Immunoreactivity for the human hematopoietic progenitor cell antigen (CD34) in lipomatous tumors

The human hematopoietic progenitor cell antigen (CD34) recently was shown to react with a variety of nonhematopoietic tissues and their tumors, including vascular endothelium, dendritic interstitial fibroblastic cells, and endoneurial cells as well as with the neoplastic cells in a variety of mesenchymal neoplasms of unknown etiology, such as Kaposi's sarcoma, dermatofibrosarcoma protuberans, epithelioid sarcoma, gastrointestinal stromal tumors, and solitary fibrous tumors. Additionally, it has been claimed that normal adipocytes may also react with this antibody. We studied a series of 90 lipomatous lesions to examine the pattern of immunoreactivity of the CD34 antigen in adipose tissue neoplasms. The study included 14 lipomas, 19 angiolipomas, 4 atypical lipomas, 18 spindle cell lipomas, 3 renal angiomyolipomas, 1 intramuscular lipoma, and 31 liposarcomas. Immunostains identified a network of CD34+ spindle cells admixed with the adipose tissue elements in all cases of lipoma, angiolipoma, angiomyolipoma, intramuscular lipoma, and well-differentiated lipoma-like liposarcoma. Additionally, the spindle cell component in all cases of spindle cell lipoma were strongly positive for this antigen. Atypical, stellate spindle cells and multinucleated "floret" cells in all cases of atypical lipoma as well as in six of 12 cases of well-differentiated lipoma-like liposarcoma of deep soft tissue were also positive for CD34. Scattered spindle cells in all cases of myxoid liposarcoma and in one case of round cell liposarcoma, as well as the sarcomatous component in one case of "dedifferentiated" liposarcoma, were strongly positive for this antigen. The round cells in myxoid liposarcoma and round cell liposarcoma, the signet-ring and multivacuolated lipoblasts in well-differentiated liposarcoma, and the pleomorphic atypical cells in pleomorphic liposarcoma were uniformly negative. The results of this study appear to indicate that lipomatous tumors may harbor a population of CD34+ interstitial dendritic spindle cells. Overgrowth or clonal expansion of this dendritic cell subpopulation may account for the development of spindle cell lipomas and for the spindle cell component in some cases of "dedifferentiated" liposarcoma.

Effect of colchiceine and ursodeoxycholic acid on hepatocyte and erythrocyte membranes and liver histology in experimentally induced carbon tetrachloride cirrhosis in rats

Colchiceine and ursodeoxycholic acid (UDCA) are drugs currently in use as therapy for different types of liver damage. We evaluated their ability to reverse the damage induced by carbon tetrachloride (CCl4) in rats. Six groups were analysed: (1) CCl4 (0.4 g kg(-1), i.p., three times a week) for 13 weeks; (2) CCl4 for 8 weeks followed by colchiceine (60 microg kg(-1)) + CCl4 for 5 weeks; (3) CCl4 for 8 weeks and thereafter UDCA (25 mg kg(-1)) + CCl4 for 5 weeks. Groups 4, 5 and 6 were appropriate controls of colchiceine, UDCA and vehicles respectively. Na+,K+- and Ca2+-ATPase activities and the cholesterol-phospholipid (CH/PL) ratio from erythrocyte and hepatocyte membranes were quantified. Membrane enzymatic activities and CH/PL ratios were affected more in group 1 than groups 2 and 3. We concluded that colchiceine and UDCA were effective drugs in this model of liver damage.

The oncocytic variant of papillary carcinoma of the thyroid: a clinicopathologic study of 15 cases

