[Clinicopathologic study of metaplastic thymoma].

OBJECTIVE: To study the clinicopathologic characteristics of metaplastic thymoma. METHODS: Resection specimens of 3 cases of metaplastic thymoma were studied by light microscopy, immunohistochemistry and electron microscopy. RESULTS: All the 3 patients were females and aged 33, 58 and 45 years respectively. Histologically, a biphasic growth pattern, consisting of intimate admixture of epithelial cells and spindle cells, was noted. The epithelial cells showed mild cytologic atypia, sometimes nuclear grooves and pseudonuclear cytoplasmic inclusions. These cells were arranged in nests and anastomosing cords. Mitotic figures were rarely seen. On the other hand, the spindle cells were bland-looking, mitotically inactive and arranged in fascicles. Immunohistochemical study showed that the epithelial cells strongly expressed cytokeratin (AE1/AE3) but not vimentin or CD5. The proliferation index, as demonstrated by Ki-67 immunostaining, was about 3% to 5%. In contrast, the spindle cells were diffusely positive for vimentin and epithelial membrane antigen. Staining for CD5 and CD20 was negative. The background lymphocytes were positive for CD3, but not for TdT and CD99. Ultrastructurally, well-formed desmosomes or hemidesmosomes were identified in the epithelial element. They were not detected within the spindle cells. CONCLUSION: Metaplastic thymoma is a rarely encountered indolent or low-grade thymic tumor and may represent a distinct clinicopathologic entity.

Primary intrapulmonary spindle cell thymoma with marked granulomatous reaction: report of a case with review of literature.

Primary intrapulmonary thymoma is a rare lesion with around 20 cases reported so far in the literature. A pure spindle cell morphology in these lesions is rarer still with only a single case recorded to date. We report herein an interesting case of a 47-year-old-man, status post surgical resection and radiotherapy for a squamous cell carcinoma of the floor of mouth, who was being followed up for a radiologic opacity in the right lower lobe of the lung. The lesion remained stable in size for almost 5 years and then an increase in size was noted. A right lower lobectomy was performed with a preoperative suspicion of metastasis. Histologic and immunohistochemical evaluation revealed a primary intrapulmonary spindle cell thymoma that displayed a prominent granulomatous reaction, a phenomenon not described so far in the literature. We discuss the possible embryologic origins and the pitfalls in diagnosis of these rare neoplasms. The remarkable granulomatous response observed in the tumor raises the possibility that similar lesions might conceivably occur in the thymus as well.

Ectopic hamartomatous thymoma: a case report showing CD99+ lymphocytes and a low proliferation index.

Ectopic hamartomatous thymoma is a rare benign tumor that consists of spindle, epithelial, and adipose cell elements. We present a case of this lesion arising in the supraclavicular region of a 59-year-old man, including the characteristic immunohistochemical and ultrastructural findings. DNA flow cytometry revealed diploidy with a low proliferation index (6.73%). The tumor contained CD99+ lymphocytes; CD99 (MIC2) can serve as a useful marker of immature T cells. These findings suggest that ectopic hamartomatous thymoma may develop from the third branchial pouch or thymic anlage.

Sex steroid hormone receptors in human thymoma.

