cycle regulators. Numerous investigated treatments have failed or underperformed due to a lack of a strong biomarker of efficacy. Ongoing trials are attempting to expand on previous experiences, including the exploration of effective drugs in early-stage disease. Novel combination therapy strategies are also undergoing evaluation, with the goal of augmenting efficacy and understanding the toxicity while expanding the biomarkers of efficacy and safety. With advances in technology to improve target identification and drug delivery, old targets may become new opportunities, and the subsequently developed drugs may find their place in the treatment of thymic tumors.

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.

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.

GHSR methylation-dependent expression of a variant ligand and receptor of the ghrelin system induces thymoma tumorigenesis

Our previous study reported that the DNA methylation of growth hormone secretagogue receptor (GHSR) was significantly higher in thymoma or thymic carcinoma (TC) than in normal thymic tissue samples. Thymic epithelial tumors (TETs) with higher GHSR DNA methylation were associated with significantly worse prognosis than those with lower levels of DNA methylation. Diversified components of the ghrelin-GHSR axis may exert opposing effects in cancer progression, depending on the cancer type in question. However, the precise function of the axis remains unclear. In the present study, the mRNA expression of five key components of the ghrelin system [native ligand ghrelin, variant ligand In-1 ghrelin, native receptor GHSR1a, variant receptor GHSR1b and acylation enzyme ghrelin O-acyltransferase (GOAT)] were examined in 58 TET samples by reverse transcription-quantitative PCR, and protein expression of GHSR1a and GHSR1b was assessed in 20 TETs using immunohistochemistry. The results revealed that In-1 ghrelin, GHSR1b (variant forms) and GOAT were more strongly expressed in thymoma compared with thymic-adjacent tissue. By contrast, no significant differences were observed in the expression of ghrelin and GHSR1a (native forms) between thymoma and thymic tissue. The mRNA expression of In-1 ghrelin and GHSR1b (variant forms) was positively associated with GHSR methylation in thymoma tissue samples. However, a relationship was not found between ghrelin, GHSR1a or GOAT expression (native forms) and GHSR methylation in thymoma. Immunohistochemical analysis revealed that mRNA expression of GHSR1a and GHSR1b generally correlated with expression of the corresponding protein, and that the expression of GHSR1b was increased in advanced-stage TETs. These results indicate that the DNA methylation of GHSR is associated with a shift from native expression (ghrelin and GHSR1a) to variant expression (In-1 ghrelin and GHSR1b), which induces the tumorigenesis of thymoma, but not TC.

Molecular landscape of thymic epithelial tumors

Thymic epithelial tumors (TETs) are extremely rare and represent the most frequent tumors of the anterior mediastinum originating from epithelial cells in the thymus. Thymic epithelial tumors include thymomas (TM), thymic carcinomas (TC) and thymic neuroendocrine neoplasms (TNEN). Thymomas are the most predominant and are associated with autoimmune diseases. The available data suggests that the different histological subtypes have specific molecular alterations. Thymic carcinoma shows recurrent gene mutations, but further investigations are needed to understand the role of those mutations in the pathogenetic of the TETs. Some of the new emerging identified molecular alterations have the potential to offer new targeted therapies opening new possibilities for the treatment of thymic epithelial tumors.

An Overview on Molecular Characterization of Thymic Tumors: Old and New Targets for Clinical Advances

Thymic tumors are a group of rare mediastinal malignancies that include three different histological subtypes with completely different clinical behavior: the thymic carcinomas, the thymomas, and the rarest thymic neuroendocrine tumors. Nowadays, few therapeutic options are available for relapsed and refractory thymic tumors after a first-line platinum-based chemotherapy. In the last years, the deepening of knowledge on thymus' biological characterization has opened possibilities for new treatment options. Several clinical trials have been conducted, the majority with disappointing results mainly due to inaccurate patient selection, but recently some encouraging results have been presented. In this review, we summarize the molecular alterations observed in thymic tumors, underlying the great biological differences among the different histology, and the promising targeted therapies for the future.

The 100 most cited papers on thymic epithelial tumours: a bibliometric analysis

Bibliometric analysis can help us analyse the most influential papers, authors, research institutions in a discipline or topic and analyse the impact of these papers on a specific field. Our purpose is to identify the 100 most cited papers about thymic epithelial tumours (TETs) and analyse their key characteristics. We use certain search terms in the Web of Science database to identify the 100 most cited papers, and analysed the first author, country of the first author, institution, journal, type of paper, number of citations, and citation rate. The search returned 26,497 results. The top 100 papers received 17,674 citations. The most cited paper was by Masaoka et al. (n=1,190 citations), in which, clinical staging criteria are proposed for thymoma with special emphasis on the therapy and prognosis. The paper with the highest citation rate was also by Masaoka et al. (citations rate =30.51). Osaka University published the most papers (n=6) and accrued the highest number of citations (n=2,122 citations). The United States was the country with the most published papers (n=45) and the highest number of citations (n=7,991 citations). Cancer is the journal with the most published papers (n=19) and the highest number of citations (n=5,017 citations). Through the analysis of the most influential papers, this study provides a reference for researchers trying to understand TETs, thus providing guidance for future research.

