Long lasting response to the multikinase inhibitor bay 43-9006 (Sorafenib) in a heavily pretreated metastatic thymic carcinoma

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.

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.

An Overview of the Use of Anti-Angiogenic Agents in the Treatment of Thymic Epithelial Tumors

Angiogenesis significantly influences the carcinogenesis of thymic epithelial tumors (TET). Both thymomas and thymic carcinoma (TC) overexpress VEGF-A and VEGFR-1 and -2. This review aims to provide an appraisal of the use of anti-angiogenics in the treatment of TET. The literature research identified 16 studies that were deemed eligible for further analysis. Seven studies assessed the clinical efficacy of sunitinib and five studies the use of apatinib and/or anlotinib. The multicenter Japanese phase II REMORA trial investigated the efficacy of lenvatinib, which is a multi-targeted inhibitor of VEGFR, FGFR, RET, c-Kit, and other kinases. The objective response rate was 38% (25.6-52%), which is the highest documented in TET that progressed after first-line chemotherapy. Anti-angiogenic agents may be useful in the treatment of TET, which are not amenable to curative treatment. Their toxicity profile seems to be acceptable. However, angiogenesis inhibitors do not appear to have a major influence on either thymomas or TC, although multikinase inhibitors may have some effect on TC. The current evidence suggests that the most active agent is lenvatinib, whereas sunitinib could be proposed as an acceptable second-line therapy for TC. Further research concerning the combination of immune checkpoint inhibitors with anti-angiogenic drugs is warranted.

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.

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.

Targeted Next-Generation Sequencing of Thymic Epithelial Tumours Revealed Pathogenic Variants in KIT, ERBB2, KRAS, and TP53 in 30% of Thymic Carcinomas

A better understanding of the molecular pathogenesis of thymic epithelial tumours (TETs) could revolutionise their treatment. We evaluated thymomas and thymic carcinomas by next-generation sequencing (NGS) of somatic or germline single nucleotide variants (SNVs) in genes commonly mutated in solid tumours. In total, 19 thymomas and 34 thymic carcinomas were analysed for nonsynonymous SNVs in 15 genes by targeted NGS (reference genome: hg19/GRCh37). Ten SNVs in TP53 (G154V, R158P, L194H, R267fs, R273C, R306 *, Q317 *), ERBB2 (V773M), KIT (L576P), and KRAS (Q61L) considered somatic and pathogenic/likely pathogenic were detected in 10 of 34 (29.4%) thymic carcinomas. No somatic SNVs confirmed as pathogenic/likely pathogenic were found in thymomas. Rare SNVs of uncertain or unknown functional and clinical significance, to our knowledge not reported previously in TETs, were found in ERBB2 (S703R), KIT (I690V), and FOXL2 (P157S) in 3 of 19 (16%) thymomas. The most frequent germline SNVs were TP53 P72R (94% TETs), ERBB2 I655V (40% TETs), and KIT M541L (9% TETs). No significant difference in median disease-free survival (DFS) was found between thymic carcinoma patients with and without pathogenic SNVs (p = 0.190); however, a trend toward a longer DFS was observed in the latter (16.0 vs. 30.0 months, respectively). In summary, NGS analysis of TETs revealed several SNVs in genes related to the p53, AKT, MAPK, and K-Ras signalling pathways. Thymic carcinomas showed greater genetic dysregulation than thymomas. The germline and rare SNVs of uncertain clinical significance reported in this study add to the number of known genetic alterations in TETs, thus extending our molecular understanding of these neoplasms. Druggable KIT alterations in thymic carcinomas have potential as therapeutic targets.

Apatinib in patients with recurrent or metastatic thymic epithelial tumor: a single-arm, multicenter, open-label, phase II trial

BACKGROUND

Thymic epithelial tumors (TETs) are rare malignancies and the treatment options are limited. We aimed to evaluate the efficacy and safety of apatinib, an angiogenesis inhibitor, in advanced TETs.

METHODS

This was an open-label, single-arm, phase II trial at three centers in China. Patients with TET who had progressed after failure of at least one line of platinum-based chemotherapy were enrolled. Patients received apatinib 500 mg orally per day. The primary endpoint was objective response rate (ORR). Secondary endpoints were progression-free survival (PFS), overall survival (OS), disease control rate (DCR), and safety.

