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

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.

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.

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.

Receptor tyrosine kinase (c-Kit) inhibitors: a potential therapeutic target in cancer cells

c-Kit, a receptor tyrosine kinase, is involved in intracellular signaling, and the mutated form of c-Kit plays a crucial role in occurrence of some cancers. The function of c-Kit has led to the concept that inhibiting c-Kit kinase activity can be a target for cancer therapy. The promising results of inhibition of c-Kit for treatment of cancers have been observed in some cancers such as gastrointestinal stromal tumor, acute myeloid leukemia, melanoma, and other tumors, and these results have encouraged attempts toward improvement of using c-Kit as a capable target for cancer therapy. This paper presents the findings of previous studies regarding c-Kit as a receptor tyrosine kinase and an oncogene, as well as its gene targets and signaling pathways in normal and cancer cells. The c-Kit gene location, protein structure, and the role of c-Kit in normal cell have been discussed. Comprehending the molecular mechanism underlying c-Kit-mediated tumorogenesis is consequently essential and may lead to the identification of future novel drug targets. The potential mechanisms by which c-Kit induces cellular transformation have been described. This study aims to elucidate the function of c-Kit for future cancer therapy. In addition, it has c-Kit inhibitor drug properties and their functions have been listed in tables and demonstrated in schematic pictures. This review also has collected previous studies that targeted c-Kit as a novel strategy for cancer therapy. This paper further emphasizes the advantages of this approach, as well as the limitations that must be addressed in the future. Finally, although c-Kit is an attractive target for cancer therapy, based on the outcomes of treatment of patients with c-Kit inhibitors, it is unlikely that Kit inhibitors alone can lead to cure. It seems that c-Kit mutations alone are not sufficient for tumorogenesis, but do play a crucial role in cancer occurrence.

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.

c-kit mutation-positive advanced thymic carcinoma successfully treated as a mediastinal gastrointestinal stromal tumor: A case report

Thymic carcinoma is an exceptionally rare tumor, which has a very poor prognosis, differing from thymoma. Although cytotoxic chemotherapy is commonly used to treat advanced thymic carcinoma, its effectiveness has not been found to be sufficient. There are several reports that thymic carcinoma also harbors an oncogenic driver mutation, similar to lung cancer. A patient with a c-kit mutation-positive thymic carcinoma received imatinib followed by sunitinib consecutively, which are both c-Kit inhibitors. Although the patient had achieved long-term disease control for 21 months, the primary lesion and pulmonary metastases had increased in size by November, 2014. Following failure of imatinib treatment, the patient received sunitinib, a multiple kinase inhibitor, initiated in December, 2014. Following administration of sunitinib, a computed tomography scan revealed a partial response and the disease was effectively controlled with continued sunitinib treatment for 6 months, up to June, 2015. The patient achieved long-term disease control (~27 months) with imatinib followed by sunitinib. The efficacy of consecutive molecular-targeted therapy for thymic carcinoma was demonstrated in this case. Therefore, thymic carcinoma with oncogenic driver mutations should be treated with molecular-targeted agents rather than with cytotoxic drugs, and it may be suitable to treat c-kit mutation-positive thymic carcinoma as a mediastinal gastrointestinal stromal tumor.

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.

[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.

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.

Identification of novel mutations of TP53, ALK and RET gene in metastatic thymic squamous cell carcinoma and its therapeutic implication

Thymic tumors are epithelial tumors of the thymus for which multimodal therapies are often ineffective because of a lack of standardized regimens. Due to the low incidence, the molecular pathology and genomic abnormalities of thymic epithelial tumors are largely unknown. In this study, we report our comprehensively genomic study on a case of metastatic thymic tumor. Using next generation deep DNA sequencing technology, we sequenced 190 segments of 46 cancer genes of the cancer genome to cover 739 COSMIC mutations in 604 loci. Among these sequenced cancer genes, we identified that three low frequency (~10% of cells) mutations in the TP53 gene (c.782+1G>T), ALK gene (c.3551C>T), and RET gene (c.2651A>T). To the best of our knowledge, this is the first study to show those mutations in thymic tumor. Of note, our study further indicates comprehensive molecular analysis may facilitate development of novel diagnostic and therapeutic strategies for thymic tumors.

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.

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.