Thymic Malignancy-Updates in Staging and Management

Thymomas are relatively indolent tumors that present with locally advanced disease in 30% of the patients. Thymic carcinoma is a more aggressive histology with shorter disease-free and overall survival. Early-stage tumors are managed best with complete resection. Multimodal therapy is the standard of care for locally advanced tumors and neoadjuvant therapy may help improve respectability. Stage and complete resection are the strongest prognostic factors for long-term survival. Based on early experience, targeted and immunotherapies have shown limited promise in advanced disease.

Diagnostic Roles of Immunohistochemistry in Thymic Tumors: Differentiation between Thymic Carcinoma and Thymoma

Background: The present study aims to evaluate the diagnostic roles of various immunohistochemical (IHC) markers in thymic tumors, including thymic carcinoma (TC) and thymoma (TM). Methods: Eligible studies were obtained by searching the PubMed databases and screening the searched articles. Thirty-eight articles were used in the present meta-analysis and included 636 TCs and 1861 TMs. Besides, for IHC markers with statistical significance, a diagnostic test accuracy review was performed. Results: The comparison of various IHC expressions between TC and TM was performed for 32 IHC markers. Among these IHC markers, there were significant differences between TC and TM for beta-5t, B-cell lymphoma 2 (Bcl-2), calretinin, CD1a, CD5, carcinoembryonic antigen (CEA), cytokeratin19 (CK19), CD117, glucose transporter 1 (Glut-1), insulin-like growth factor 1 receptor (IGF-1R), mesothelin, MOC31, mucin1 (MUC1), p21, and terminal deoxynucleotidyl transferase (TdT). Markers with higher expressions in TCs were Bcl-2, calretinin, CD5, CEA, CD117, Glut-1, IGF-1R, mesothelin, MOC31, MUC1, and p21. Among these markers, there were no significant differences between TC and TM type B3 in immunohistochemistries for Bcl-2 and CK19. On the other hand, β-catenin and CD205 showed a considerable difference in IHC expressions between TC and TM type B3, but not between TC and overall TM. In diagnostic test accuracy review, MUC1 and beta-5t were the most useful markers for TC and TM, respectively. Conclusions: Taken together, our results showed that the expression rates for various IHC markers significantly differed between TC and TM. The IHC panel can be useful for differentiation from limited biopsied specimens in daily practice.

The role of targeted therapy in thymic carcinoma

Thymic carcinoma is a rare entity and can be distinguished from benign thymomas by their aggressive nature and poor prognosis. The National Comprehensive Cancer Network guidelines recommend resection followed by adjuvant platinum-based chemotherapy for resectable tumors. However, the outcomes for metastatic or relapsed thymic carcinomas are poor with no regimen showing a consistent benefit. Moreover, the relative rarity of these tumors makes clinical trials difficult. Molecular analysis of thymomas shows a high incidence of genetic mutations and targeted therapy holds promise. We will briefly outline and review the current role of targeted therapy in thymic cancer.

High expression level of SOX2 is significantly associated with shorter survival in patients with thymic epithelial tumors

OBJECTIVES

Thymic epithelial tumors (TET) are heterogenous tumors which are composed of thymoma (TM) and thymic carcinoma (TC). We attempted to determine differences in gene expression between TM and TC, and to determine the effect of such genes on the prognosis of patients with TET.

MATERIALS AND METHODS

Gene expression profiles of SOX2, OCT-4, IGF-1, IGF-1R and IR mRNA transcripts in tumor tissues of TM and TC were determined using real-time PCR (RT-PCR). We constructed tissue microarray with 140 paraffin-embedded tumor tissues and performed immunohistochemistry (IHC) for IGF-1R-related signaling molecules, including SOX2, IGF-1, IGF-1R and pAKT.