In this study we examined the immunohistochemical localization of sex steroid receptors for estrogen alpha (ER alpha) and ER beta, progesterone-A (PR-A) and PR-B, and androgen (AR) in human thymoma (n = 132) and correlated these findings with various clinicopathological parameters. We used RT-PCR and real-time PCR to further study the expression of these receptors in 20 thymoma cases. Immunoreactivity for all sex steroid receptors was detected in the nuclei of thymoma epithelial cells. The percentage of immunopositive cases and the H-score values for each receptor (mean +/- SD) were: ER alpha, 66% and 85.8 +/- 80.2; ER beta, 7% and 7.2 +/- 8.7; PR-A, 4% and 2.7 +/- 4.9; PR-B, 49% and 55.8 +/- 68.3; and AR, 15% and 14.1 +/- 11.7, respectively. The results of real-time PCR were consistent with those of immunohistochemistry, especially results for ER alpha, PR-B, and AR. A significant positive correlation was detected between immunoreactivity for ER alpha and PR-B. ER alpha immunoreactivity was inversely correlated with tumor size, clinical stage, WHO classification, and Ki-67 labeling index. In addition, the status of ER alpha immunoreactivity was significantly associated with a better clinical outcome in thymoma patients. Results from our study suggest that estrogens may inhibit thymoma growth via ER alpha, and that ER alpha immunoreactivity may act as a prognostic factor in human thymoma.

Ectopic hamartomatous thymoma: a case report with immunohistochemical and ultrastructural studies.

A case of ectopic hamartomatous thymoma (EHT) arising in the supraclavicular region of a 52-year-old male is presented. The well-defined tumor measuring 1.7x1.5x0.7 cm consisted of three components: spindle cell (70%), epithelial (25%), and adipose (5%). The spindle cell component was characterized by sheet-like, haphazard and short fascicular arrangements of bland spindle cells. Neither mitotic figures nor cellular pleomorphism were found. Admixed with, and adjacent to, the spindle cell areas was an obviously epithelial component of variable appearance, ranging from glandular spaces lined by mainly cuboidal clear cells, irregularly anastomosing cords, and strands of epithelial cells to irregular solid nests of squamous epithelium with dark and clear cytoplasm. Myoepithelial cells were also observed. Immunohistochemically, the spindle cells were strongly and diffusely positive for cytokeratins and some of them were positive for BRST2, alpha-smooth muscle actin, and CD10. The tumor was negative for S-100 protein, glial fibrillary acidic protein, and CD34. Ultrastructurally, tonofilaments and desmosomes were observed in the spindle cells. The findings indicate an epithelial origin. The patient was well without recurrence or metastasis 8 months after excision. Pathologists and clinicians should be aware of the existence of ectopic hamartomatous thymoma in the supraclavicular or suprasternal region and should differentiate it from a high-grade sarcoma, such as biphasic synovial sarcoma or glandular malignant peripheral nerve sheath tumor.

Pseudodicentric (16;12)(q11;p11.2) in a type AB (mixed) thymoma.

Genetic alterations of thymomas are rarely described in the literature. In this study, a previously unreported instance of aberrant karyotypic change consisting of 45,XX,pseu dic(16;12) (q11;p11.2) [cp23]/87-90,idemx2[cp4] in a Masaoka Stage II mixed thymoma or type AB thymoma affecting a 56-year-old Chinese woman is detailed. Abnormalities involving 12p containing important tumor suppressor-like genes have been documented especially in hematological malignancies. Recently, recurrent losses involving 16q, a locus known to harbor several tumor suppressor genes, have been described in type C thymomas (squamous cell carcinoma), suggesting a possible relationship between type AB thymoma and type C thymoma. Whether these genes are involved in the pathogenesis of type AB thymoma remain to be clarified and it is currently unclear if cytogenetic studies may eventually play a role in the classification of thymic tumors.

Age changes of neuromuscular junctions in the extensor digitorum longus muscle of spontaneous thymoma BUF/Mna rats. A scanning and transmission electron microscopic study.