The oncocytic variant of papillary carcinoma of the thyroid represents an unusual neoplasm whose clinicopathological features and biological behavior have not been thoroughly characterized. We studied 15 cases of thyroid tumors predominantly composed of oncocytic (oxyphilic) cells that were characterized by showing the classical nuclear features of papillary carcinoma of the thyroid. Thirteen patients were women, and two were men; their ages ranged from 34 to 86 years. The tumors measured from 1 to 4 cm in diameter and were well circumscribed and confined to the thyroid gland in all cases except for one, in whom there was extrathyroidal local extension. Histologically, all tumors showed, at least focally, the formation of papillary structures; in 13 cases the papillary features were found to predominate or were admixed in equal proportion with a follicular pattern of growth, and in two the follicular growth pattern predominated and only abortive, small papillary structures could be found on extensive search. In all cases, the classical optically clear nuclei of papillary carcinoma were present throughout the lesions. Nuclear grooves and intranuclear cytoplasmic inclusions were also a prominent and constant component of these lesions. In 13 cases, the tumors showed the features of Hashimoto's or lymphocytic thyroiditis in the surrounding, uninvolved thyroid parenchyma. Follow-up of 1.2 to 13 years (median, 4.5 years) showed the development of cervical lymph node metastases 9 months after surgery in one case; the remainder of patients were alive and free of disease. Oncocytic papillary carcinoma seems to represent a distinctive morphological variant of carcinoma of the thyroid that in our experience does not appear to behave more aggressively than conventional papillary carcinoma. The frequent association of these tumors with autoimmune thyroiditis raises the possibility that the oncocytic changes may be pathogenetically related with the latter process. These tumors should be distinguished from benign and malignant Hurthle cell tumors and other oncocytic thyroid neoplasms that may follow a different biological behavior.

Primary thymic epithelial neoplasms showing combined features of thymoma and thymic carcinoma. A clinicopathologic study of 22 cases

Thymic epithelial neoplasms are unusual tumors that may span the gamut from clinically benign, well-differentiated lesions (encapsulated thymoma) to overtly malignant, poorly differentiated neoplasms (thymic carcinoma). It has been commonly believed that lesions displaying obvious cytologic features of malignancy (i.e., thymic carcinoma) represent a unique and separate group that is histogenetically distinct from thymoma. We have studied 22 cases of thymic epithelial neoplasms characterized by the admixture of areas displaying conventional features of thymoma with areas showing features of thymic carcinoma. The tumors occurred in six women and 16 men whose ages ranged from 23 to 83 years (median, 53). The lesions presented in eight patients with symptoms of chest discomfort resulting from the involvement of surrounding structures; in 14 patients, they were asymptomatic and discovered incidentally on routine chest radiographs. Histologically, most tumors showed a combination of conventional thymomatous elements with well-differentiated squamous-cell carcinoma (10 cases), followed by thymoma and poorly-differentiated squamous carcinoma (seven cases) and spindle-cell thymoma with poorly-differentiated squamous carcinoma (five cases). Areas of transition between the two different components could be identified in most cases. In five cases, areas showing the features of clear-cell carcinoma could be seen either arising from squamous carcinomatous elements or within the thymomatous component, and in one case transitions between lymphoepithelioma-like carcinoma and anaplastic carcinoma could be observed. Two patients had a history of myasthenia gravis with biopsy-proven thymomas in whom the tumors had been monitored without treatment for 10 and 14 years before the sudden enlargement of the mass. The resected specimens in both patients showed the emergence of a carcinoma arising from a thymoma. The present cases appear to support the existence of a continuum in the spectrum of differentiation between thymoma and thymic carcinoma, suggesting a close histogenetic relationship between these two conditions. Such findings are important not only for our understanding of these tumors but may also play a significant role in the assessment of the biologic behavior and management of these lesions.

Gastrointestinal stromal tumors

Stromal tumors of the gastrointestinal tract represent relatively rare lesions that are thought to arise from connective tissue elements located along the entire length of the gut. For many years these tumors have been the subject of much controversy and debate in the literature regarding their histogenesis, criteria for diagnosis, prognostic features, and nomenclature. Only a minority of these lesions, mainly those confined to the esophagus and rectum, have been shown to correspond to mature, well-differentiated types of neoplasms such as leiomyoma or leiomyosarcoma of the conventional type. The majority of stromal tumors of the gastrointestinal tract correspond to a heterogeneous group of lesions that have as their common denominator an immature proliferation of epithelioid or spindle cells arising from its muscle layer and showing partial or incomplete myoid, neural, ganglionic, or mixed features of differentiation. This review will attempt to summarize our current knowledge and understanding of these lesions based on review of the literature and the author's personal experience, with an analysis of the criteria for distinguishing between benign and malignant tumors, and a proposal for a working classification for these lesions.