RESULTS

From June 29, 2017, to April 18, 2019, 25 patients were enrolled. At data cut off (September 30, 2021), one patient achieved complete response, nine achieved partial response, and 11 achieved stable disease, with an ORR of 40% (95% CI 21-61%) and DCR of 84% (95% CI 64-95%). The median PFS was 9.0 (95% CI 5.4-12.6) months. The median OS was 24.0 (95% CI 8.2-39.8) months. All patients reported treatment-related adverse events (TRAEs). Grade 3 TRAEs occurred 26 times in 15 patients. No grade 4 or 5 toxicities occurred.

CONCLUSIONS

This is the first trial of apatinib for the treatment of TETs. Apatinib showed promising antitumor activity and the toxicities were tolerable and manageable.

Therapeutic options in thymomas and thymic carcinomas

INTRODUCTION

Radical surgery is the best therapeutic option for thymic malignancies. However, patients with advanced or recurrent thymic malignancies often require chemotherapy or radiotherapy. Since thymic malignancies are rare cancers, the efficacy and safety of treatments have been verified based on small Phase 2 trials or retrospective studies.

AREA COVERED

We comprehensively reviewed the treatment strategies for thymic malignancies, including surgery, radiotherapy, and pharmacotherapy, including cytotoxic chemotherapy, molecular-targeted therapy, and immunotherapy. Additionally, we reviewed specific situations, such as pleural dissemination, central nervous system metastasis, and paraneoplastic syndrome.

EXPERT OPINION

Cytotoxic chemotherapy remains the standard option in pharmacotherapy. However, multikinase inhibitors, such as sunitinib and lenvatinib, and immune checkpoint inhibitors including pembrolizumab have been developed to treat thymic carcinomas. Now, a Phase 2 study is evaluating whether lenvatinib plus pembrolizumab benefits patients with type B3 thymoma or thymic carcinoma. Phosphatidylinositol 3-kinase/AKT/ mammalian target of rapamycin inhibitors may contribute to disease control and octreotide scan is only applicable to somatostatin analogues. Although the genomic characteristics of thymic malignancies have been analyzed, few actionable mutations have been detected in general. The development of a treatment strategy using combination pharmacotherapy is anticipated.

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.

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.

Genomic alterations in thymoma-molecular pathogenesis?

Thymomas and thymic carcinomas (TCs) are neoplasms of thymic epithelial cells. Thymomas exhibit a low mutational burden and a few recurrently mutated genes. The most frequent missense mutation p.(Leu404His) affects the general transcription factor IIi (GTF2I) and is specific for thymic epithelial tumors (TETs). The clinically indolent types A and AB thymomas express the miRNA cluster C19MC. This miRNA cluster known to be the largest in the human genome, is-with expression otherwise restricted mostly to embryonal tissue-silenced in the more aggressive type B thymomas and TCs. Thymomas associated with the autoimmune disease myasthenia gravis (MG) exhibit more frequent gene copy number changes and an increased expression of proteins homologous to molecules that are targets for autoantibodies. TCs, however, display a higher mutational burden, with frequent mutations of TP53 and epigenetic regulatory genes and loss of CDKN2A. The knowledge of molecular alterations in TETs fosters the understanding of their pathogenesis and provides guidance for further studies that may lead to the development of targeted therapies.

Lenvatinib in patients with advanced or metastatic thymic carcinoma (REMORA): a multicentre, phase 2 trial

BACKGROUND

Thymic carcinoma is a rare malignant disease and standard treatment for advanced or metastatic thymic carcinoma previously treated with platinum-based chemotherapy has not been established. Lenvatinib is a novel multi-targeted inhibitor of VEGFR, FGFR, RET, c-Kit, and other kinases. The aim of this trial was to assess the activity and safety of lenvatinib as a second-line treatment in thymic carcinoma.

METHODS

This single-arm, phase 2 trial done in eight institutions in Japan (five cancer centres, two medical university hospitals, and one public hospital) enrolled patients with pathologically confirmed unresectable advanced or metastatic thymic carcinoma that progressed following at least one platinum-based chemotherapy. Key inclusion criteria were age 20 years or older, at least one measurable lesion as defined by the Response Evaluation Criteria in Solid Tumors version 1.1, and an Eastern Cooperative Oncology Group performance status of 0 or 1. Patients received 24 mg of lenvatinib orally once daily in 4-week cycles until disease progression or occurrence of unacceptable adverse events. The primary endpoint was objective response rate evaluated at the data cutoff date (Feb 22, 2019), by independent central review in the intention-to-treat population. This trial is registered on JMACCT, JMA-IIA00285, and on UMIN-CTR, UMIN000026777.