BUF/Mna rats spontaneously develop thymomas and cause muscle weakness of hind legs at an advanced age. This rat strain has been recognized as a suitable animal model for human myasthenia gravis or related myopathies. To characterize the structural changes of neuromuscular junctions (NMJs) in BUF/Mna rats, subneural apparatuses (SNAs) of extensor digitorum longus muscles of young-adult (4-month-old) and aged (22- to 25-month-old) male rats were examined using scanning and transmission electron microscopy. The SNAs of NMJs in young rats consist of complex labyrinthine gutters with numerous slit-like junctional folds. SNAs in aged BUF/Mna rats, however, are characterized by: (1) a group of cup-like depressions with very wide slit-like junctional folds in relatively large muscle fibers (the major type), (2) the presence of slit-like folds on the flat sarcoplasm outside the cup-like depressions or on the protruded sarcoplasm, and (3) winding gutters or a small number of round depressions with poorly developed synaptic folds in small and medium-sized muscle fibers (the minor type). Since similar structural changes have been reported in dystrophic mice or normally aged rats, it is suggested that both the slowly progressing muscle atrophy and age-dependent turnover of muscle fibers may occur in the aged BUF/Mna rats.

Neuroendocrine differentiation in thymic epithelial tumors with special reference to thymic carcinoma and atypical thymoma.

To determine the neuroendocrine (NE) features of thymic epithelial tumor, immunohistochemistry and electron microscopy studies were performed on eight NE tumors (thymic carcinoids) and 26 non-NE tumors (nine thymic carcinomas, five atypical thymomas, and 12 thymomas other than lymphocytic thymoma). Immunohistochemical studies were performed with antibodies against general markers for NE cells (synaptophysin, alpha subunit of a guanine nucleotide-binding protein, Go, and small-cell lung carcinoma cluster 1 antigen), and a broad panel of antibodies for hormonal substances. Thymic carcinoid showed synchronous diffuse immunoreactivity for the three NE markers and contained cells that were positive for a variety of hormonal products: human chorionic gonadotropin (hCG) alpha-subunit (eight of eight), hCG beta-subunit (three of eight), adrenocorticotropic hormone (ACTH) (three of eight), calcitonin (two of eight), calcitonin gene-related peptide (two of eight), and serotonin (one of eight). Conversely, although positivity for NE markers was neither synchronous nor diffuse in non-NE tumors, seven of nine thymic carcinomas, three of five atypical thymomas (focal or dispersed distribution), and none of the five thymomas were positive for at least two of these NE markers. A small number of neoplastic cells were positive for hCGalpha-subunit or ACTH in three thymic carcinomas and one atypical thymoma. Ultrastructurally, dense core granules (DCG) were much more frequent in thymic carcinoid, but several DCG-like granules were identified in 12 of 13 non-NE tumors with or without immunoexpression of NE markers. The presence of focal or dispersed NE cells in thymic carcinoma and atypical thymoma may reflect multidirectional differentiation within the tumor, which, like cytological atypia, epithelial CD5 expression, and lack of immature T cell infiltration, may be another feature of this group at thymic tumors.

Thymoma with pseudosarcomatous stroma: report of an unusual histologic variant of thymic epithelial neoplasm that may simulate carcinosarcoma.

Six cases are described of an unusual type of primary thymic epithelial neoplasm characterized by a biphasic epithelial/spindle cell morphology that closely resembled a carcinosarcoma. The patients were two women and four men 28-70 years of age. The tumors presented clinically as asymptomatic anterior mediastinal masses found incidentally on routine chest radiographs. All patients were treated by complete surgical excision. Grossly, the tumors consisted of well-circumscribed, encapsulated masses that measured 6-14 cm in greatest diameter and showed a gray-white, homogeneous, rubbery cut surface. Histologically, the lesions were composed of anastomosing islands and cords of oval to polygonal epithelial cells displaying large nuclei with occasional prominent nucleoli and rare mitotic figures, separated by areas containing a highly cellular spindle cell proliferation without nuclear atypia. Thymic remnants could be identified in the periphery of the lesions in four cases. Immunohistochemical stains showed diffuse strong positivity for keratin and focally for epithelial membrane antigen (EMA) in the epithelial cell component, and strong positivity for vimentin and focally for actin in the spindle cell stromal component. Stains for keratin, EMA, desmin, S-100 protein, and CD34 were negative in the spindle stromal cells in all cases except one, in which EMA positivity was present; CD5 stains were negative in the epithelial cells in all cases examined. Electron microscopic examination in one case showed well-formed desmosomes and tonofilaments in the epithelial elements, as well as features indicative of fibroblastic differentiation in the spindle stromal cells. Because of the unusually florid spindle cell stromal component and the focally atypical features of the epithelial cells, some of these tumors initially were misinterpreted as examples of carcinosarcoma. Clinical follow-up in five cases showed that the patients were alive and without evidence of disease over a period of 5-20 years (mean follow-up 10 years), suggesting a benign or very low grade malignant biologic behavior. The present cases appear to represent an unusual, previously undescribed morphologic variant of thymoma characterized by a prominent pseudosarcomatous stromal component. Because of the distinctive histologic appearance and indolent clinical behavior, these lesions should be distinguished from other more aggressive anterior mediastinal neoplasms displaying a biphasic morphology.

