Occult pleural dissemination detected intraoperatively in patients with thymic tumors: a retrospective analysis

Background Thymic tumors usually present with adjacent organ invasion or pleural dissemination, but very few studies have reported on occult pleural dissemination detected intraoperatively. This study aimed to investigate the risk factors that can predict pleural dissemination preoperatively. Methods Consecutive patients with thymic tumors who underwent surgery from January 2010 to January 2017 were reviewed. Only patients without pleural dissemination detected preoperatively were included in this study. Demographic, clinical, pathological, and survival data were collected for statistical analysis. Further analyses were performed to find the risk factors of occult pleural dissemination. Results A total of 352 patients with thymic tumors were included in this study. Seven patients had pleural dissemination detected intraoperatively. All pleural dissemination cases were in clinical Masaoka-Koga stage III, and most underwent the video-assisted thoracoscopic surgery (VATS) approach (or VATS exploration). Univariate analysis showed that positive squamous cell carcinoma (SCC) antigen was the only predictor of pleural dissemination (p = 0.009). Tiny nodules close to the diaphragm were detected in the computed tomography scans of 1 case after reviewing the imaging data. Tumor recurrence occurred in 5 patients during follow-up. The disease-free survival rates were better in patients with a solitary nodule than those with multiple nodules (p = 0.019). No significant difference was detected in terms of disease-free survival rates between SCC antigen positive and SCC antigen negative patients. Conclusions Positive SCC antigen was the only detected risk factor for predicting pleural dissemination in thymic tumors preoperatively in this study. The VATS approach (including VATS exploration) is suggested for patients with clinical Masaoka-Koga stage III and SCC antigen positive thymic tumors, according to our experience.

Estimated Risk of Radiation-Induced Cancer after Thymoma Treatments with Proton- or X-ray Beams

We compared the calculated risks of radiation-induced secondary malignant neoplasms (SMNs) for patients treated for thymic tumors with 3D-CRT, IMRT, or single-field uniform dose (SFUD) proton beam therapy (PBT) using the pencil beam scanning (PBS) technique. A cancer-induction model based on the organ equivalent dose (OED) concept was used. For twelve patients, treated with 3D-CRT for thymic tumors, alternative IMRT and SFUD plans were retrospectively prepared. The resulting DVHs for organs at risk (OARs) were extracted and used to estimate the risk of SMNs. The OED was calculated using a mechanistic model for carcinoma induction. Two limit cases were considered; the linear-exponential model, in which the repopulation/repair of the cells is neglected, and the plateau model, in which full repopulation/repair of the irradiated cells is assumed. The calculated risks for SMNs for the different radiation modalities and dose-relation models were used to calculate relative risks, which were compared pairwise. The risks for developing SMNs were reduced for all OARs, and for both dose-relation models, if SFUD was used, compared to 3D-CRT and IMRT. In conclusion, PBS shows a potential benefit to reduce the risk of SMNs compared to 3D-CRT and IMRT in the treatment of thymic tumors.

Lymph Nodes Involvement and Lymphadenectomy in Thymic Tumors: Tentative Answers for Unsolved Questions

Thymic tumors are the most common primary neoplasms of the anterior mediastinum, although, when compared with the entire thoracic malignancies, they are still rare. Few studies addressed the questions about lymph node involvement pattern in thymic neoplasms, about which subgroup of patients would be appropriate candidates for lymph node dissection or about the extent of lymphadenectomy or which lymph nodes should be harvested. The aim of this review is to collect evidence from the literature to help physicians in designing the best surgical procedure when dealing with thymic malignancies. A literature review was performed through PubMed and Scopus in May 2021 to identify any study published in the last 20 years evaluating the frequency and the extent of lymph node dissection for thymic tumors, its impact on prognosis and on postoperative management. Fifteen studies met the inclusion criteria and were included in this review, with a total of 9452 patients with thymic cancers; lymph node metastases were found in 976 (10.3%) patients in total. The current literature is heterogeneous in the classification and reporting of lymph node metastases in thymic carcinoma, and data are hardly comparable. Surgical treatment should be guided by the few literature-based pieces of evidence and by the experience of the physicians.

METTL3-dependent MALAT1 delocalization drives c-Myc induction in thymic epithelial tumors

Background Thymic epithelial tumors (TETs) are rare neoplasms, originating from epithelial thymic cells. The oncogenic potential of these rare neoplasms is still largely undefined, and a deeper molecular characterization could result in a relevant advance in their management, greatly improving diagnosis, prognosis and treatment choice. Deregulation of N6-methyladenosine (m6A) RNA modification, catalyzed by the METTL3/METTL14 methyltransferase complex, is emerging as a relevant event in cell differentiation and carcinogenesis. Various studies have reported that altered expression of METTL3 is associated with an aggressive malignant phenotype and favors migration and invasiveness, but its role in Thymic Tumors remains unknown. Results In this study, we characterized that METTL3 contributes to Thymic Epithelial Tumor phenotype. We evidenced that METTL3 is overexpressed in tumor tissue compared to normal counterpart. Silencing of METTL3 expression in thymic carcinoma cells results in reduced cell proliferation and overall translation rate. Of note, METTL3 is responsible for the induction of c-MYC expression in TET cells. Specifically, high expression of c-MYC protein is enabled by lncRNA MALAT1, which is methylated and delocalized by METTL3. Interestingly, blocking of c-MYC by using JQ1 inhibitor cooperates with METTL3 depletion in the inhibition of proliferation and induction of cell death. Conclusion This study highlighted METTL3 as a tumor promoter in Thymic tumors and c-MYC as a promising target to be exploited for the treatment of TET.