RESULTS

SOX2 mRNA expression was notably higher (216-fold) in TCs than in TMs. However, there was no significant difference in expression of IGF-1, IGF-1R, OCT-4 or IR between the two tumor types. In IHC results, SOX2 (HR: 7.57, P = 0.001) and IGF-1 (HR: 9.43, P = 0.001) expression levels in TC were significantly higher than those in TM. There was a significant correlation in expression of SOX2 with IGF-1 (P = 0.021) and pAKT (P = 0.026). In univariate analysis, clinical TNM stage, WHO classification, serum LDH, expression of SOX2, IGF-1R, IGF-1 and pAKT, were significantly correlated with overall survival (OS). Multivariate analysis using a forward-selection procedure revealed that clinical N stage (HR: 4.08, P < 0.001), M stage (HR: 3.37, P = 0.001) and SOX2 expression (HR: 4.53, P = 0.010) were significantly associated with OS.

CONCLUSIONS

SOX2 is expressed significantly higher in TC than in TM. SOX2 expression is also closely related to IGF-1 and pAKT expression. The higher expression of SOX2 is significantly associated with shorter survival in patients with TET.

CD52, CD22, CD26, EG5 and IGF-1R expression in thymic malignancies

BACKGROUND

Thymic epithelial tumours are rare cancers for which new treatment options are required. Identification of putative predictive markers is important for developing clinical trials. We studied the expression of five putative predictive biomarkers, potentially actionable by approved experimental drugs.

METHODS

CD52, CD22, CD26, EG5, and IGF-1R expression were investigated by immunohistochemistry in formalin-fixed surgical samples of thymic epithelial tumour patients. All samples containing 10% positive epithelial tumour cells, independent of tumour cell intensity, were considered as positive. Correlation with histological subtype was performed.

RESULTS

106 surgical samples (89 thymomas, 12 thymic carcinoma, and 5 thymic neuroendocrine tumours) were evaluated. Overall, CD52, CD22, CD26, EG5 and IGF-1R expression was observed in 7%, 42%, 25%, 42% and 77% of samples, respectively. CD52 expression was more frequent in B2 and B3 thymoma. All TET subtypes stained for CD22, mainly AB thymoma (68%). CD26 expression also correlated with AB thymoma (68%), and A thymoma (50%) subtype, while IGFR1 was the most common marker expressed by thymic carcinoma samples (92%), followed by EG5 (60%). Only EG5 expression was significantly higher in thymic carcinomas than in thymomas (75% vs. 38%, p=0.026).

CONCLUSIONS

Our data were consistent with a previous study of IGF-1R expression. Based on their expression, activity of agents targeting CD52, CD 22, CD26 and EG5 could be further explored in TET patients.

Induction Therapy for Thymoma

Thymomas are uncommon tumors that can present as locally advanced tumors in approximately 30% of the patients. Stage and complete resection are the strongest prognostic factors. For locally advanced tumors, induction treatment may improve the ability to achieve a complete resection. Combination treatment with cisplatin, doxorubicin, and cyclophosphamide is the most commonly used induction regimen. Similar rates of resectability are noted with the use of induction chemotherapy and chemoradiation therapy; however, more tumor necrosis is noted with the addition of radiation.

Preoperative induction therapy for locally advanced thymic tumors: a retrospective analysis using the ChART database

BACKGROUND

To evaluate the role of preoperative induction therapy on prognosis of locally advanced thymic malignancies.

METHODS

Between 1994 and 2012, patients received preoperative induction therapies (IT group) in the Chinese Alliance for Research in Thymomas (ChART) database, were compared with those having surgery directly after preoperative evaluation (DS group). All tumors receiving induction therapies were locally advanced (clinically stage III-IV) before treatment and those turned out to be in pathological stage I and II were considered downstaged by induction. Clinical pathological characteristics were retrospectively analyzed. To more accurately study the effect of induction therapies, stage IV patients were then excluded. Only stage I-III tumors in the IT group and stage III cases in the DS group were selected for further comparison in a subgroup analysis.

RESULTS

Only 68 (4%) out of 1,713 patients had induction therapies, with a R0 resection of 67.6%, 5-year recurrence of 44.9%, and 5- and 10-year overall survivals (OS) of 49.7% and 19.9%. Seventeen patients (25%) were downstaged after induction. Significantly more thymomas were downstaged than thymic carcinomas (38.7% vs. 13.9%, P=0.02). Tumors downstaged after induction had significantly higher 5-year OS than those not downstaged (93.8% vs. 35.6%, P=0.013). For the subgroup analysis when stage IV patients were excluded, 5-year OS was 85.2% in the DS group and 68.1% in the IT group (P=0.000), although R0 resection were similar (76.4% vs. 73.3%, P=0.63). However, 5-year OS in tumors downstaged after induction (93.8%) was similar to those in the DS group (85.2%, P=0.438), both significantly higher than those not downstaged after induction (35.6%, P=0.000).