Immunohistochemical and in situ hybridization detection of growth-hormone-producing cells in human thymoma.

We have studied 25 thymomas by both immunohistochemistry and in situ hybridization for the presence of growth hormone (GH)-producing cells. Our results indicate that 1) GH-immunoreactive cells were present in 13 of 17 thymomas of cortical and predominantly cortical type but not in medullary (spindled) thymomas (n = 3) or low- to high-grade thymic carcinomas (n = 5), 2) GH-positive cells were mainly located at the periphery of the neoplastic lobules, at the periphery of the perivascular spaces and in the areas of medullary differentiation, 3) cells containing GH mRNA appeared at locations similar to those of GH-immunoreactive cells, and 4) GH-immunoreactive material was present only in the epithelial cell component as revealed by immunoelectron microscopy. In conclusion, this paper demonstrates the occurrence of GH-producing cells in noncarcinoid thymic tumors. The relevance of GH in thymoma cell biology requires additional investigations.

Spindle epithelial tumor with thymus-like differentiation: a case report with cytologic, histologic, immunohistologic, and ultrastructural findings.

Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a rare and distinctive low-grade neoplasm of thymic or related branchial pouch differentiation. The tumor usually presents in the thyroid or lateral neck of children and adolescents and could mimic spindle-cell carcinoma, synovial sarcoma, or malignant teratoma. We report the clinical, cytologic, histologic, immunohistochemical, and ultrastructural features of a SETTLE present for 10 years in a 15-year-old boy. The fine-needle aspirate, initially interpreted as synovial sarcoma, contained numerous clusters of bland spindle cells, with a few detached sheets of columnar mucous cells in a homogeneous background of dissociated spindle cells. Mitoses, necrosis, and atypia were not present. The excised tumor was a well-circumscribed, white-tan mass, with occasional microcysts. Microscopically, the mass consisted of a lobulated, highly cellular, spindle-cell neoplasm arranged in intersecting, whorled, and storiform fascicles separated by fibrous bands. Entrapped within the fibrous bands were squamous-lined cysts and benign-appearing glands lined by columnar epithelium with goblet cells or ciliated pseudostratified epithelium. Immunohistochemically, the spindle cells showed diffuse reactivity for cytokeratins, smooth muscle actin, muscle-specific actin, and MIC-2, and they were negative for epithelial membrane antigen, calcitonin, and thyroglobulin. Ultrastructurally, numerous perinuclear tonofilaments, some aligned with mature desmosomes, were identified in the spindle cells. Occasional cells showed thin filaments with fusiform dense bodies occupying the peripheral cytoplasm. These findings distinguish SETTLE from ectopic thymoma, synovial sarcoma, medullary carcinoma, and teratoma, and they support a thymic epithelial origin for SETTLE, possibly with myoepithelial differentiation.

Pitfalls in the diagnosis of ectopic hamartomatous thymoma.