FINDINGS

Between April 21, 2017, and Feb 22, 2018, 42 patients were enrolled and all patients were included in the activity and safety analysis. The median follow-up period was 15·5 months (IQR 13·1-17·5). The objective response rate was 38% (90% CI 25·6-52·0, p<0·0001). 16 (38%) of 42 patients had a partial response and 24 (57%) had stable disease. The most frequent grade 3 treatment-related adverse events were hypertension (27 [64%]) and palmar-plantar erythrodysaesthesia syndrome (three [7%]). No patient died from adverse events.

INTERPRETATION

The activity and safety of lenvatinib in patients with advanced or metastatic thymic carcinoma was confirmed. These results suggest that lenvatinib could become a standard treatment option for patients with previously treated advanced or metastatic thymic carcinoma.

FUNDING

Center for Clinical Trials, Japan Medical Association.

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.

Analysis of a panel of druggable gene mutations and of ALK and PD-L1 expression in a series of thymic epithelial tumors (TETs)

INTRODUCTION

Thymic epithelial tumors (TETs) are rare neoplasms with different prognosis lacking consistent molecular alterations possibly leading to targeted therapy. We collected a consecutive series of TETs aimed at investigating the mutational status of druggable genes (EGFR, c-KIT, KRAS, BRAF, PDGFR-alpha and -beta, HER2 and c-MET) and the expression of ALK and PD-L1.

PATIENTS AND METHODS

One hundred twelve consecutive cases of TETs and relative clinico-pathologic features were collected. Immunohistochemical expression of ALK (clone D5F3) and PD-L1 (clone E1L3N), molecular analysis of EGFR (exons 18-21), c-KIT (exons 9,11,13,14,17), KRAS (exon 2), BRAF (exon 15), PDGFR-alpha (exon 12) and -beta (exons 12, 14, 18), HER-2 (exons 19 and 20) and c-MET (exons 14, 17, 18, 19) mutations were performed. Immuno-molecular results were then statistically matched with clinico-pathologic characteristics.

RESULTS

Patients were male in 54% of cases, with a median age of 61 years (range 19-83) and affected mainly by thymoma (78%) in stage II (45%). At molecular analysis, there were 4 c-KIT mutations (occurring in exon 11 V559A, L576P, Y553N and exon 17 D820E) in thymic carcinomas (typeC), but not in other tumor types (p=0.003). No mutations were detected in other genes and none case was ALK positive. Twenty-nine (26%) cases were PD-L1 positive (65% of thymic carcinomas and 18% of thymomas). High PD-L1 expression was statistically associated with WHO classification stage type C (p<0.001) and Masaoka stage III-IV disease (p=0.007). In univariate analysis, WHO classification type C, advanced Masaoka stage and absence of myasthenia, but not PD-L1 expressions were correlated with worse survival; at multivariate analysis, only WHO type C confirmed its negative prognostic role.

CONCLUSION

A subset of TETs as thymic carcinomas can harbor c-KIT mutations and elevated PD-L1 expression that could represent targets of potential therapeutic use.

Molecular Profiling of Thymoma and Thymic Carcinoma: Genetic Differences and Potential Novel Therapeutic Targets

Thymoma and thymic carcinoma are thymic epithelial tumors (TETs). We performed a molecular profiling to investigate the pathogenesis of TETs and identify novel targets for therapy. We analyzed 37 thymomas (18 type A, 19 type B3) and 35 thymic carcinomas. The sequencing of 50 genes detected nonsynonymous mutations in 16 carcinomas affecting ALK, ATM, CDKN2A, ERBB4, FGFR3, KIT, NRAS and TP53. Only two B3 thymomas had a mutation in noncoding regions of the SMARCB1 and STK11 gene respectively. Three type A thymomas harbored a nonsynonymous HRAS mutation. Fluorescence in situ hybridization detected in 38 % of carcinomas a CDKN2A, in 32 % a TP53 and in 8 % an ATM gene deletion, whereas only one B3 thymoma exhibited a CDKNA deletion, and none of the type A thymomas showed a gene loss. Sequencing of the total miRNA pool of 5 type A thymomas and 5 thymic carcinomas identified the C19MC miRNA cluster as highly expressed in type A thymomas, but completely silenced in thymic carcinomas. Furthermore, the miRNA cluster C14MC was downregulated in thymic carcinomas. Among non-clustered miRNAs, the upregulation of miR-21, miR-9-3 and miR-375 and the downregulation of miR-34b, miR-34c, miR-130a and miR-195 in thymic carcinomas were most significant. The expression of ALK, HER2, HER3, MET, phospho-mTOR, p16^INK4A, PDGFRA, PDGFRB, PD-L1, PTEN and ROS1 was investigated by immunohistochemistry. PDGFRA was increased in thymic carcinomas and PD-L1 in B3 thymomas and thymic carcinomas. In summary, our results reveal genetic differences between thymomas and thymic carcinomas and suggest potential novel targets for therapy.

