Malignant transformation of thymoma in recipient rats by heterotopic thymus transplantation from HTLV-I transgenic rats

Genetic characterization of thymoma

Thymoma represents the most common anterior mediastinal compartment neoplasm, originating from the epithelial cell population in the thymus. Various histological types of thymoma feature different clinical characteristics. Furthermore, thymoma is frequently associated with autoimmune disorders, esp. myasthenia gravis (MG). However, the underlying molecular tumourigenesis of thymoma remains largely unknown. The goal of our current study is to demonstrate the underlying genetic abberations in thymoma, so as to understand the possible cause of MG in thymoma patients. By using CapitalBio mRNA microarray analysis, we analyzed 31 cases of thymoma including 5 cases of type AB thymoma, 6 B1-type cases, 12 B2-type cases, 5 B2B3-type cases and 3 type-B3 cases. 6 cases of thymoma were not associated with myasthenia gravis, while 25 cases were with myasthenia gravis. By comparisons between thymoma and the paratumoral tissues, differentially expressed genes were identified preliminarily. Among them, 292 genes increased more than 2-fold, 2 genes more than 5-fold. On the other hand, 596 genes were decreased more than 2-fold, 6 genes more than 20-fold. Interestingly, among these genes upregulated more than 2-fold, 6 driver genes (FANCI, NCAPD3, NCAPG, OXCT1, EPHA1 and MCM2) were formerly reported as driver oncogenes. This microarray results were further confirmed through real-time PCR. 8 most dysregulated genes were verified: E2F2, EPHA1, CCL25 and MCM2 were upregulated; and IL6, FABP4, CD36 and MYOC were downregulated. Supervised clustering heat map analysis of 2-fold upregulated and 2-fold downregulated genes revealed 6 distinct clusters. Strikingly, we found that cluster 1 was composed of two type-B2 thymoma; and cluster 6 was three type-B2/B3 thymoma. KEGG database analysis revealed possible genetic mechanisms of thymoma and functional process. We further compared gene expression pattern between thymoma with and without MG, and found 5 genes were upregulated more than 2-fold, more than 30 genes were downregulated more than 2-fold. KEGG analysis revealed 2 important signaling pathways with more than 2-fold upregulated genes (TGF- beta signaling pathway and HTLV-I signaling pathway) as differially functioning between MG positive and negative thymomas. Real-time PCR analysis confirmed that CCL25 was upregulated; and MYC, GADD45B, TNFRSF12 downregulated in thymoma with MG. Our study thus provided important genetic information on thymoma. It shed light on the molecular bases for analyzing the functional process of thymoma and finding potential biomarkers for pathological categorizing and treatment. Our work may provide important clues in understanding possible causes of MG in thymoma patients.

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.

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.

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.

CD4+/CD8+ macrophages infiltrating at inflammatory sites: a population of monocytes/macrophages with a cytotoxic phenotype

We found a population of nonlymphoid cells expressing both CD4 and CD8 in peripheral blood mononuclear cells (PBMCs) of human T-cell leukemia virus type-I pX transgenic rats with autoimmune diseases. These cells, which showed a monocytic phenotype, were also found in wild-type rats, and their number increased by adjuvant-assisted immunization. GM-CSF increased the number of these double-positive (DP) monocytes in PBMCs. Consistent with the idea that DP monocytes differentiate into DP macrophages at sites of inflammation, we found infiltration of DP macrophages at the site of myosin-induced myocarditis in wild-type rats; these cells exhibited a T-helper 1 (Th1)-type cytokine/chemokine profile and expressed high levels of Fas ligand, perforin, granzyme B, and NKR-P2 (rat orthologue of human NKG2D). Adoptive transfer of GFP-positive spleen cells confirmed hematogenous origin of DP macrophages. DP monocytes had a cytotoxic phenotype similar to DP macrophages, indicating that this phenotypic specialization occurred before entry into a tissue. In line with this, DP monocytes killed tumor cells in vitro. Combined evidence indicates that certain inflammatory stimuli that induce GM-CSF trigger the expansion of a population of DP monocytes with a cytotoxic phenotype and that these cells differentiate into macrophages at inflammatory sites. Interestingly, human PBMCs also contain DP monocytes.