Thymic malignancies: emerging systemic therapies.

PURPOSE OF REVIEW: The management of thymic malignancies is based on multidisciplinary collaboration. Systemic agents may be administered as an exclusive treatment if local treatment is not achievable. Novel and innovative agents are needed. Integrated genomic analyses reported the activation of targetable signaling pathways in thymomas and thymic carcinomas. RECENT FINDINGS: Phase II trials reported the antitumor activity of phosphatidylinositol 3-kinase/mechanistic target of rapamycin kinase inhibitors, cyclin dependent kinase inhibitors, and antiangiogenic agents in advanced, refractory thymic malignancies. Meanwhile, a major challenge is the use of immune checkpoint inhibitors, given the frequent association of those tumors with autoimmune disorders. SUMMARY: Although those innovative agents were assessed in phase II trials reporting on variable antitumor efficacy in terms of response and survival, in selected and limited cohorts of patients, a better understanding of systemic treatment sequences in a real-life setting is mandatory to analyze the actual efficacy of each line of treatment one after another, define the best clinical-pathological selection of patients for the administration of chemotherapy, targeted agents, and immunotherapy, and develop individualized decision-making to optimize the survival of patients with advanced thymic malignancies.

A comparative study of the spatial distribution of mast cells and microvessels in the foetal, adult human thymus and thymoma.

Mast cells (MCs) are widely distributed in human and animal tissues and have been shown to play an important role in angiogenesis in normal and pathological conditions. Few data are available about the relationship between MCs and blood vessels in the normal human thymus, and there are virtually no data about their distribution and significance in thymoma. The aim of this study was to analyse the spatial distribution of MCs and microvessels in the normal foetal and adult thymus and thymoma. Twenty biopsy specimens of human thymus, including foetal and adult normal thymus and thymoma were analysed. Double staining with CD34 and mast cell tryptase was used to count both mast cells and microvessels in the same fields. Computer-assisted image analysis was performed to characterize the spatial distribution of MCs and blood vessels in selected specimens. Results demonstrated that MCs were localized exclusively to the medulla. Their number was significantly higher in thymoma specimens as compared with adult and foetal normal specimens respectively. In contrast the microvessel area was unchanged. The analysis of the spatial distribution and relationship between MCs and microvessels revealed that only in the thymoma specimens was there a significant spatial association between MCs and microvessels. Overall, these data suggest that MCs do not contribute significantly to the development of the vascular network in foetal and adult thymus, whereas in thymoma they show a close relationship to blood vessels. This could be an expression of their involvement not only in endothelial cells but also in tumour cell proliferation.

Angiogenesis in the human thymoma assessed by subclassification of tumor-associated blood vessels and endothelial cells proliferation.

The prognostic value of tumor-associated angiogenesis is still a subject of debate. As microvascular density and the expression of different growth factors were not demonstrated to be good predictors of the response to antiangiogenic and antivascular therapy, there is a strong need to search for more sensitive markers. In the present study we evaluated by double immunohistochemical staining the profile of tumor-associated blood vessels and the rate of endothelial cell proliferation in patients with thymoma (n=38). Results were compared with specimens of normal thymus and from patients with myasthenia gravis. We found a significant increase in the number of immature and intermediate blood vessels in the tumor area of thymoma, regardless the histological type of the tumor. Proliferating endothelial cells were found in 15 cases, and co-expression of Ki67 and CD34 had the highest value in immature vessels. Both blood vessel type and endothelial cell proliferation significantly correlated with invasive thymoma. Based on these findings, it can be assumed that the type of tumor-associated vessel together with endothelial cell proliferation are useful predictors of invasion, immature and intermediate vessels can be targeted with antivascular drugs and endothelial cell proliferation could be used as a good predictor of the response to antiangiogenic therapy.

Computed tomographic findings and prognosis in thymic epithelial tumor patients.

OBJECTIVE: To determine which computed tomographic findings are associated with high-risk thymic epithelial tumors and a poor prognosis. METHODS: Computed tomographic findings of thymic epithelial neoplasms were retrospectively evaluated in 75 patients diagnosed with thymic tumor between January 1997 and October 2003. We analyzed the correlation of the computed tomographic findings, histological subtype according to the World Health Organization classification, and the prognosis. RESULTS: There were 34 with type A approximately B1 tumor and 41 with type B2 approximately C tumor. On multiple regression analysis, vascular obliteration and a blunt sternum-anterior mediastinum angle were more frequent with thymic carcinoma than with thymoma. On multivariate analysis, pleural effusion and mediastinal fat infiltration on initial computed tomography had a significant impact on survival. CONCLUSIONS: Vascular obliteration and a blunt sternum-anterior mediastinum angle were predictive of thymic carcinoma. Pleural effusion and mediastinal fat infiltration were predictive of a poor prognosis.