CONCLUSIONS

Preoperative neoadjuvant therapy have been used only occasionally in locally advanced thymic malignances. Effective induction therapy leading to tumor downstaging may be beneficial for potentially unresectable diseases, especially in patients with thymomas. These findings would be helpful to related studies in the future.

Multidisciplinary management of thymic carcinoma

Thymic carcinomas represent approximately 10% of thymic tumors. In our approach to patients with thymic carcinoma, we emphasize multimodality treatment with close communication between the pathologist, thoracic surgeon, medical oncologist, and radiation oncologist. Given the paucity of high-quality clinical research data, treatment decisions are guided by a small amount of prospective trial data, retrospective reports, and clinical experience. Surgical management of thymic carcinoma must account for the more aggressive biology, higher degree of local invasion of neighboring structures, greater propensity for nodal metastasis, and higher risk of distant metastatic disease. Although surgical resection remains the most important component in the management of localized thymic tumors, radiation therapy (RT) may be used as adjuvant therapy after surgical resection or as the definitive treatment modality in patients who are deemed unresectable because of medical comorbidities or technical reasons. Systemic therapy for thymic carcinoma is used in two clinical scenarios: preoperative treatment and palliative therapy. First-line, platinum-based chemotherapy regimens are associated with response rates between 22% and 75%. Recent data from targeted therapy trials do not reveal a clear role for targeted therapies for patients with thymic carcinoma.

Targeted therapy for thymic epithelial tumors: a new horizon? Review of the literature and two cases reports

Surgical resection remains the cornerstone of therapy for early-stage thymic epithelial tumors (TETs), while in advanced or recurrent forms, a multimodality approach incorporating radiation and chemotherapy is required. Given the absence of effective treatment options for metastatic/refractory TETs and the poor related prognosis, there is a compelling need to identify promising 'drugable' molecular targets. Initial reports of activity from targeted agents in TETs derived from anecdotal cases have been often associated with specific activating mutations. Only in recent years, several agents have been formally investigated into prospective clinical trials, with varying success rates. We reviewed the literature on targeted therapy in TETs along with two cases of thymoma achieving striking responses to sorafenib in combination with lapatinib.

Thymoma and thymic carcinomas

Thymomas (Ts) and thymic carcinomas (TCs) are rare tumours of the mediastinum with an incidence rate of 1.7/million per year in Europe. Histological classification is based on rate of non-malignant-appearing thymic epithelial cells and proportions of lymphocytes (A, AB, B1, B2, B3, and C), while staging system concerns localisation of the involved areas. Surgery is the mainstay of treatment with a 10-year survival of 80%, 78%, 75%, and 42% for stages I, II, III and IV, respectively, with an R0 resection. Radiotherapy has a role in selected cases (stage III patients or R1-2 residual) and platinum-based chemotherapy remains the standard of care for patients with advanced disease. A multimodality approach would be advisable when surgery is not recommended. Since molecular aberrations are poorly understood and few responses are reported, targeted therapies are yet being studied. In this review, we describe key aspects of clinical management for Ts and TCs.

FDG PET/CT Manifestation of Rare Widespread Metastatic Chemoradiation-Refractory Thymic Squamous Cell Carcinoma

A 74-year-old man underwent excisional biopsy of an anterior mediastinal mass that revealed squamous cell carcinoma of thymic origin. Immunohistochemistry revealed insulin-like growth factor-1 receptor positivity, which has been associated with worse prognosis. Restaging FDG PET/CT revealed extensive soft tissue and osseous metastases despite surgery and chemoradiation therapy. Patient was then enrolled in a clinical trial with anti-insulin-like growth factor-1 receptor therapy. A 3-month follow-up FDG PET/CT showed disease progression with an increase in size and number of hypermetabolic metastatic lesions, including interval development of multiple new metastases.

State of the art of genetic alterations in thymic epithelial tumors

The rapid advent of technology in recent years has resulted in a substantial increase in our knowledge of the molecular underpinnings of thymic epithelial tumors. In addition to previously described chromosomal aberrations and alterations in DNA methylation, genome sequencing has helped unravel hitherto unknown mutations in these tumors. Attempts are also being made to develop gene signatures to help in the identification of patients likely to benefit from adjuvant therapy. Some of the recently identified genetic alterations have the potential to serve as targets for biological therapy, thus opening newer avenues for treatment of thymic epithelial tumors and increasing the number of effective options for treatment of recurrent or refractory disease.

