[Epithelial tumors with thymus differentiation of the thyroid gland and the neck]

Epithelial tumors with thymus-like differentiation occurring in the thyroid gland and the neck, delineate four entities with distinct histological features and different behaviour. The spindle epithelial tumors with thymus-like differentiation are potentially malignant tumors occurring in the thyroid gland of young patients. They are highly cellular with pattern of spindle cells and tubulopapillary formations and mucinous glands. Carcinomas showing thymus-like differentiation of the thyroid gland are histologically identical to some thymic carcinomas. The ectopic hamartomatous thymoma is strictly benign and occurs in the soft tissues of the lower neck. It is characterized by spindle and solid or cystic islands of epithelial cells associated with adipose cells. The ectopic cervical thymoma is usually benign and histologically similar to mediastinal thymomas. All these tumors are particularly rare and arise from ectopic thymus or remnants of branchial pouch. The differential diagnoses of these tumors can be difficult and include some other proliferations occurring in the neck.

[Thymolipoma--a rare histological finding in patients with myasthenia gravis]

Over a 15-year period, thirteen thymolipomas are histologically demonstrated in a total of 182 myasthenia gravis patients undergoing thymectomy. The incidence of this rare histological diagnosis in the aforementioned group appears to be considerably higher than the one so far reported in the pertinent literature. In the series reviewed men in advanced age prevail which is by no means typical of myasthenia patients. The postoperative results are very good, with not a single fatal outcome being recorded. There are basically three types of histological findings in thymolipomas--fat tissue alone, fat tissue with thymic tissue in involution, and fat tissue with thymic tissue.

Solitary fibrous tumor arising from hyperplastic thymus

One case of a solitary fibrous tumor arising from the hyperplastic thymus is recorded. The patient was a 37-year-old female who presented with an anterior mediastinal mass. Thoracotomy was performed and revealed that the tumor arose on a pedicle from the posteroinferior surface of the enlarged thymus. The pathologic findings were characteristic of a solitary fibrous tumor. This is a very rare neoplasm that occurred in the mediastinum and had evidence of thymus gland in origin.

B-cell lymphoma of mucosa-associated lymphoid tissue of the thymus: a report of two cases with a background of Sjögren's syndrome and monoclonal gammopathy

Two rare cases of low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) arising in the thymus are reported. Both patients (a 61-year-old man and a 75-year-old woman) were suffering from Sjögren's syndrome and immunoglobulin (Ig)A kappa monoclonal gammopathy. Mixed IgA-IgG cryoglobulinemia was also present in the male case. Tumor cells expressed IgA and kappa antibody reactive proteins identical with serum IgA kappa M. Moreover, we could demonstrate rearrangements of the immunoglobulin heavy and light chain genes, which supported the monoclonal origin of tumor cells. Immunological abnormalities improved after thymectomy in one case in which the tumor cells were confined to the thymus, but not the other with regional lymph node involvement, suggesting a causal role for the tumor. MALT lymphomas of the thymus thus appear to be associated with immunological disorders such as Sjögren's syndrome or monoclonal gammopathy.

Immaturity of lymphocytes in the metastatic lesions of thymoma

Thymoma is a thymic epithelial tumor which often contains a large number of immature T cells. Although the metastatic lesions are also associated with abundant lymphocytes, their characteristics have not been assessed in detail. In this study, the phenotype was analyzed and compared with those in their primary lesions. Nine metastatic thymomas were obtained from seven patients. In the metastatic lesions, CD1a+ cells and CD4(+)CD8(+) cells accounted for 77.7 +/- 10.6 and 52.3 +/- 15.8% of all the lymphocytes, respectively. In five primary lesions and their metastatic lesions, CD3(-)CD4(+)CD8(-) cells accounted for 23.9 +/- 16.9 and 45.2 +/- 15. 5% of the CD4(+)CD8(-) cells, respectively. CD69 was expressed on 70. 9 +/- 9.5 and 53.1 +/- 11.8% of the CD4(+)CD8(-) cells, respectively. These results indicate that the metastatic lesions of thymoma are associated with abundant immature T cells which are phenotypically less mature than those in their primary lesions.