Increased mast cell density and microvessel density in the thymus of patients with myasthenia gravis.

There were investigated 15 cases with normal thymus removed during cardiac surgery and nine cases with clinical signs of myasthenia gravis. Four patients with myasthenia gravis had thymoma (three invasive, one non-invasive). Specimens were fixed in buffer formalin, embedded in paraffin and slides were stained with Hematoxylin-Eosin and Alcian blue-Safranin. Additional slides were stained for factor VIII in order to estimate microvessel density. Mast cell density was performed at magnification x400, and microvessel density at magnification x200, using the "hot spot" method. There were found intralobular mast cells in all cases, located mainly in the cortex (6.53 in the normal thymus, 21.4 in patients with myasthenia gravis, and 10 in thymoma-associated myasthenia gravis). A significant increase in the number of intralobular mast cells was noticed in patients with myasthenia gravis without thymoma (p < 0.001), and a moderate increase in patients with thymoma-associated myasthenia gravis (p < 0.023). Values of microvessel density were 10.3 for the normal thymus, 33 for myasthenia gravis without thymoma and 21.8 for myasthenia gravis with associated thymoma. A strong correlation was found between the number of mast cells and microvessel densities in all three conditions.

Use of vasoactive agents to increase tumor perfusion and the antitumor efficacy of drug-monoclonal antibody conjugates.

The effects of both alpha 1- and beta-adrenergic blocking agents on the vascular perfusion of tumors were studied with the ultimate goal of improving diagnosis and therapy of solid tumors with the use of monoclonal antibody (MAb) conjugates. With the use of a subcutaneously growing murine thymoma, it was demonstrated that nonselective and cardioselective beta-adrenergic blocking agents were capable of increasing threefold tumor-to-blood and tumor-to-liver perfusion of 125I-labeled MAbs. Subsequently, these beta-adrenergic blocking agents were found to increase the antitumor efficacy of idarubicin (Ida)-MAb conjugates. Conjugate-treated mice that also received beta-adrenergic blocking agents had a smaller mean tumor size and a greater number of regressions than mice receiving Ida-MAb conjugate alone. By contrast, prazosin HCl, an alpha 1-adrenergic blocking agent, and Cyclospasmol, a peripheral vasodilator, did not enhance the tumor perfusion and antitumor efficacy of 125I- or Ida-conjugated MAbs, and no vasoactive agent enhanced the antitumor effect of Ida when used alone. By their selective action on normal blood vessels, vasoactive drugs can change the tumor-to-normal tissue perfusion ratio, thereby enhancing the access of drug-MAb conjugates to tumors and increasing the effectiveness of tumor therapy with the use of drug-MAb conjugates.

Vascular attack by 5,6-dimethylxanthenone-4-acetic acid combined with B7.1 (CD80)-mediated immunotherapy overcomes immune resistance and leads to the eradication of large tumors and multiple tumor foci.