Available evidence and new biological perspectives on medical treatment of advanced thymic epithelial tumors

Thymic epithelial tumors (TETs) are rare primary mediastinal tumors arising from thymic epithelium. Their rarity and complexity hinder investigations of their causes and therapy development. Here, we summarize the existing knowledge regarding medical treatment of these tumors, and thoroughly review the known genetic aberrations associated with TETs and the present status of potential biological treatments. Epidermal growth factor receptor (EGFR), stem-cell factor receptor, insulin-like growth factor-1 receptor (IGF1R), and vascular endothelial growth factors (VEGF-A, VEGF-B, and VEGF-2) are overexpressed in TETs. EGFR overexpression in TETs is associated with higher stage, and IGF1R overexpression has poor prognostic value. Data indicate that anti-IGF1R monoclonal antibodies, and inhibitors of angiogenesis, somatostatin receptors, histone deacetylase, mammalian target of rapamycin, and cyclin-dependent kinases may be active against TETs. Continued investigations in this field could lead to advancement of targeted and biological therapies for TETs.

Response to cytotoxic chemotherapy in patients previously treated with palliative-intent chemotherapy for advanced thymic carcinoma

BACKGROUND

Clinical efficacy of second- and later-line chemotherapy for patients with thymic carcinoma previously treated with chemotherapy remains uncertain; limited data are available about this carcinoma because of its rarity. The aim of this study was to investigate effective chemotherapy for patients with thymic carcinoma previously treated with chemotherapy using a retrospective analysis of responses and times to event.

PATIENTS AND METHODS

We conducted a retrospective review of the medical records of 23 advanced thymic carcinoma patients previously treated with palliative-intent chemotherapy between 1980 and 2014 in our institution. Clinical demographic characteristics, agents, response, and time to treatment failure for each treatment line and overall survival were reviewed. Factors expected to be associated with survival rates were analyzed. Differences in survival were assessed using Kaplan-Meier analysis and univariate and multivariate Cox proportional hazards regression analyses.

RESULTS

The study included 13 men (56.5%) and 10 women (43.5%). The median age at diagnosis was 58.5 years. The most common histological subtypes were squamous cell carcinoma (16 patients [69.6%]), followed by neuroendocrine carcinoma (4 patients [17.4%]). The objective response rates of first-, second-, third-, and fourth-line chemotherapy were 60.9%, 39.1%, 23.1%, and 25.0%, respectively. The median survival time was 18.8 months (95% confidence interval, 7.5-40.9 months). Uni- and multivariate analyses of all assessed variables failed to identify any statistically significant indicators of overall survival.

CONCLUSION

Patients with thymic carcinoma previously treated with palliative-intent chemotherapy might respond to second- or later-lines of cytotoxic chemotherapy.

[Research status of molecular targeted therapy in thymic epithelial tumors]

In recent years, as the study of molecular mechanism and signal transduction pathways of tumors, molecular target therapy in many solid tumors has made great progress. At present, more and more studies focus on molecular target drugs in thymic epithelial tumors and people have got some experience. Molecular target therapy may be a new therapeutic option for patients of thymic epithelial tumor.

Systemic treatment of advanced thymic malignancies

The rarity of thymic malignancies prevents us from performing large randomized clinical trials. As a result, systemic treatment decisions are often guided by a small amount of prospective trial data, retrospective series, and individual case reports. In recent years, we have begun to unravel the molecular biology of thymic tumors. It is becoming more apparent as a result of gene expression profiling and genomic clustering studies that the subclassifications of type A, AB, B1, B2, B3, and thymic carcinoma have different molecular features that may be clinically relevant. Genomic profiling distinguishes type B3 thymoma and thymic carcinoma as distinct entities from type A and type B2 thymoma. Furthermore, type B2 thymomas can be separated from other subgroups in that it has a more distinct lymphocytic component than the other groups where epithelial cells predominate. Next generation RNA sequencing has recently identified a large microRNA cluster on chromosome 19q13.42 in types A and AB thymomas, which is absent in type B thymomas and thymic carcinomas. This cluster has been shown to result in activation of the phosphoinositide 3-kinase (PI3K)/AKT pathway, which suggests a possible role for PI3K inhibitors in these subtypes. The presence of KIT mutations in thymic carcinomas is also well described. Herein we discuss the chemotherapeutic and targeted treatment options for advanced thymic malignancies and highlight important advances in our understanding of the molecular biology of these rare tumors.

Methylation and expression profiles of MGMT gene in thymic epithelial tumors

OBJECTIVES

A key challenge in diagnosis and treatment of thymic epithelial tumors (TET) is in improving our understanding of the genetic and epigenetic changes of these relatively rare tumors.

METHODS

Methylation specific PCR (MSP) and immunohistochemistry were applied to 66 TET to profile the methylation status of DNA repair gene O6-methylguanine DNA methyltransferase (MGMT) and its protein expression in TET to clarify the association between MGMT status and clinicopathological features, response to chemotherapy and overall survival.