Evaluation of Surgical Therapy in Advanced Thymic Tumors

A complete resection of thymic tumors is known to be the most important prognostic factor, but it is often difficult to perform, especially in advanced stages. In this study, 73 patients with advanced thymic tumors of UICC stages III and IV who underwent radical resection were examined retrospectively. The primary endpoint was defined as the postoperative resection status. Secondary endpoints included postoperative morbidity, mortality, recurrence/progression-free, and overall survival. In total, 31.5% of patients were assigned to stage IIIa, 9.6% to stage IIIb, 47.9% to stage IVa, and 11% to stage IVb. In stages III a R0 resection was achieved in 53.3% of patients. In stages IV a R0/R1 resection was documented in 76.7% of patients. Surgical revision was necessary in 17.8% of patients. In-hospital mortality was 2.7%. Median recurrence/progression-free interval was 43 months (p = 0.19) with an overall survival of 79 months. The 5-year survival rate was 61.3%, respectively. Median survival after R2 resection was 25 months, significantly shorter than after R0 or R1 resection (115 months; p = 0.004). Advanced thymic tumors can be resected with an acceptable risk of complications and low mortality. In stage III as well as in stage IV the promising survival rates are dependent on the resection-status.

Two Distinct Classes of Thymic Tumors in Patients with MEN1 Show LOH at the MEN1 Locus

Patients with the multiple endocrine neoplasia type 1 (MEN1) syndrome carry germline heterozygous loss-of-function mutations in the MEN1 gene which predisposes them to the development of various endocrine and non-endocrine tumors. Over 90% of these tumors have been shown to undergo biallelic inactivation of the MEN1 tumor suppressor gene by somatic loss of the wild-type allele resulting in loss of heterozygosity (LOH) at chromosome 11q13, the MEN1 gene locus. An uncommon manifestation of MEN1 is thymic neuroendocrine tumor (thymic NET), also referred to as thymic carcinoid, which in MEN1 patients is a major cause of mortality. In contrast to the other frequent NETs in MEN1 patients (pancreas, parathyroid, pituitary), LOH at the MEN1 locus has not been demonstrated in MEN1-associated thymic tumors. Therefore, it is generally thought that thymic tumor development in MEN1 patients is dependent on other somatic molecular events rather than a second hit to the MEN1 gene and its pathogenesis is largely unknown. The lack of knowledge of its pathogenesis limits the ability to explore therapies directed at this tumor, which is the most aggressive of all MEN1-associated tumors. The goal of this study was to investigate the molecular events contributing to thymic tumor development in our well-characterized cohort of MEN1 patients by evaluating LOH at the MEN1 locus and by utilizing transcriptomics to identify possible molecular hits that may lead to tumor development and could be considered for targeted therapy.

Advancement in Diagnostic Imaging of Thymic Tumors

Thymic tumors are rare neoplasms even if they are the most common primary neoplasm of the anterior mediastinum. In the era of advanced imaging modalities, such as functional MRI, dual-energy CT, perfusion CT and radiomics, it is possible to improve characterization of thymic epithelial tumors and other mediastinal tumors, assessment of tumor invasion into adjacent structures and detection of secondary lymph nodes and metastases. This review aims to illustrate the actual state of the art in diagnostic imaging of thymic lesions, describing imaging findings of thymoma and differential diagnosis.

Vascular Involvement in Thymic Epithelial Tumors: Surgical and Oncological Outcomes

Background: The involvement of mediastinal great vessels is common in advanced stage thymic tumors, which makes their surgical resection challenging. Moreover, the impact of vascular involvement on the oncological prognosis is still unclear. The aim of this study is to investigate the surgical and oncological outcomes and the impact of vascular involvement in a population of patients operated for advanced stage thymic tumors. Methods: A retrospective analysis on four hundred and sixty-five patients undergoing resection for advanced stage (Masaoka III–IV) thymic tumors in a single high-volume center was performed. One hundred forty-four patients met the inclusion criteria and were eligible for the study. Patients were divided in two groups according to the presence or absence of vascular involvement. Results: the two groups did not differ for the baseline characteristics and showed comparable surgical outcomes. Vascular involvement was not associated with worse overall survival but with an increased recurrence rate (p = 0.03). Multivariable analysis demonstrated a higher risk of recurrence in patients without R0 resection (HR 0.11, 0.02–0.54, p = 0.006) and with thymic carcinoma (HR 2.27, 1.22–4.24, p = 0.01). Conclusions: resection of thymic tumors with vascular involvement can be performed with optimal surgical results in a high volume center. From the oncological point of view, the involvement of the great vessels seems to be associated with a higher recurrence rate without affecting long-term survival.

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.