Primary mediastinal and testicular seminomas: a comparison of K-ras-2 gene sequence and p53 immunoperoxidase analysis of 26 cases

Primary mediastinal seminomas (MS) are rare tumors. Histologically, they are similar to their counterpart in the gonads. The survival rate has varied from 50% to 85% in different series. However, large series of these tumors primarily in the mediastinum are lacking. At the molecular level, a few reports document K-ras mutations in up to 40% of testicular seminomas (TS), localized predominantly to codon 12. Reports on TS p53 immunohistochemistry (IHC) range from negative to overexpression approaching 90% of cases, and by sequence analysis one small series showed a 23% mutation rate. To date, no analyses have been performed for either K-ras mutations or p53 immunohistochemical expression in primary MS. The authors studied 13 cases each of primary MS and TS from archival formalin-fixed, paraffin-embedded sections in which adequate tumor sampling and clinical history, including serological studies, and histological, histochemical, and IHC staining, were performed to confirm the diagnosis. p53 immunoperoxidase staining using citrate buffer/microwave antigen retrieval was performed. Topographic genotyping was performed on 5-microns-thick tissue sections up to 17 years old, in which the neoplastic cell population was sampled. Additionally, multiple sites within a given cases were sampled to determine clonality of the tumor cell population. Polymerase chain reaction and subsequent sequence analysis of the K-ras-2 exon-1 gene was used for mutation analysis. Focal weak staining with p53 IHC was observed in 4 of 13 (31%) MS and 10 of 13 (77%) TS cases, with all remaining cases being negative (P < .05). Only one MS case (8%) showed K-ras mutation (codon 13 GGC > GAC; glycine > aspartate), which is in contrast to 2 of the TS cases (15%), showing codon 12 mutations. All the remaining cases were wild type. Therefore, primary mediastinal seminomas appear to be different in their K-ras sequence and p53 immunostain profile from TS. Codon mutation type may be useful in determining primary versus metastatic origin of a mediastinal seminoma.

Gastrointestinal stromal tumors with prominent signet-ring cell features

Three cases of gastrointestinal stromal tumors characterized by a population of cells displaying prominent signet-ring cell features are described. The tumors occurred in women aged 45 to 74 years and presented as small (< 2.5 cm), well-circumscribed, serosal nodules located within the wall of the stomach, small bowel, and rectum. Histologically, the lesions were characterized by a proliferation of large, round-to-oval cells containing abundant clear cytoplasm with displacement of the nuclei toward the periphery, which imparted to them a striking signet-ring cell configuration. In some areas, the signet-ring cells were seen to merge with short fascicles of spindle cells, whereas in other areas, the tumor cells were associated with prominent deposition of myxoid matrix. Histochemical studies showed glycogen granules within the cytoplasm of the tumor cells in two cases. Immunohistochemical studies showed a heterogeneous pattern of staining, with strong positivity for actin, vimentin, and CD34 in one case; strong vimentin and S-100 protein and weak, focal positivity for actin and CD34 in another; and vimentin positivity alone in the third. The present cases illustrate an unusual morphologic appearance of gastrointestinal stromal tumors that should be distinguished from primary and metastatic mucin-secreting carcinoma and other types of neoplasms with clear cell or signet-ring cell features.

Microglandular carcinoma of the pancreas: immunohistochemical and ultrastructural study of an unusual variant of pancreatic carcinoma that may closely resemble a neuroendocrine neoplasm