[Association of thymoma and severe intestinal strongyloidiasis]

A 59-years-old man with thymoma and severe intestinal strongyloidiasis is reported. The authors pointed out a possible influence of immunological response related with thymoma in the development of hyperinfection by Strongyloides stercoralis.

Protection from lymphoma cell metastasis in ICAM-1 mutant mice: a posthoming event

It has been hypothesized that the intercellular adhesion receptors used by normal cells could also be operative in the spreading of circulating malignant cells to target organs. In the present work, we show that genetic ablation of the ICAM-1 gene confers resistance to T cell lymphoma metastasis. Following i.v. inoculation of LFA-1-expressing malignant T lymphoma cells, we found that ICAM-1-deficient mice were almost completely resistant to the development of lymphoid malignancy compared with wild-type control mice that developed lymphoid tumors in the kidneys, spleen, and liver. Histologic examinations confirmed that ICAM-1-deficient mice, in contrast to wild-type mice, had no evidence of lymphoid infiltration in these organs. The effect of ICAM-1 on T cell lymphoma metastasis was observed in two distinct strains of ICAM-1-deficient animals. Nonetheless, lymphoma cells migrated with the same efficiency to target organs in both normal and ICAM-1-deficient mice, indicating not only that ICAM-1 expression by the host is essential in lymphoma metastasis, but also that this is so at stages subsequent to homing and extravasation into target organs. These results point to posthoming events as a focus of future investigation on the control of metastasis mediated by ICAM-1.

Identification of haemopoietic biglycan in hyperplastic thymus associated with myasthenia gravis

Generally biglycan, a small proteoglycan, has been thought to play a role as an extracellular matrix and/or a reservoir for other factors, such as TGF-beta and collagens. Recently, we have found that a soluble 100 kDa biglycan, produced from the rat thymic myoid cells and the brain glial cells, predominantly stimulates growth and differentiation of monocytic lineage cells from various lymphatic organs, including microglias. In the present study, we attempted to identify biological significance of the corresponding molecules in human, using five myasthenic thymuses (three with hyperplasia and two with thymoma) that had been surgically removed for therapeutic purpose. With immunohistochemistry, many biglycan positive cells were detected in the germinal center of the three hyperplastic thymuses, but not in the two thymuses associated with lymphocytic thymoma. Biglycan purified from the hyperplastic thymuses by an immunoaffinity column was found as a monomer with apparent molecular size of 95-100 kDa and self associated oligomers of greater than 201 kDa. The purified biglycan markedly stimulated the growth and differentiation of monocytic cells from haemopoietic stem cells of the rat bone marrow. These results suggest that particular cells, which produce haemopoietic biglycan, play significant roles in generation and maintenance of the hyperplastic changes associated with myasthenia gravis.

Radio-sensitive murine thymoma cell line 3SB: characterization of its apoptosis-resistant variants induced by repeated X-irradiation

3SB, a mouse thymoma cell line, is one of the most radio-sensitive cells (D0 = 0.3 Gy), and its rapid apoptosis (4 h after 5 Gy irradiation, 90% apoptosis) seems to play a decisive role in enhancing the radiosensitivity. To understand the molecular mechanisms underlying extremely high radiosensitivity and rapid apoptosis, we attempted to isolate X-ray-resistant (XR) variants from 3SBH5, a stable subclone of 3SB, by repeating exposure of the cells to 2-5 Gy X-rays. Four independent stable XR variants, R111, R223, R316 and R429, were isolated by the repeated irradiation protocols. All XR cells possessed about 3 times higher D10 values than that of their parental 3SBH5. They were also resistant to apoptosis; only 10% cells underwent apoptosis 4 h after 5 Gy irradiation. The p53 protein was induced in all the cell lines after 5 Gy X-irradiation. These variants showed a cross resistance to a chemical reagent daunorubicin (DNR) that is known to be involved in the ceramide-mediated apoptosis. DNR, as well as C2-ceramide (5 muM) induced apoptosis in parental 3SBH5 cell, but not in two XR variants, R233 and R316 cells. Present result suggests that the induction of X-ray resistance by repeated X-irradiation might be achieved, at least partly, by the enhanced resistance to the ceramide-mediated apoptosis.