The promise of cancer immunotherapy is that it will not only eradicate primary tumors but will generate systemic antitumor immunity capable of destroying distant metastases. A major problem that must first be surmounted relates to the immune resistance of large tumors. Here we reveal that immune resistance can be overcome by combining immunotherapy with a concerted attack on the tumor vasculature. The functionally related antitumor drugs 5,6-dimethylxanthenone-4-acetic acid (DMXAA) and flavone acetic acid (FAA), which cause tumor vasculature collapse and tumor necrosis, were used to attack the tumor vasculature, whereas the T-cell costimulator B7.1 (CD80), which costimulates T-cell proliferation via the CD28 pathway, was used to stimulate antitumor immunity. The injection of cDNA (60-180 microg) encoding B7.1 into large EL-4 tumors (0.8 cm in diameter) established in C57BL/6 mice, followed 24 h later by i.p. administration of either DMXAA (25 mg/kg) or FAA (300 mg/kg), resulted in complete tumor eradication within 2-6 weeks. In contrast, monotherapies were ineffective. Both vascular attack and B7.1 immunotherapy led to up-regulation of heat shock protein 70 on stressed and dying tumor cells, potentially augmenting immunotherapy. Remarkably, large tumors took on the appearance of a wound that rapidly ameliorated, leaving perfectly healed skin. Combined therapy was mediated by CD8+ T cells and natural killer cells, accompanied by heightened and prolonged antitumor cytolytic activity (P < 0.001), and by a marked increase in tumor cell apoptosis. Cured animals completely rejected a challenge of 1 x 10(7) parental EL-4 tumor cells but not a challenge of 1 x 10(4) Lewis lung carcinoma cells, demonstrating that antitumor immunity was tumor specific. Adoptive transfer of 2 x 10(8) splenocytes from treated mice into recipients bearing established (0.8 cm in diameter) tumors resulted in rapid and complete tumor rejection within 3 weeks. Although DMXAA and B7.1 monotherapies are complicated by a narrow range of effective doses, combined therapy was less dosage dependent. Thus, a broad range of amounts of B7.1 cDNA were effective in combination with 25 mg/kg DMXAA. In contrast, DMXAA, which has a very narrow range of high active doses, was effective at a low dose (18 mg/kg) when administered with a large amount (180 microg) of B7.1 cDNA. Importantly, combinational therapy generated heightened antitumor immunity, such that gene transfer of B7.1 into one tumor, followed by systemic DMXAA treatment, led to the complete rejection of multiple untreated tumor nodules established in the opposing flank. These findings have important implications for the future direction and utility of cancer immunotherapies aimed at harnessing patients' immune responses to their own tumors.

The LIM-domain protein Lmo2 is a key regulator of tumour angiogenesis: a new anti-angiogenesis drug target.

The growth of solid tumours requires a blood supply provided by re-modeling of existing blood vessel endothelium (angiogenesis). Little is known about transcription regulators which are specific for the control of tumour angiogenesis. The proto-oncogene LMO2 encodes a LIM domain transcription regulator which controls angiogenesis during mouse embryogenesis where it regulates remodelling of the capillary network into mature vessels. We now show that Lmo2 expression is augmented in tumour endothelium such as mouse thymomas and human lung tumours. The functional significance of this Lmo2 expression was assessed in teratocarcinomas induced in nude mice by subcutaneous implantation of Lmo2-lacZ targeted ES cells. CD31-positive, sprouting endothelium of ES-cell origin occurred in teratocarcinomas from heterozygous Lmo2-lacZ ES cells but none occurred from null Lmo2-lacZ ES cells. Therefore, in this model Lmo2 is an obligatory regulator of neo-vascularization of tumours. These data suggest that LMO2 function may be a drug target in cancer and other conditions characterized by neo-vascularization.

Angiostatin enhances B7.1-mediated cancer immunotherapy independently of effects on vascular endothelial growth factor expression.

Tumors must develop an adequate vascular network to meet their increasing demands for nutrition and oxygen. Angiostatin, a multiple kringle (1-4)-containing fragment of plasminogen, is an effective natural inhibitor of tumor angiogenesis. Here we show that gene transfer of angiostatin into small (0.1 cm in diameter) solid EL-4 lymphomas established in syngeneic C57BL/6 mice led to reduced tumor angiogenesis and weak inhibition of tumor growth. In contrast, when angiostatin gene therapy was preceded by in situ gene transfer of the T-cell costimulator B7.1, large (0.4 cm in diameter) tumors were rapidly and completely eradicated, whereas B7.1 and angiostatin monotherapies were ineffective. Combined gene transfer of B7.1 and angiostatin generated potent systemic antitumor immunity that was effective in eradicating a systemic challenge of 10(7) EL-4 cells. Gene transfer of angiostatin expression plasmids led to overexpression of angiostatin in tumors, increased apoptosis of tumor cells, and decreased density of tumor blood vessels, which may allow the immune system to overcome tumor immune resistance. The latter effects were not the result of a decrease in vascular endothelial growth factor expression, as tumoral vascular endothelial growth factor expression increased slightly after angiostatin gene transfer, presumably in response to increasing hypoxia. These results suggest that combining immunogene therapy with a vascular attack by angiostatin is a particularly effective approach for eliciting antitumor immunity.

Preoperative embolization followed by surgical excision of a giant thymic carcinoid.

We report the case of a 35-year old woman with a giant thymic carcinoid of the left hemithorax. Enhanced computed tomography showed marked vascularization of the tumour, with an enlarged drainage vein. Endovascular embolization of the major feeding arteries of the tumour was performed preoperatively with good angiographic results. A left thoracotomy was performed the following day. Minimal bleeding was observed due to prior embolization. The patient made a rapid postoperative recovery and was discharged 8 days later.