We describe four cases of ectopic hamartomatous thymoma with unusual morphological features. In cases 1 and 2 we found a dysplastic glandular component which was often arranged in a cribriform pattern bridging several glandular spaces. In case 2 we found solid adenocarcinomatous areas with infiltrative edges. Case 3 showed widespread smooth muscle differentiation within the spindle epithelial cell component, the presence of multiple clear cell glands which contained a distinct myoepithelial layer and an overall picture which vaguely resembled a sclerosing adenosis of the breast. Case 4 contained frequent foci of multinucleated giant epithelial cells within the markedly cellular spindle cell component: it also showed multiple, hypocellular, myxoid areas containing eosinophilic cords and pearls of squamous cells, and resembled squamous cell carcinoma with a sarcomatoid spindle cell component. We could not find any evidence of a thymic origin or of thymic differentiation in our four cases or in any other reported cases of ectopic hamartomatous thymoma. We believe that ectopic hamartomatous thymomas manifest salivary gland differentiation.

Carcinoma arising in ectopic hamartomatous thymoma. An ultrastructural study.

We present the ultrastructural features of a case of adenocarcinoma arising in ectopic hamartomatous thymoma in a 31 year old man, in the supraclavicular location. The tumor had a cribriform adenomatous component with a granular cell quality and mimicked a metastatic carcinoma. Ultrastructurally, the spindle cell component revealed clusters of tonofilaments and the tumor cells were attached by well developed desmosomes. The cytoplasm of adenocarcinoma cells contained peculiar cup-shaped bodies derived from the endoplasmic reticulum wrapped around the mitochondria.

Thymic carcinoma of the thyroid.

A highly malignant case of intrathyroidal thymic carcinoma showing morphological and biochemical evidence identical with mediastinal thymoma is presented. A 32-year-old female, who had previously undergone total colectomy with ileo-proctostomy due to familial adenomatous polypnosis, was operated on for a tumor (3.4 x 4.5 cm) originating from the left thyroid lobe. A minute focus (diam. 0.8 cm) of papillary adenocarcinoma also existed in the upper pole of the right lobe. The main tumor was morphologically an epithelial thymoma with scanty lymphocyte intermixing and showed medullary differentiation with apparent Hassall's corpuscles. Mitosis was frequent and numerous tumor thrombi were in the subcapsular veins. Five months after the total thyroidectomy and lymph node dissection, a subcutaneous recurrence of the tumour (diam. 2.3 cm) appeared in the anterior cervical region. The cystic contents of the recurrent tumor revealed a high titer of thymosin alpha 1-Other organs, including thymus, lungs, and adrenals, had all been free of neoplastic changes clinically and radiologically for 5 months after her first admission until the local tumor recurrence.

[Study on ultrastructure morphology of fine needle aspiration of mediastinal and lung lesions].

Specimens of Mediastinal lesions and lung masses collected by fine needle aspiration (FNA) was examined with both light and transmission electron microscopy. Sixty eight specimens (9 mediastinal and 40 lung masses, 4 metastatic chest masses and 15 metastatic lymph nodes from lung cancer) from 104 cases (60.5%) were satisfactory for evaluation. With light microscopy, the nature of the lesions was assessed and the ultrastructural features of the lesions were evaluated with transmission electron microscopy. Diagnosis of histologic type of the lesions by light microscopy was consistent with that by transmission electron microscopy at a conformity rate of 50.4%. The results indicate that ultrastructural features are valuable in ascertaining histologic type of the lesions.

Giant desmosomes in tumors.

The lengths of desmosomal profiles were measured in sections of tumor tissue from cases of mesothelioma, adenocarcinoma, squamous cell carcinoma, thymoma, and meningioma. Giant desmosomes (length of profile 1 micron or greater than 1 micron) were found in all the above-mentioned tumors except adenocarcinomas. The largest desmosomal profile in adenocarcinoma was approximately 0.8 micron long; the largest in mesothelioma was approximately 2 microns long. Our observations suggest that one of the ways in which giant desmosomes arise is by growth and fusion of adjacent desmosomes. Giant desmosomes may at times help in distinguishing mesothelioma from adenocarcinoma, but this is a rather rare phenomenon. In this study giant desmosomes were found in only 2 out of 10 cases of mesothelioma.