Thymic neoplasia as represented by fine needle aspiration biopsy of anterior mediastinal masses. A practical approach to the differential diagnosis

OBJECTIVE

To evaluate the cytomorphology of thymoma and to discuss the potential diagnostic pitfalls and a practical approach, which sometimes uses ancillary studies, in distinguishing various lesions of anterior mediastinal masses.

STUDY DESIGN

A review of 25 fine needle aspiration (FNA) specimens of anterior mediastinal masses of thymic origin from 24 patients.

RESULTS

The FNA diagnoses were thymoma in 16 aspirates, thymic/poorly differentiated carcinoma in 2, necrotic fluid/debris in 2, small lymphocytic proliferation in 2, hyperplastic thymic tissue in 1, benign cyst in 1, and scant tissue in 1. In 22 cases that had histologic confirmation, the diagnoses of 19 (86%), including 14 thymomas, concurred with the FNA diagnoses. Sampling error was responsible for the discrepancy in the remaining three cases. The cytologic evaluation of thymoma revealed a characteristic dual population of predominantly small lymphocytes and occasional large, atypical lymphocytes intimately admixed with relatively bland epithelial cells. Differential diagnoses of thymoma in the mediastinal aspirates included a variety of entities, depending on which component predominated.

CONCLUSION

FNA of anterior mediastinal thymic lesions generally yields adequate cellular tissue with distinct cytologic and immunophenotypic features that enable precise classification. Caution in interpretation should be taken when the FNA yields only necrotic fluid or scanty material or when the patient is younger than the typical age range for thymoma. When the FNA diagnosis is coupled with clinical and radiographic findings, a definitive diagnosis can be generally rendered without open biopsy.

Ku70: a candidate tumor suppressor gene for murine T cell lymphoma

We present evidence that inactivation of the Ku70 gene leads to a propensity for malignant transformation both in vitro and in vivo. In vitro, Ku70-/- mouse fibroblasts displayed an increased rate of sister chromatid exchange and a high frequency of spontaneous neoplastic transformation. In vivo, Ku70-/- mice, known to be defective in B but not T lymphocyte maturation, developed thymic and disseminated T cell lymphomas at a mean age of 6 months with CD4+CD8+ tumor cells. These findings directly demonstrate that Ku70 deficiency facilitates neoplastic growth and suggest a novel role of the Ku70 locus in tumor suppression.

Natural history and treatment of malignant thymoma

Thymomas are rare, slow-growing neoplasms that are considered to be malignant because of their potential invasiveness. The most widely used staging system is that of Masaoka and colleagues, which takes into account the extent of clinical and histopathologically determined disease involvement. However, recent data suggest that the staging system of the French Study Group on Thymic Tumors (GETT system), which is based on the surgical and pathologic features of the tumor, may be superior to the Masaoka system. Total resection followed by radiation therapy is the treatment of choice for all thymomas, except stage IA tumors, which can be treated with surgery alone. Chemotherapy can improve the outcome of invasive Masaoka stage III and IV thymomas or recurrent thymomas. Only platinum-containing regimens show consistent efficacy.

Metabolic (PET) and receptor (SPET) imaging of well- and less well-differentiated tumours: comparison with the expression of the Ki-67 antigen