Two cases are described of an unusual form of primary adenocarcinoma of the pancreas characterized histologically by their striking resemblance with a neuroendocrine neoplasm. The tumors were composed of a population of relatively small, uniform cells arranged in sheets admixed with small microglandular structures resulting in a cribriform pattern of growth. The tumor cells displayed scant cytoplasm with indistinct cell borders and round to oval nuclei with irregular clumping of chromatin and small, inconspicuous nucleoli. Immunohistochemical studies in both cases showed positivity of the neoplastic cells with CAM 5.2 antibodies and negative staining with a battery of neuroendocrine-related markers including chromogranin, NSE and synaptophysin, as well as with a variety of peptide hormones including insulin, glucagon, vasoactive intestinal polypeptide, gastrin and serotonin. Ultrastructural examination revealed a cohesive population of cells forming abortive glandular lumens lined by imperfectly formed microvilli and showing well-developed junctional complexes. No dense core neurosecretory granules or zymogen granules could be identified in any of the cells, supporting a ductal type of differentiation for these tumors. The main importance of recognizing this rare variant of pancreatic adenocarcinoma lies in avoiding misdiagnosis with other primary and metastatic neuroendocrine neoplasms of this organ. Immunohistochemical and ultrastructural examination will be of value in such cases for differential diagnosis.

Benign cutaneous adnexal tumors with combined folliculosebaceous, apocrine, and eccrine differentiation. Clinicopathologic and immunohistochemical study of eight cases

Benign cutaneous adnexal tumors displaying divergent differentiation are rare, with very few well-documented cases reported in the literature. We describe eight cases of benign adnexal tumors showing a variable combination of eccrine, apocrine, and folliculosebaceous differentiation. Clinically, all tumors presented as solitary, slowly enlarging dermal or subcutaneous nodules located in the head and neck and the extremities. Histologically, they were characterized by well-circumscribed, unencapsulated nodules composed of a lobular proliferation of epithelial cells displaying a spectrum of trichogenic, sebaceous, apocrine, and eccrine differentiation. The histological spectrum included lobules and trabeculae of basaloid cells with glandular and ductal elements, well-formed folliculosebaceous units, primitive follicles, and foci of tricholemmal keratinization. Immunohistochemical evaluation in four cases showed similar cytokeratin, carcinoembryonic antigen, and epithelial membrane antigen staining profiles as those reported for sweat gland adenomas; in addition, focal S-100 protein positivity and GCDFP-15 positivity could also be demonstrated, suggesting eccrine-apocrine differentiation. The tumors were most frequently confused histologically with other adnexal neoplasms, including sebaceoma, sebaceous adenoma, basal cell carcinoma, chondroid syringoma, and trichoepithelioma. The present series highlights the capability.

Pleomorphic large cell lymphomas of the mediastinum

Nine cases of primary non-lymphoblastic, non-Hodgkin's large cell lymphomas of the mediastinum characterized by a highly pleomorphic histologic appearance are described. The patients, four women and five men, were aged 30 to 65 years. All patients presented with symptoms referable to their tumors, including cough, chest pain, dyspnea, pleural effusion, and superior vena cava syndrome. Clinical and pathologic staging in all patients showed that the bulk of the tumor was confined to the chest cavity at the time of initial diagnosis, with local infiltration into the neck, lung hilum, and surrounding mediastinal structures. Three different histological growth patterns were observed: one composed of a diffuse proliferation of pleomorphic, highly atypical cells with bizarre nuclear features that closely resembled a high grade sarcoma; another one composed of sheets of large, epithelial-appearing atypical cells suggestive of anaplastic carcinoma; and another pattern characterized by a pleomorphic proliferation of large lymphoid cells admixed with numerous scattered Reed-Sternberg-like cells reminiscent of the lymphocyte-depleted variant of Hodgkin's disease. Immunohistochemical studies on paraffin-embedded tissue sections in all cases showed positive staining of the tumor cells with CD20 and CD45 antibodies and negative staining with a large panel of markers, including broad-spectrum keratin, CAM 5.2, carcinoembryonic antigen, epithelial membrane antigen, vimentin, actin, desmin, HMB 45, S-100 protein, CD3, CD15, CD30, and CD45RO. Because of their location restricted to the anterior mediastinum, frequent lack of recognizable lymph node architecture, and bizarre cytologic features, the present group of lesions posed difficulties for diagnosis, their correct identification was achieved through the application of a panel of immunohistochemical markers. An awareness of these unusual histologic appearances of primary large cell lymphoma in the mediastinum and inclusion of a broad panel of lymphoid markers are therefore recommended for the evaluation of pleomorphic, undifferentiated malignant neoplasms of this anatomic region.