Mutation analysis of the EGFR gene and its downstream signaling pathway in thymic carcinoma patients from a Chinese Han population

INTRODUCTION

For thymic carcinoma (TC), which is a rare epithelial neoplasm of the thymus gland, median survival with current treatments is only 2 years.

OBJECTIVES

Mutations in the epidermal growth factor receptor (EGFR) gene or its downstream effectors may cause constitutive activation that leads to cell proliferation and metastases. Thus, molecular profiling is essential for selecting TC patients who may respond to anti-EGFR therapies.

METHODS

Genomic DNA was extracted from 61 histological samples of TCs. Real-time polymerase chain reaction (PCR) and direct sequencing were used to assess the mutations in the EGFR downstream pathway.

RESULTS

Gene mutations were identified in seven patients (11.5%). In particular, the identified mutations included four mutations in the KRAS gene, one mutation in the BRAF gene, one mutation in the PIK3CA gene, and only one mutation in the EGFR gene itself. Gene mutations in the EGFR downstream pathway were associated with shorter survival time and were observed to be an independent prognostic factor for TC patients.

CONCLUSION

Mutations in the EGFR downstream pathway are not rare in TCs. These data offer interesting possibilities for the future management of TCs, particularly in the era of new targeted therapies.

Rare frequency of gene variation and survival analysis in thymic epithelial tumors

Objective

Thymic epithelial tumor (TET) is a rare mediastinal neoplasm and little is known about its genetic variability and prognostic factors. This study investigated the genetic variability and prognostic factors of TET.

Patients and methods

We sequenced 22 cancer-related hotspot genes in TET tissues and matched normal tissues using Ampliseq Ion Torrent next-generation technology. Overall survival was evaluated using Kaplan–Meier methods and compared with log-rank tests.

Results

A histological analysis of 52 patients with a median age of 52 years showed 15 patients (28.8%) with thymic carcinoma, five with type A thymoma (9.6%), eight with type AB (15.4%), six with type B1 (11.5%), nine with type B2 (17.3%), and nine with type B3 thymoma (17.3%). Three gene mutations were identified, including two with PIK3CA mutation and one with EGFR mutation. The three patients with mutant genes included two cases of thymoma (one with EGFR and the other with PIK3CA mutation) in addition to a case of thymic carcinoma (PIK3CA mutation). The 5-year survival rates were 77.7% in all patients. The 5-year survival rates were 93.3%, 90.0%, 76.9%, and 22.9% corresponding to Masaoka stages I, II, III, and IV (P<0.001). The 5-year survival rates were 100%, 100%, 83.3%, 88.9%, 65.6%, and 60.9% in the histological subtypes of A, AB, B1, B2, and B3 thymomas, and thymic carcinoma, respectively (P=0.012).

Conclusion

Hotspot gene mutations are rare in TET. PIK3CA and EGFR mutations represent candidate driver genes and treatment targets in TET. Masaoka stage and histological subtypes predict the survival of TET.

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.

Stereotactic ablative radiotherapy with CyberKnife for advanced thymic carcinoma: a case report

Thymic carcinoma is a rare but lethal mediastinal cancer. The optimal treatment for advanced thymic carcinoma is not yet established. This report is the first known of stereotactic ablative radiotherapy (sabr) with CyberKnife (Accuray, Sunnyvale, CA, U.S.A.) as definitive therapy for thymic carcinoma. The patient, a 70-year-old woman with thymic carcinoma, invasion into neighboring organs, and pleural metastases-underwent CyberKnife sabr at 40 Gy in 5 fractions for two lesions, one in the thymus and one in the right paraspinal pleura. After 61 months of observation, a partial response was observed in the irradiated fields. However, disease progression in the non-irradiated pleura was noted. The patient underwent salvage CyberKnife sabr for the four initially nonirradiated pleural lesions. Computed tomography images obtained 10 months after the salvage therapy revealed a partial response. The patient is living, with progression-free irradiated lesions and no radiation-related toxicity. CyberKnife sabr is feasible for patients who are unable to undergo either surgery or conventionally fractionated radiation therapy.