[111In-DTPA-D-Phe1]-pentetreotide has been shown to localize well-differentiated and slowly growing neuroendocrine tumours, whereas increased FDG uptake is associated with malignancy. This prospective study explores the role of metabolic (PET) and receptor (SPET) imaging in well- and less well-differentiated tumours--gastroenteropancreatic (GEP) tumours, medullary thyroid carcinomas (MTC) and thymic carcinomas--in comparison with the expression of the Ki-67 antigen. Ten patients with GEP tumours, five with MTC and five with thymic carcinomas were studied. Prior to PET, somatostatin receptor scintigraphy (SRS) was performed in all patients. Sixty minutes after the intravenous administration of 18F-FDG (370 MBq), whole-body PET was performed. In addition, the resected tissues were prepared for immunocytochemistry examination (cell cycle-associated Ki-67 antigen). Preoperative SRS detected multiple primary tumours and metastatic lesions in four patients with well-differentiated carcinoids (low Ki-67 expression). Whole-body PET demonstrated normal distribution of FDG in all of these patients. In patients with recurrent MTC and rapidly increasing CEA levels, SRS showed no in vivo somatostatin receptor expression, whereas whole-body PET localized 24 locoregional lymph node metastases with increased FDG uptake. Immunocytochemistry of the resected lymph nodes demonstrated high Ki-67 expression associated with a high proliferative activity. Similar results in receptor scintigraphic and metabolic behaviour were obtained from patients with metastasizing thymic carcinomas (high Ki-67 expression). In conclusion, SRS has been shown to localize well-differentiated GEP tumours. In contrast, FDG PET is only valuable for predicting malignancy in less well-differentiated GEP tumours and malignant MTC associated with rapidly increasing CEA levels. Therefore, an additional 18F-FDG PET procedure should only be performed if SRS is negative. Furthermore, our preliminary results suggest that increased FDG metabolism reflects the invasiveness of thymic carcinomas.

Surgery for invasive primary mediastinal tumors

BACKGROUND

There have been few reports on results after extended radical resection for primary mediastinal tumors invading neighboring organs.

METHODS

A retrospective analysis of 89 patients who underwent total or subtotal resection of a primary mediastinal tumor with resection of at least part of an adjacent structure between 1979 and 1995 was performed. Clinical data were collected from the medical records.

RESULTS

There were 35 invasive thymomas, 12 thymic carcinomas, 17 germ cell tumors, 16 lymphomas, 3 neurogenic tumors, 3 thyroid carcinomas, 2 radiation-induced sarcomas, and 1 mediastinal mesothelioma. The tumor was located in the anterior mediastinum in 74% of patients. Residual masses after chemotherapy were excised in 14 patients with germ cell tumor and 8 with lymphoma. A median sternotomy was the most frequently used approach (79% of patients). Total resection was achieved in 79% and significantly improved survival (p < 0.01). Adjacent resected structures included 38 phrenic nerves, 21 superior venae cavae, 16 upper lobes, and 13 innominate veins, in 5 patients, a pneumonectomy was required. The complication rate was 17% and the mortality rate, 6%. With follow-up available for 86 patients, the overall 5-year survival rate was 69% for patients with thymoma, 42% for patients with thymic carcinoma, 48% for patients with germ cell tumor, and 83% for patients with lymphoma.

CONCLUSIONS

Malignant mediastinal tumors can be safely resected even if they have invaded other mediastinal structures. Complete resection is important to achieve satisfactory long-term survival. A median sternotomy is an excellent approach, and a preoperative diagnosis by biopsy is desirable. Residual masses after chemotherapy for lymphoma or germ cell tumor should be resected. Extensive resection without a preoperative diagnosis is not indicated.

Reconstruction of the aortic arch in invasive thymoma under retrograde cerebral perfusion

Extensive en-bloc resection of the aortic arch and anterior wall of the main pulmonary artery was performed in a 46-year-old man with invasive thymoma. The aortic arch was replaced with a Hemashield vascular graft under hypothermic circulatory arrest with retrograde cerebral perfusion. Patch plasty with Xenomedica was performed for the anterior wall of the main pulmonary artery under cardiopulmonary bypass. The patient was treated with postoperative radiotherapy and has remained asymptomatic for 15 months after the operation. An extensive operation is considered necessary to improve the prognosis of invasive thymoma.

Papillary carcinoma of the thymus: report of four cases of a new microscopic type of thymic carcinoma

We describe four cases of papillary carcinoma arising in the thymus. Three showed low-grade atypia and were associated with spindle cell-type thymoma. The fourth case showed high-grade atypia and had no evidence of an association with thymoma. Two of three low-grade cases invaded the lung and showed extensive lymphatic permeation. Cyst formation was seen in one case. Immunohistochemically, the tumor cells were positive for carcinoembryonic antigen (CEA), Leu-M1, Ber-EP4, calretinin (2 cases), and CD5 and were negative for thyroglobulin and pulmonary surfactant apoprotein. Ultrastructural findings for the one case studied by electron microscopy gave evidence against a mesothelial origin of the tumor. The histologic similarities and the intimate association with spindle cell thymoma indicate that papillary thymic carcinoma may arise from the papillotubular formations sometimes seen in the former tumor. Papillary thymic carcinoma, a lesion hitherto undescribed, should be considered in the differential diagnosis of anterior mediastinal tumors. Conceivably, it may be the source of some metastatic papillary carcinomas with or without psammoma bodies in cervical lymph nodes, in which no tumor is found in the thyroid gland.