Clear cell tumors of the skin

Clear cell tumors of the skin represent a heterogeneous group of lesions of diverse histogenesis that share as their common denominator the presence of cells containing abundant clear cytoplasm. The phenomenon of cytoplasmic clearing may be observed focally or represent the dominant feature in a variety of tumors originating from the epidermis or in tumors within the dermis showing well-defined features of eccrine, sebaceous, and follicular lines of differentiation. In addition to the aforementioned conditions, melanocytic lesions derived from the epidermis characterized by a prominent or predominant clear cell component as well as metastases to the skin from clear cell tumors of internal organs may enter the differential diagnosis and will also be discussed. Because of the superficial resemblance imparted by this distinctive cytologic feature, these lesions may occasionally pose difficulties for diagnosis. A review of the various entities that comprise this group of lesions is presented, with emphasis on their distinguishing histopathologic features and differential diagnosis.

The down-regulated in adenoma (DRA) gene encodes an intestine-specific membrane glycoprotein

The protein product of the DRA gene, a gene whose expression is down-regulated in colon adenomas and adenocarcinomas, is a membrane glycoprotein and a member of a family of sulfate transporters. It is expressed in the intestinal tract (duodenum, ileum, cecum, distal colon), but not in the esophagus or stomach. DRA mRNA expression is restricted to the mucosal epithelium, and DRA protein expression is further limited to the columnar epithelial cells, particularly to the brush border. Consistent with its expression in the differentiated columnar epithelium of the adult human colon, DRA is first expressed in the midgut of developing mouse embryos at day 16.5, corresponding with the time of differentiation of the epithelium of the small intestine. A model for the structure of the DRA protein is proposed and its possible role in colon tumorigenesis is discussed.

Chordomas of the mediastinum: clinicopathologic, immunohistochemical, and ultrastructural study of six cases presenting as posterior mediastinal masses

Six cases of chordomas presenting as primary posterior mediastinal tumors are described. Three patients were female, and three were male between the ages of 8 and 65 years (mean, 40.6 years). In all cases, the tumors presented radiographically as relatively well-circumscribed, encapsulated soft tissue masses that did not seem to be related to the thoracic or dorsal spine. Only in one case, focal infiltration of bone at the level of T6-T7 was observed at the time of surgery. Histologically, the lesions showed a spectrum of features that ranged from sheets and cords of large cells with abundant vacuolated cytoplasm to small, stellate cells embedded within an abundant mucoid matrix. In one case, the cell population showed more pronounced nuclear atypia with loss of cytoplasmic vacuolization, frequent mitotic figures, necrosis, and solid areas characterized by a perivascular distribution of atypical spindle cells set against a myxoid stroma. Another case showed features of chondroid chordoma, with an immature chondroid-appearing matrix surrounding the atypical tumor cells. Immunohistochemical studies in all cases showed positive staining of the tumor cells with CAM 5.2 and broad-spectrum keratin, epithelial membrane antigen (EMA) and vimentin, and, to a lesser extent, with S-100 protein. Stains for muscle actin, carcinoembryonic antigen (CEA), and desmin were negative. Ultrastructural examination in two cases showed a spectrum of features that varied from large cells with abundant cytoplasm containing scattered ribosomes, glycogen granules, Golgi apparatti, abundant intermediate filaments, and small lumen formation with immature microvilli to smaller cells with elongated cytoplasmic processes, fewer intermediate filaments, rare desmosome type intercellular junctions, and complexes of mitochondria/rough endoplasmic reticulum. On clinical follow-up, two patients died with metastases to the lungs, chest wall, and liver from 1 to 3 years after diagnosis, and two patients are alive and well without evidence of disease after 3 and 16 years. Chordoma should be entertained in the differential diagnosis of posterior mediastinal tumors. Application of immunohistochemical stains or electron microscopy will be of aid in separating them from other conditions that may histologically closely resemble these lesions.