Ruptured thymoma managed via thoracotomy.

Thymomas rarely present with chest pain due to hemorrhage. This could cause shortness of breath if it ruptures into the pleural space, and is best managed surgically. We describe the case of an 83-year-old woman who presented with such symptoms. Computed tomography showed a ruptured mediastinal mass with pleural effusion. She was managed successfully by thoracotomy with excision of the mass and drainage of the effusion. Histopathology revealed a ruptured thymoma with infarction and necrosis.

Characterization of malignant thrombus in an invasive thymoma with intravascular growth.

We report an unusual case of an invasive thymoma with a thrombus in the right atrium and describe the radiological findings consistent with the malignant nature of the thrombus. The thrombus showed significant enhancement on computerized tomography images similar to the tumoral mass. On magnetic resonance imaging, both the tumor and the thrombus have heterogeneously high signal intensities on T2-weighted images. On diffusion-weighted images they both exhibit high signal intensity and low apparent diffusion coefficient (ADC) values which support the malignant nature of the thrombus and the mass.

[Correlation of CKP and VEGF expression and microvessel density to spiral CT manifestations of thymoma].

OBJECTIVE: To investigate the correlation of cytokeratin pan (CKP), vascular endothelial growth factor (VEGF) expression and microvessel density (MVD) to spiral CT manifestations of thymoma. METHODS: Eighty-four thymoma patients were underwent spiral CT examination, and 40 of the patients also had enhanced CT examination. All the CT findings were carefully reviewed to analyze their correlation to the expressions of CKP, VEGF and MVD. RESULTS: The enhancement on spiral CT images increased with the levels of VEGF expression and MVD counting (P<0.01). Significant correlations were observed between VEGF expression, MVD counting and such spiral CT findings as lobular contours, cusp-like or sawtooth-like margins and tumor invasions of the pleural membrane, pericardium and great vessels (P<0.05). CKP expression showed no obvious correlation to these findings by spiral CT. CONCLUSION: Spiral CT can reflect the pathological characteristics of thymoma, and may serve as a noninvasive modality for preoperative evaluation of thymoma.

Spontaneous regression of symptomatic thymoma caused by infarction.

We herein report a 38-year-old man who had spontaneous regression of a thymoma with repeating episodes of chest pain that initially occurred 2 years earlier when the tumor was 35 mm in the long axis. Left video-assisted thoracoscopic thymothymectomy was performed. Pathology examination showed a thymoma 15 mm in the long axis, classified B2 in the World Health Organization classification and stage II by Masaoka staging. The feeding arteriole of the tumor, occluded by organized thrombi, was suggested to be the cause of coagulation necrosis. The patient recovered well from surgery without complication and with no episodes of chest pain at the 9-month outpatient follow-up.

Acute presentation of thymoma with infarction or hemorrhage.

The presentation of thymomas is variable; most are asymptomatic and others present with local compression symptoms or a parathymic syndrome. Rarely thymomas present as an acute emergency with severe chest pain from either infarction or hemorrhage of the tumor. This rare presentation usually leads the clinician initially away from the diagnosis of thymoma. We present 4 patients who presented with infarction (3 patients) and hemorrhage (1 patient) who were initially believed to have a lymphoma. Preoperative biopsies were unrevealing. All had a complete resection and were in the early Masaoka stage. There have been no recurrences in follow-up. The astute clinician should be aware of this unusual presentation. The prognosis seems to be good in patients who present with infarction or hemorrhage.

[Intravascular invasion of a thymoma from the thymic vein to the right atrium--a case report].

A 43-year-old woman with a complaint of facial swelling was admitted to our hospital. A chest roentgenogram revealed a mass in the mediastinum. Chest CT and MRI demonstrated a mass in the anterior mediastinum protruding into the superior vena cava (SVC) and right atrium. A diagnosis of thymoma was made by needle biopsy. The patient underwent surgery without preoperative treatment. The tumor extended across the capsule of hte thymic gland and a polypoid growth of tumor reached the right atrium through the lumen of the thymic and left brachiocephalic veins and the SVC. No direct infiltration into the SVC or pericardial cavity was observed. Under cardiopulmonary bypass, the tumor was resected with the left brachiocephalic vein, SVC, and the upper third of the right atrium. The SVC was reconstructed using an EPTFE graft. Histopathologic examination demonstrated a predominantly epithelial cell thymoma. Adjuvant chemotherapy was performed, and no recurrence has been recognized for 3 years postoperatively.