[Atypical carcinoid tumor of the thymus]

We report a male patient with atypical carcinoid tumor diagnosed by anterior mediastinotomy and biopsy after a mass was observed by chance on a chest film. The presence of neuroendocrine markers, notably chromogranin, cytokeratin, synapto-physin and neuro-specific enolase, facilitated diagnosis. Because the tumor was infiltrative, full surgical excision and radiotherapy to the mediastinum (50 Gy) were provided. We describe the incidence, clinical presentation, diagnosis, treatment and prognosis of these tumors.

Thymic carcinoids in multiple endocrine neoplasia type 1

OBJECTIVE

To study the clinical, pathologic, and genetic features of thymic carcinoids in the setting of multiple endocrine neoplasia type 1 (MEN1) and to study means for detection and prevention of this tumor in patients with MEN1.

SUMMARY BACKGROUND DATA

Thymic carcinoid is a rare malignancy, with approximately 150 cases reported to date. It may be associated with MEN1 and carries a poor prognosis, with no effective treatment. Its underlying etiology is unknown.

METHODS

Ten patients with MEN1 from eight families with anterior mediastinal tumors were included in a case series study at tertiary referring hospitals. Clinicopathologic studies were done on these patients, with a review of the literature. Mutation analysis was performed on the MEN1 gene in families with clusterings of the tumor to look for genotype-phenotype correlation. Loss of heterozygosity was studied in seven cases to look for genetic abnormalities.

RESULTS

Histologic studies of all tumors were consistent with the diagnosis of thymic carcinoid. Clustering of this tumor was found in some of the families-three pairs of brothers and three families with first- or second-degree relatives who had thymic carcinoid. All patients described here were men, with a mean age at detection of 44 years (range 31 to 66). Most of the patients had chest pain or were asymptomatic; none had Cushing's or carcinoid syndrome. All tumors were detected by computed tomography (CT) or magnetic resonance imaging (MRI) of the chest. The results of octreoscans performed in three patients were all positive. Histopathologic studies were consistent with the diagnosis of thymic carcinoid and did not stain for ACTH. Mutation analysis of the families with clustering revealed mutations in different exons/introns of the MEN1 gene. Loss of heterozygosity (LOH) studies of seven tumors did not show LOH in the MEN1 region, but two tumors showed LOH in the 1p region.

CONCLUSIONS

MEN1-related thymic carcinoids constitute approximately 25% of all cases of thymic carcinoids. In patients with MEN1, this is an insidious tumor not associated with Cushing's or carcinoid syndrome. Local invasion, recurrence, and distant metastasis are common, with no known effective treatment. We propose that CT or MRI of the chest, as well as octreoscanning, should be considered as part of clinical screening in patients with MEN1. We also propose performing prophylactic thymectomy during subtotal or total parathyroidectomy on patients with MEN1 to reduce the risks of thymic carcinoid and recurrence of hyperparathyroidism. Its male predominance, the absence of LOH in the MEN1 region, clustering in close relatives, and the presence of different MEN1 mutations in these families suggest the involvement of modifying genes in addition to the MEN1 gene. A putative tumor suppressor gene in 1p may be involved.

Thymoma. Cytopathologic features and differential diagnosis on fine needle aspiration

OBJECTIVE

Cytopathologic descriptions of thymoma are limited. This study was undertaken to elaborate on the cytomorphologic features along with clinicoradiologic findings of this entity, with special emphasis on the differential diagnosis.

STUDY DESIGN

Twenty cases of thymoma were retrospectively studied. Material was obtained by fine needle aspiration (FNA). Smears were stained with Diff-Quik and Papanicolaou stain, and cell block sections were stained with hematoxylin and eosin. Immunocytochemical (ICC) studies were done in selected cases using cytokeratins, epithelial membrane antigen, carcinoembryonic antigen, placental alkaline phosphatase, neuron-specific enolase, chromogranin and lymphocytic markers (CD3 and UCHL-1).