Clear nuclear changes in Hashimoto's thyroiditis. A clinicopathologic study of 12 cases

Histologic sections of thyroid glands resected from 12 patients with Hashimoto's thyroiditis have been studied in which areas were present showing clear nuclear changes such as those seen in papillary carcinoma. The patients' ages ranged from 28 to 78 years (mean = 57.3); 11 were women and one was a man. The lesions presented as focal, ill-defined areas displaying clear nuclear changes of the cells within otherwise well-circumscribed adenomatous nodules, or as small clusters of cells showing the characteristic clear nuclear features randomly admixed with the Hashimoto's elements. Histologically, the lesions were characterized by a range of nuclear features that included optically clear nuclei, prominent cytoplasmic invaginations with intranuclear cytoplasmic inclusions, and occasional nuclear grooves. In two cases, focal papillary formations were seen that were lined by cells with optically clear nuclei. In two other cases, well-circumscribed nodules bearing the architectural features of trabecular hyalinizing adenoma with focal clear nuclear changes were also present. In three cases, small (< 0.5 cm) well-circumscribed nodules bearing cytological features indistinguishable from those of microscopic papillary carcinoma were also present in addition to the areas of clear nuclear change. Follow-up of 1.5 to 19 years (mean = 9 years) showed no evidence of recurrence or metastases in any of our patients. Our study appears to indicate that thyroid follicular epithelium in patients with Hashimoto's thyroiditis may exhibit a range of clear nuclear changes similar to those encountered in papillary carcinoma. Such changes may represent another form of response of follicular epithelium to the underlying autoimmune process with possible premalignant connotation. However, they should be interpreted in context with the rest of the findings within the involved gland to avoid an overdiagnosis of malignancy.

Thymic carcinoid with prominent mucinous stroma. Report of a distinctive morphologic variant of thymic neuroendocrine neoplasm

Four cases are described of a distinctive morphologic variant of thymic carcinoid that was characterized by abundant stromal mucin admixed with the neuroendocrine elements resulting in a histologic picture reminiscent of metastatic mucin-secreting carcinoma. The patients were three men and a woman, aged 22 to 43 years. The tumors presented with symptoms of chest discomfort, cough, and dyspnea and were described as large anterior mediastinal masses on chest radiographs and computerized scans. Histologically, all cases showed nests and strands of tumor cells embedded in an abundant lightly eosinophilic, mucinous stroma with small cellular clusters as well as scattered single tumor cells seen floating in the mucin. The mucinous matrix was negative for periodic acid Schiff's and mucicarmine stains; alcian blue stains at pH 2.5 showed strong positivity of the mucinous material; this reaction was abolished by treatment with hyaluronidase, indicating the presence of nonepithelial stromal mucosubstances. Immunohistochemical stains showed strong positivity of the tumor cells with CAM 5.2, chromogranin, synaptophysin, and neuron-specific enolase, and negative staining with carcinoembyronic antigen and epithelial membrane antigen. Electron microscopy done in one case showed abundant dense-core cytoplasmic neurosecretory granules; there was no evidence of glandular secretory activity by the tumor cells. The tumors in two patients behaved in a highly aggressive fashion, with invasion of the chest wall, recurrence, and metastases to the lungs, pleura, and axillary, retroperitoneal, and mesenteric lymph nodes. Thymic carcinoid should be considered in the differential diagnosis of mediastinal neoplasms displaying prominent mucinous features. Application of immunostains and electron microscopy will be of value for establishing the correct diagnosis in this setting.