RESULTS

MGMT methylation was significantly more frequent in thymic carcinoma than in thymoma (17/23, 74% versus 13/44, 29%; P<0.001). Loss of expression of MGMT protein was significantly more frequent in thymic carcinoma than in thymoma (20/23, 87% versus 10/44, 23%; P<0.0001). There is a significant correlation between of MGMT methylation and loss of its protein expression (P<0.0003). MGMT methylation and loss of expression were significantly more frequent in advanced thymic epithelial tumors (III/IV) than in early tumors (I/II).

CONCLUSION

MGMT methylation plays a soul role in development of TET, especially in thymic carcinoma. Therefore, translation of our results from basic molecular research to clinical practice may have important implication for considering MGMT methylation as a marker and a target of future therapies in TET.

Thymic neoplasms: an update on the use of chemotherapy and new targeted therapies. A literature review

Thymic malignancies represent a wide range of clinical, histological and molecular entities, with probably considerable heterogeneity even among tumors of the same histotype. Systemic chemotherapy with cisplatin-based regimens continues to represent the standard of care in metastatic or inoperable refractory/recurrent diseases and ADOC regimen (including cisplatin, doxorubicin, vincristine and cyclophosphamide) demonstrated the longer overall response rate and median survival in the first line setting, although no randomized trial is available; and there is still a lack of standard treatment after first-line failure. To date research efforts are focused on translational studies on molecular pathways involved in thymic tumors carcinogenesis, aimed to better understand and predict the efficacy of chemotherapy and targeted therapy. Recent molecular characterization includes identification of a number of oncogenes, tumor suppressor genes, chromosomal aberrations, angiogenic factors, and tumor invasion factors involved in cellular survival and proliferation and in tumor growth. The use of biologic drugs is currently not recommended in a routine practice because there are limited data on their therapeutic role in thymic epitelial tumors. Because of the lack of data from adequate-sized, prospective trials are required for validation and the enrolment of patients with advanced disease into available clinical trials has to be encouraged.

FDG PET-CT aids in the preoperative assessment of patients with newly diagnosed thymic epithelial malignancies

INTRODUCTION

Advanced thymoma (stage III and IV) is difficult to detect by computed tomography (CT), yet it is important to distinguish between early (stage I and II) and advanced disease before surgery, as patients with locally advanced tumors require neoadjuvant chemotherapy to enable effective resection. This study assessed whether the amount of fluorodeoxyglucose (FDG) uptake can predict advanced thymoma and whether it can separate thymoma from thymic cancer.

METHODS

We retrospectively reviewed FDG positron emission tomography (PET)-CT scans of 51 consecutive newly diagnosed patients with thymic epithelial malignancy. PET-CT findings documented focal FDG activity: SUVmax, SUVmean, SUVpeak, and total body volumetric standardized uptake value (SUV) measurements. These were correlated with Masaoka-Koga staging and World Health Organization classification. Wilcoxon ranked sum tests were used to assess association between SUV and pathological stage, cancer type, and classification.

RESULTS

Among the study patients, 37 had thymoma, 12 thymic carcinoma, and 2 thymic carcinoid. Higher focal FDG uptake was seen in patients with type B3 thymoma than in those with type A, AB, B1, or B2 thymoma (p < 0.006). FDG uptake was higher in patients with thymic carcinoma or carcinoid than in patients with thymoma (p < 0.0003), with more variable associations with volumetric SUV measurements. There was no significant association observed between higher focal FDG uptake and advanced-stage disease in thymoma patients (p > 0.09), although greater FDG-avid tumor volume was significantly associated with advanced disease (p < 0.03).

CONCLUSIONS

Focal FDG uptake cannot predict advanced thymoma but is helpful in distinguishing thymoma from thymic carcinoma, or the more aggressive thymoma, type B3.

Messenger RNA and protein expression of thymidylate synthase and DNA repair genes in thymic tumors

BACKGROUND

Thymic epithelial tumors include several entities with different biologic behavior. Chemotherapy is indicated in advanced disease, but limited data exist on gene expression correlation with the response to chemotherapeutic agents.

PATIENTS AND METHODS

A series of 69 thymic neoplasms (7 A-, 6 AB-, 6 B1-, 10 B2-, 14 B3-thymomas, 22 carcinomas and 4 combined tumors) was collected to assess gene expression of thymidylate synthase (TS), excision repair cross complementing-1 (ERCC1), ribonucleotide reductase subunit 1 (RRM1), topoisomerase 2α (TOP2A) and mTOR.