RESULTS

Fourteen thymomas were from the anterior mediastinum; the remaining 6 were invasive or metastatic to the lung (2), pleura (2), liver (1) and abdominal wall (1). The key diagnostic feature was a biphasic population of epithelial cells and lymphocytes in varying proportions. Medullary thymomas showed cohesive, spindled epithelial cells, whereas cortical subtypes displayed more epithelioid epithelial cells singly and in discohesive clusters. All cases of invasive or metastatic thymoma were of the cortical subtype. ICC studies were positive for cytokeratins and epithelial membrane antigen.

CONCLUSION

FNA, coupled with clinicoradiologic information and appropriate immunocytochemical studies, is highly accurate in the diagnosis of primary and metastatic thymomas.

Spindle epithelial tumour with thymus-like element (SETTLE): the predominantly monophasic variant

AIMS

To describe two cases of spindle epithelial tumour with thymus-like element (SETTLE) which are composed predominantly of spindle cells. In addition, to highlight some unusual histological features in SETTLE and discuss its separation from histological mimics.

METHODS AND RESULTS

The thyroid masses were in a 4-year-old boy and a 25-year-old male. Both patients were euthyroid and were well except for thyromegaly. The specimens were formalin fixed, and immunohistochemistry was performed on this material using a panel of antibodies following microwave antigen retrieval. Morphologically, the dominant pattern was of sheets of spindle cells arranged in several patterns. There was mild pleomorphism and occasional mitoses. There were very small foci of squamous epithelium and occasional ductular structures. The stroma was composed of fibrous tissue and isolated areas of calcification were noted. The spindle cells showed strong and diffuse immunoreactivity with AE1/3, CAM5.2 and vimentin.

CONCLUSION

We describe two cases of SETTLE that are composed mainly of spindle cells and only a very focal ductular component. In addition, calcification was noted within the stroma in one of the cases. These predominantly spindle examples of SETTLE must be separated from synovial sarcoma, which is a more mitotically active, aggressive tumour displaying only patchy immunopositivity with epithelial markers.

Thymic lymphoepithelioma-like carcinoma associated with thymoma in a patient with ocular myasthenia

A 65-year-old woman with ocular myasthenia was found to have three tumours in the anterior mediastinum, revealed by magnetic resonance imaging. All three lesions were radically resected. Histologically, one was a mixed-type thymoma, one a thymic lymphoepithelioma-like carcinoma, and the third had features of both these types. This appears to be the first reported case of coexisting thymic lymphoepithelioma-like carcinoma (TLC) and thymoma associated with ocular myasthenia.

p53 deficiency and misexpression of protein kinase CK2alpha collaborate in the development of thymic lymphomas in mice

Protein kinase CK2 (casein kinase II) is a serine-threonine protein kinase with many substrates, some of which are involved in cell cycle regulation. CK2 activity is elevated in human solid tumors and leukemia, and dysregulated expression of CK2 induces lymphoma in transgenic mice. Mice that are deficient in p53 also develop lymphomas, and p53 activity may be regulated by CK2 phosphorylation. Here we demonstrate that CK2alpha transgenic mice partially or completely deficient in p53 develop thymic lymphomas at a markedly accelerated rate when compared to p53-deficient mice lacking the transgene. Lymphomas originating from CK2alpha transgenic mice that are heterozygous for p53 generally lose the wild type p53 allele, indicating that loss of p53 is an important step in tumor progression. Moreover, though lymphomas occur as early as 3 weeks of age in the transgenic mice that are nullizygous for p53, they are still monoclonal, indicating that additional stochastic mutations are required for their development. These lymphomas express high levels of myc mRNA and frequently ectopically express Lmo-2, a transcription factor involved in human T cell acute lymphocytic leukemia. The p53-null CK2alpha transgenic lymphomas grow rapidly but are highly prone to apoptosis, suggesting that transformation occurs through synergistic dysregulation of cell cycle control induced by misexpression of CK2 and loss of function of p53.