Response to nab-paclitaxel and nedaplatin in a heavily-metastatic thymic carcinoma: A case report

Metastatic thymic carcinoma is an aggressive cancer that usually responds poorly to multimodal therapies. Although surgical resection is the preferred treatment for patients with advanced or metastatic disease, the clinical prognosis is typically poor. The present study describes a 63-year-old patient with thymic carcinoma who underwent a range of antitumor treatments, including surgical resection, post-operative radiotherapy and post-operative chemotherapy with several drugs, but ultimately responded to treatment with nab-paclitaxel (nab-P) and nedaplatin. Subsequent to six cycles of nab-P and nedaplatin, the lung and peritoneal metastases decreased in size and the pleural effusion was reduced. To the best of our knowledge, this is the first study to describe the response of an advanced thymic carcinoma to nab-P chemotherapy.

Do thymic malignancies respond to target therapies?

A best evidence topic in cardiothoracic surgery was written according to a structured protocol. The question addressed was 'Do thymic malignancies respond to target therapies?' Altogether, 347 papers were found using the reported search, of which, in our opinion, 16 papers represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers were tabulated. We did not find any randomized controlled trials on target therapies for the thymic malignancies, due to the very small incidence of this tumour, and it seems unlikely that there will be any such trials in the foreseeable future. Three studies on target therapies showed that several cases of thymic malignancies were reported to have partial response (PR) to epidermal growth factor receptor tyrosine kinase inhibitors such as cetuximab and erlotinib, whereas, one study on erlotinib and another on gefitinib showed no activity. Proto-oncogene c-KIT (KIT) mutant thymic carcinomas were noted to benefit from target therapies, implying that systematic sequencing of KIT in thymic carcinoma tumours may be warranted for optimal patient selection. A study that investigated the efficacy of cixutumumab, a fully human IgG1 monoclonal antibody that binds to insulin-like growth factor 1 receptor, indicated that relapsed thymomas tended to respond, whereas thymic carcinoma did not. The antiangiogenesis agent belinostat had modest antitumour activity in heavily pretreated thymoma, but no response to thymic carcinoma was found. Several cases with metastatic thymic carcinoma showed that multitargeted kinase inhibitors, such as sunitinib and sorafenib, were effective. We concluded that, as the side-effects of the agents were tolerable in almost all reported cases, target therapies can be an option for patients with heavily pretreated thymoma.

Sunitinib in patients with chemotherapy-refractory thymoma and thymic carcinoma: an open-label phase 2 trial

BACKGROUND

No standard treatments are available for advanced thymic epithelial tumours after failure of platinum-based chemotherapy. We investigated the activity of sunitinib, an orally administered tyrosine kinase inhibitor.

METHODS

Between May 15, 2012, and Oct 2, 2013, we did an open-label phase 2 trial in patients with histologically confirmed chemotherapy-refractory thymic epithelial tumours. Patients were eligible if they had disease progression after at least one previous regimen of platinum-containing chemotherapy, an Eastern Cooperative Oncology Group performance status of two or lower, measurable disease, and adequate organ function. Patients received 50 mg of sunitinib orally once a day, in 6-week cycles (ie, 4 weeks of treatment followed by 2 weeks without treatment), until tumour progression or unacceptable toxic effects arose. The primary endpoint was investigator-assessed best tumour response at any point, which we analysed separately in thymoma and thymic carcinoma cohorts. Patients who had received at least one cycle of treatment and had their disease reassessed were included in the analyses of response. The trial was registered with ClinicalTrials.gov, number NCT01621568.