RESULTS

A strong linear correlation between TS gene and protein expression was observed (P<0.0001, R=0.40). TS expression was significantly lower in pure A-thymomas and thymic carcinomas (P<0.0001) and progressively decreasing from B1-type to thymic carcinomas (B1>B2>B3>C; P<0.0001). RRM1 and TOP2A mRNA expression levels were significantly correlated with TS levels (both P=0.03) with a similar trend of expression among histotypes. RRM1 and TOP2A high levels were significantly correlated with high TS (P=0.03) and low tumor stages (I-II) (P<0.0001 and P<0.01, respectively). No relevant changes of ERCC1 and mTOR were detected.

CONCLUSIONS

Low TS and, to a minor extent, RRM1 and TOP2A expression were detected in aggressive thymic tumors. These findings should be prospectively considered in selecting the most appropriate chemotherapy.

Protein expression and gene copy number changes of receptor tyrosine kinase in thymomas and thymic carcinomas

BACKGROUND

Insulin-like growth factor-1 receptor (IGF-1R), epidermal growth factor receptor (EGFR), human epidermal growth factor receptor-type 2 (HER2), and c-Met are members of the receptor tyrosine kinases (RTKs). The associations between the RTK status [protein expression and gene copy number (GCN)] and patient characteristics and between the RTK status and prognosis remain undetermined.

MATERIALS AND METHODS

The study included 140 patients who underwent surgery for thymic tumors. Protein expression was evaluated by immunohistochemistry (IHC) and GCN was evaluated by bright-field in situ hybridization (BISH). The correlations between the RTK status and clinicopathological findings were examined.

RESULTS

IGF-1R protein was frequently detected in thymic carcinoma (83.8%) and EGFR in thymic tumors (91.4%). Thirty-six and 39 tumors were BISH high for IGF-1R and EGFR, respectively: 28 and 25 exhibited high polysomy; 8 and 14 exhibited gene amplification. No tumor was positive for HER2 or c-Met by IHC and BISH. Multivariate analysis revealed that IGF-1R gene amplification (P = 0.027), thymic carcinoma histology, and higher tumor stage were significantly correlated with an adverse prognosis.

CONCLUSIONS

Thymic epithelial tumors frequently express IGF-1R and/or EGFR proteins. IGF-1R gene amplification is suggested to define an unfavorable subset for thymic epithelial tumors.

Molecular aspects of thymic carcinoma

Thymic carcinomas are tumors of the anterior mediastinum derived from the epithelial cells of the thymic gland. Due to their low incidence they are often investigated in combination with thymomas under the rubric of "thymic epithelial neoplasms" and studies exclusively addressing thymic carcinomas are sparse. Thymic carcinomas are characterized by their histologic variability, often resembling tumors seen in other organ systems. This morphologic variation coupled with their rarity has prevented large scale research of these tumors and little is known about the etiology, biologic behavior or best treatment for thymic carcinoma. In recent years, attempts have been made to investigate the molecular characteristics of these tumors in the hope that molecular profiling can be used to predict the prognosis or lead to the development of new treatment strategies. Herein we provide an overview of the recent advances of the molecular analysis of thymic carcinoma with particular emphasis on the potential use for molecularly targeted therapies.

Immunohistochemical analysis of thymic carcinoma focusing on the possibility of molecular targeted and hormonal therapies

OBJECTIVE

Thymic carcinoma is a rare mediastinal malignant tumor, and in many patients, the tumor is detected in an inoperable advanced stage. Even when chemotherapy is administered to such patients, the patients show a poor response. We investigated new biomarkers of therapeutic molecular targets.

METHODS

This study included 44 patients diagnosed and treated for primary thymic epithelial tumors at Showa University Northern Yokohama Hospital, Showa University Hospital, and Showa University Fujigaoka Hospital from 2003 to 2011. We investigated new biomarkers of therapeutic molecular targets, such as the peroxisome proliferator-activated receptor γ (PPARγ), insulin-like growth factor 1 receptor (IGF1R), epidermal growth factor receptor (EGFR), estrogen receptor (ER), progesterone receptor (PgR), androgen receptor (AR), human epidermal growth factor type 2 (HER2)/neu, CD44, and L-type amino acid transporter 1 (LAT1), in thymic tumors.

RESULT

Immunohistochemical analysis showed that the PPARγ positivity rate in thymic carcinoma was 32 %, which was significantly higher than that in thymoma (4 %). The IGF1R positivity rate in thymic carcinoma was 73 %, which was significantly higher than that in thymoma (27 %).

CONCLUSION

Therefore, by examining the expressions of PPARγ and IGF1R, it would be possible to identify therapy-responsive patients and to improve results of thymic carcinoma treatment.