Thymic epithelial neoplasms in transgenic mice expressing SV40 T antigen under the control of an erythroid-specific enhancer.

The beta-globin locus control region is known to be a powerful erythroid-specific enhancer. In an attempt to produce immortalized erythroid percursor cells, transgenic mice have been generated with the simian virus (SV) 40 T antigen gene under the control of the locus control region. As previously reported, transgenic mice did not develop erythroleukaemia, but rather succumbed to insulinomas and poorly differentiated rhabdomyosarcomas. This paper describes additional mice containing this transgene that developed thymomas of the mixed epithelial/lymphocytic type, in which only the epithelial component expressed the T antigen. Epithelial cell lines have been established from these tumours. This system may be useful in future studies on the pathogenesis of thymomas and the function of thymic epithelial cells.

Thymomas express epitopes shared by the ryanodine receptor.

Myasthenia gravis (MG) patients with thymoma have antibodies against ryanodine receptor (RyR) of skeletal and heart muscle. In this study, thymomas were examined for reactivity with a panel of polyclonal rabbit antibodies against various short peptides of RyR. An antibody against peptide C2 in the transmembrane region of RyR stained thymoma epithelial cells in cryosections of 17/23 thymomas, and detected a 40-kDa peptide in Western blotting of a thymoma membrane fraction. The other RyR antibodies did not react with thymoma tissue. The anti-C2 RyR antibody did not react with normal thymus, tonsil or carcinoma of colon. The results strongly indicate that epithelial thymoma cells express an epitope shared by the transmembrane region of skeletal and cardiac muscle RyR.

Kappa opioid receptors expressed on three related thymoma cell lines. Differences in receptor-effector coupling.

The mouse thymoma R1.1 cell line was shown previously to express a single high-affinity kappa 1 opioid receptor that is negatively coupled through a pertussis toxin-sensitive G-protein to adenylyl cyclase. This study compared opioid receptor binding and inhibition of adenylyl cyclase activity in three unique derivatives of the R1.1 cell line. Membranes from the R1.G1 and R1E/TL8x.1.G1.OUAr.1 (R1EGO) cell lines bound both [3H]U69,593 and [3H](-)-bremazocine with similar affinities compared with R1.1 membranes, whereas membranes from the R1E/TL8x.1 (R1E) cell line did not possess any opioid binding sites, detected by radioreceptor binding. The Bmax values for [3H]U69,593 and [3H]-(-)-bremazocine binding to R1.G1 and R1EGO cell membranes were, respectively, 3- and 6-fold greater than those obtained with the parent R1.1 cell line. GTP and its nonhydrolyzable analog, Gpp(NH)p, inhibited [3H]U69,593 binding to all three cell lines. Stimulation of low-Km GTPase activity by the kappa-selective agonist (-)U50,488 was greatest in R1.G1 membranes, followed by R1EGO and R1.1. The maximal inhibition of forskolin-stimulated adenylyl cyclase activity by (-)U50,488 was 66 +/- 2% in R1.G1 and 49 +/- 2% in R1EGO, compared with 37 +/- 1% in R1.1 membranes. Whereas maximal inhibition of adenylyl cyclase activity did not correlate with receptor number among cell lines, the inhibition of cyclic AMP production did correlate with stimulation of low-Km GTPase activity. The R1.1 cell line and its derivatives, R1.G1 and R1EGO, express a similar type of kappa opioid receptor, which exhibits differences in coupling to G-proteins and to adenylyl cyclase among cell lines. These cell lines provide an excellent model system for studying the regulation of opioid receptor-adenylyl cyclase coupling efficiency.