FINDINGS

41 patients were enrolled, 25 with thymic carcinoma and 16 with thymoma. One patient with thymic carcinoma was deemed ineligible after enrolment and did not receive protocol treatment. Of patients who received treatment, one individual with thymic carcinoma was not assessable because she died. Median follow-up on trial was 17 months (IQR 14.0-18.4). Of 23 assessable patients with thymic carcinoma, six (26%, 90% CI 12.1-45.3, 95% CI 10.2-48.4) had partial responses, 15 (65%, 95% CI 42.7-83.6) achieved stable disease, and two (9%, 1.1-28.0) had progressive disease. Of 16 patients with thymoma, one (6%, 95% CI 0.2-30.2) had a partial response, 12 (75%, 47.6-92.7) had stable disease, and three (19%, 4.1-45.7) had progressive disease. The most common grade 3 and 4 treatment-related adverse events were lymphocytopenia (eight [20%] of 40 patients), fatigue (eight [20%]), and oral mucositis (eight [20%]). Five (13%) patients had decreases in left-ventricular ejection fraction, of which three (8%) were grade 3 events. Three (8%) patients died during treatment, including one individual who died of cardiac arrest that was possibly treatment-related.

INTERPRETATION

Sunitinib is active in previously treated patients with thymic carcinoma. Further studies are needed to identify potential biomarkers of activity.

FUNDING

National Cancer Institute (Cancer Therapy Evaluation Program).

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.

Antitumor activity of sorafenib and imatinib in a patient with thymic carcinoma harboring c-KIT exon 13 missense mutation K642E

We report the case of a man with an advanced nonkeratinizing squamous cell thymic carcinoma harboring c-KIT exon 13 missense mutation K642E. This aberration is rare and has never been described previously in patients with thymic cancers. It has been found in a small number of cases of gastrointestinal stromal tumor and also in several cases of acral and mucosal melanomas. Some of the patients with gastrointestinal stromal tumor or melanoma harboring this rare mutation have had a tumor response when treated with imatinib. In contrast, in our case, the mutation was associated with primary resistance to full doses of imatinib but, at the same time, it was not a cause of resistance to sorafenib.

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.

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.

When a thymic carcinoma "becomes" a GIST

Thymic carcinoma (TC) is a rare intrathoracic malignancy that it can be invasive and refractory to conventional treatment. Comprehensive genomic analysis evidenced a molecularly distinct subset of thymic carcinoma with high prevalence of c-kit mutation, which may behave as a gastrointestinal stromal tumor (GIST). Here, we present a case report of TC with c-Kit mutation, who has relapsed after exposure to multiple lines of combination chemotherapy, but he has shown an impressive and long lasting response to sunitinib after imatinib failure.

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.

Long lasting efficacy of sorafenib in a heavily pretreated patient with thymic carcinoma

Thymoma and thymic carcinoma are rare neoplasms of the mediastinum, arising from the epithelial cells of the thymus. While surgical resection is the treatment of choice in early stages, platin-based chemotherapy is mainly used in patients with advanced or metastatic disease; however, the prognosis is poor. Here we present the case of a 54 year old female patient suffering from a CD117-negative thymic carcinoma with widespread metastases. After several courses of different kinds of chemotherapy, finally these approaches failed to be effective. Thus we initiated a treatment with sorafenib, an inhibitor of several receptor tyrosine kinases. The treatment was tolerated very well, and within a few weeks the general condition of the patient improved significantly. A CT-scan, performed 3 months after therapy with sorafenib started, showed a 50 % reduction of tumor size, and this effect lasted for 15 months. When the carcinoma relapsed again, we administered another course of chemotherapy and, because of lacking success, we even tried to use sunitinib. However, the patient died in a septic shock, based on progressive disease. In summary, we present a patient with metastastic thymic carcinoma, in which sorafenib led to a tumor-control for 18 months.

Emerging treatment options for patients with recurrent advanced thymic epithelial tumors

The purpose of this review article is to review recent advances in the treatment of advanced thymic epithelial tumors. These tumors are generally responsive to cytotoxic combination chemotherapy in the first-line setting. While newer agents have shown efficacy in the salvage setting, there is no one standard approach. A multitude of targeted agents have shown promise generally in case reports, though as of yet, nothing has shown consistent benefit. Because of the rarity of thymic epithelial tumors, clinical trial enrollment is difficult but nevertheless essential.

Activating c-KIT mutations in a subset of thymic carcinoma and response to different c-KIT inhibitors

BACKGROUND

To analyze a multi-institutional series of type C thymic carcinomas (TCs) (including neuroendocrine tumors), focusing on the expression and mutations of c-KIT.