Thymoma: from chemotherapy to targeted therapy

Thymic malignancies are rare epithelial tumors that may be aggressive and difficult to treat. Thymomas are frequently eligible for upfront surgical resection. However, nearly 30% of patients present with locally advanced tumor at time of diagnosis, and chemotherapy is then used to reduce the tumor burden-possibly allowing subsequent surgery and/or radiotherapy. Metastatic and recurrent thymic malignancies may be similarly treated with chemotherapy. More recently, the molecular characterization of thymoma led to the identification of potentially druggable targets, laying the foundation to implement personalized medicine for patients.

Thymic malignancies: from clinical management to targeted therapies

PURPOSE

A key challenge in the treatment of thymoma and thymic carcinoma (TC) is in improving our understanding of the molecular biology of these relatively rare tumors. In recent years, significant efforts have been made to dissect the molecular pathways involved in their carcinogenesis. Here we discuss the results of large-scale genomic analyses conducted to date and review the most active chemotherapies and targeted treatments.

METHODS

We reviewed the literature for chemotherapeutic trials in the last 20 years and trials involving targeted therapies between 1999 and 2010. The search was supplemented by a review of abstracts presented at the annual meetings of the American Society of Clinical Oncology (from 1999 to 2010), at the first International Conference on Thymic Malignancies in 2009, and at a follow-up meeting of the newly formed International Thymic Malignancies Interest Group in 2010.

RESULTS

Surgery remains the treatment of choice for operable tumors, whereas chemotherapy is standard in locally advanced and metastatic disease. Thus far, targeted therapies have been developed empirically. Histone deacetylase inhibitors have shown some activity in thymoma whereas sunitinib may be active in TC. There are no data to support the use of HER2- or EGFR-targeted therapies in thymic malignancies.

CONCLUSION

Drug development for the treatment of thymic malignancies is difficult because of the rarity of these tumors. Ethnic differences are becoming apparent, with aggressive subtypes being observed in Asians and African Americans. Incremental improvements in our understanding of tumor biology suggest that molecular profiling-directed therapies may be the preferred route of investigation in the future.

IGF-1R expression predicts clinical outcome in patients with locally advanced oral squamous cell carcinoma

To assess the expression of IGF-1R in oral cavity squamous cell carcinoma patients, to explore its relation with clinical and pathologic prognostic factors and its role in predicting clinical outcome. One hundred and thirty-one consecutive patients suffering from oral cavity squamous cell carcinoma were included in this study from July 1989 to April 2005. Follow-up was closed in May 2010. The mean follow-up for survivors was 110.26±47.42 months. Patients were staged following the TNM classification. Patients in tumour stages I and II were referred to surgery. Patients in stages III-IV were referred to postoperative radiotherapy. Radiation therapy was administered up to a mean dose of 62.13±7.74 Gy in 1.8-2 Gy fractions. IGF-1R expression was studied by immunohistochemistry in paraffin-embedded tumour tissue. IGF-1R was expressed in 101 patients (77.1%). IGF-1R expression was related to tumour grade (P=0.012). Tumour stage was the most important prognostic factor for survival. Low (negative and fairly) IGF-1R tumour expression was correlated to better long-term Local Disease Free Survival (P=0.016), Disease-Free Survival (P=0.029), and Survival (P=0.009) in patients achieving tumour stages III-IV. Low IGF-1R expression was related to better long-term control in patients suffering locally advanced oral carcinoma.

Thymic tumors: relevant molecular data in the clinic

INTRODUCTION

Thymic malignancies are rare intrathoracic tumors that may be aggressive and difficult to treat in advanced stage. Over the past years, significant efforts have been conducted to dissect the molecular pathways involved in the carcinogenesis of these tumors. Insights have been made following anecdotal clinical responses to targeted therapies, and large-scale genomic analyses have been conducted.

METHODS

Review of the literature, 1990-2010.

RESULTS

The Epidermal Growth Factor Receptor (EGFR) is frequently overexpressed in thymomas and thymic carcinomas, but EGFR mutations are exceptional, and this does not support the use of EGFR tyrosine kinase inhibitors. On the contrary, single observations of responses create a basis for further evaluation of cetuximab in thymomas. KIT-mutant thymic carcinomas represent a small molecular subset of thymic tumors. The clinical relevance of KIT mutations is more limited in thymic carcinoma than in GIST as KIT mutations are far less frequent (7% of thymic carcinomas) and are not correlated with KIT expression; furthermore, KIT mutants are not uniformly sensitive to imatinib. Beyond EGFR and KIT signaling pathways, other molecular alterations with potential prognostic or predictive relevance are emerging in thymic malignancies.

CONCLUSIONS

Given the rarity of these tumors, translation of preclinical findings to the clinic may be quick and represents one of the most promising therapeutic approaches for advanced-stage thymic malignancies.