MATERIALS AND METHODS

Immunohistochemical expression of c-KIT/CD117, p63, CD5 and neuroendocrine markers, as well as mutational analysis of c-KIT exons 9, 11, 13, 14, 17 by direct sequencing of 48 cases of TCs. Immunohistochemical and molecular data were statistically crossed with clinicopathological features.

RESULTS

Overall, 29 tumors (60%) expressed CD117, 69% were positive for CD5 and 85% (41 cases) for p63. Neuroendocrine markers stained all six atypical carcinoids and five poorly-differentiated thymic squamous cell carcinomas. Overall, six CD117-positive cases (12.5%) showed c-KIT mutation. No mutation was detected in CD117-negative tumors and carcinoids. All the mutations were found in poorly-differentiated thymic squamous cell carcinomas expressing CD117, CD5, p63 and lacking neuroendocrine markers (6 of 12 cases with these features). Mutations involved exon 11 (four cases: V559A, L576P, Y553N, W557R), exon 9 (E490K) and exon 17 (D820E).

CONCLUSIONS

All TCs need an immunohistochemical screening with CD117, while c-KIT mutation analysis is mandatory only in CD117-positive cases, particularly when coexpressing CD5 and p63, lacking neuroendocrine differentiation. The finding of c-KIT mutation can predict efficacy with different c-KIT inhibitors.

HER family receptor and ligand status in thymic carcinoma

Overexpression and gene amplification of the HER family of receptors and their ligands are important prognostic factors in many solid tumors and treatment targeting these molecules has recently become available. The role of this group of receptors has only rarely been described in thymic epithelial neoplasms and never before in a series of cases consisting exclusively of thymic carcinoma. Twenty-four primary squamous cell carcinomas of the thymus were examined for immunohistochemical expression of epidermal growth factor receptor (EGFR), phosphorylated EGFR (pEGFR), HER2, phosphorylated HER2 (pHER2), HER3, phosphorylated HER3 (pHER3) and their ligands epidermal growth factor (EGF), transforming growth factor-α (TGF-α), amphiregulin and epiregulin. Fluorescence in situ hybridization (FISH) analysis for amplification of the EGFR and HER2 genes was performed including assessment of the copy numbers of EGFR and HER2 gene per cell and the ratio of EGFR and HER2 to centromere 7 and 17, respectively. Significant immunohistochemical expression was observed for EGFR (33.3%), pEGFR (33.3%), HER2 (58.3%), HER3 (45.8%), TGF-α (54.1%), amphiregulin (25.0%) and epiregulin (91.7%). A single case showed HER2 gene amplification by FISH. Increased EGFR and HER2 gene copy numbers were observed in 2 (8.4%) and 18 cases (75%), respectively. Eight cases (33.3%) showed an increased HER2:CEP17 ratio. The results of this study indicate that EGFR and HER2 amplification is a rare event in thymic carcinoma, however, protein expression for HER receptors as well as their ligands is a common finding indicating that targeted therapy directed against these molecules may be considered in the treatment of these tumors.

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.

Platelet-derived growth factor and platelet-derived growth factor receptor-α expression in the normal human thymus and thymoma

Platelet-derived growth factor (PDGF) and its receptors (PDGFRs) are strongly involved in the normal development of several organs, tumour angiogenesis and malignant progression and metastasis. Few studies concerning their expression, distribution and role in normal and pathological human thymus are available in the literature. The aim of this study has been to analyse the immunohistochemical expression of PDGF and PDGFR-α in prenatal and postnatal normal human thymus and thymomal biopsy specimens. The results demonstrated immunoreactivity to both PDGF and PDGFR-α in all specimens, but the intensity, distribution and number of positive cells were different in normal thymus and thymomas, and also among different tumour types. PDGF and PDGFR-α were weakly expressed in foetal and postnatal humans with a different distribution between cortex and medulla in both blood vessels and epithelial cells, whereas they were overexpressed in thymoma, especially in type B2 and B3, in the tumour epithelial cells. Overall, these data suggest that PDGF and PDGFR-α may be involved in the pathophysiology of the human thymus.

Promising efficacy of sorafenib in a relapsed thymic carcinoma with C-KIT exon 11 deletion mutation

Advanced thymic carcinoma (TC) is a very aggressive disease. To date there are no established treatment options for the refractory and recurrent disease and only a few prospective trials have been conducted in patients with TC. Here we present a case of a relapsed TC patient, who, by using combination chemotherapy, showed a positive response to sorafenib with C-KIT exon 11 mutation.