Solitary fibrous tumors of soft tissue. A clinicopathologic and immunohistochemical study of 12 cases

We describe 12 cases of primary soft tissue neoplasms that showed the histologic and immunohistochemical features of solitary fibrous tumors of serosal surfaces (solitary fibrous mesothelioma, submesothelial fibroma). Nine patients were women and three were men whose ages ranged from 28 to 83 years. Seven lesions were located in the head and neck region, and the remainder were located in the back, buttock, perineum, and groin. The lesions measured from 1 to 6 cm in greatest diameter and presented grossly as well-circumscribed, unencapsulated, soft to rubbery tissue masses. Histologically they were characterized by a proliferation of spindle cells exhibiting a variety of growth patterns, including storiform, herringbone, neural with wavy nuclei, and hemangiopericytic admixed with areas of sclerosis. In two cases the lesions showed areas of increased cellularity with occasionally scattered mitotic figures. Three cases were located adjacent to a major salivary gland; in one, entrapment of normal salivary gland acini and ducts could be observed at the edges of the lesion. Immunohistochemical studies showed positive staining of the spindle cells with CD34 (anti-HPCA-1) and vimentin antibodies and negative staining with keratin, actin, desmin, S-100 protein, collagen type IV, and factor VIII related antigen. Follow-up from 6 months to 12 years has shown no evidence of recurrence or metastasis in any of our patients. Solitary fibrous tumors appear to represent ubiquitous mesenchymal neoplasms that may not be necessarily restricted to serosal surfaces. Identification of these lesions is of importance to avoid misdiagnosis with other more aggressive conditions in soft tissue locations.

Ectopic poorly differentiated (insular) carcinoma of the thyroid. Report of a case presenting as an anterior mediastinal mass

A case is presented of an anterior mediastinal mass arising in a 64-year-old woman that showed on histologic, immunopathologic, and ultra-structural examination features of a poorly differentiated (insular) thyroid carcinoma. The tumor in this patient most likely arose from ectopically displaced thyroid tissue on the basis of a developmental defect. The clinicopathologic features and differential diagnosis of the lesion in the setting of its mediastinal location are discussed. Ectopic poorly differentiated (insular) carcinoma of the thyroid should be added to the list of mediastinal tumors showing a solid or insular growth pattern.

Mediastinal seminomas with prominent cystic changes. A clinicopathologic study of 10 cases

We present 10 cases of thymic seminomas associated with prominent cystic changes. All patients were males, aged 16 to 79 years (median, 23.5). Clinically, two patients presented with chest pain/four were asymptomatic and the tumors were discovered on routine chest radiographs; one tumor was discovered incidentally at autopsy; and in three patients no clinical information was obtained. Grossly, the tumors were described as multilocular cystic lesions that ranged in size from 7 to 19 cm in greatest dimension, showing small focal areas of induration within the cyst walls. Histologically, the lesions were characterized by cystic spaces lined by squamous or cuboidal epithelium showing severe chronic inflammatory changes with areas of cholesterol cleft granulomas, lymphoid follicular hyperplasia, and scattered foci of residual thymic parenchyma within the walls of the cysts, resulting in a picture indistinguishable from acquired multilocular thymic cysts. Careful examination, however, revealed microscopic foci composed of a neoplastic proliferation of large polygonal cells with slightly eosinophilic to clear cytoplasm and large nuclei with prominent nucleoli. The atypical cells were admixed with an inflammatory background and were often accompanied by a florid granulomatous reaction. Periodic acid-Schiff histochemical reaction with diastase revealed moderate amounts of glycogen within the cytoplasm of the tumor cells. Immunohistochemical studies in five cases showed positive labeling of the tumor cells with placental alkaline phosphatase. Nine patients were treated by complete surgical excision of the mass, and additional postoperative radiation therapy was given to two patients. Follow-up information available for five patients showed all to be alive and well from 2 to 19 years after diagnosis (mean follow-up, 9 years). Four of the patients were lost to follow-up. The pathogenesis of the cystic process in these cases remained unsettled but may represent a reactive change secondary to epithelial hyperplasia of thymic epithelium. Thymic seminoma should be considered in the differential diagnosis of cystic lesions of the anterior mediastinum; extensive sampling of such lesions is therefore recommended for proper evaluation.

Smooth muscle tumours presenting as pleural neoplasms

Five smooth muscle tumours presenting as pleural neoplasma are presented. The patients were three women and two men aged between 21 and 69 years (mean = 45 years). Clinically, one patient presented with chest pain, one with empyema and the other three were asymptomatic. Two of the tumours were located in the left side of the chest cavity and three in the right side. In four cases, the lesions presented as solitary pleural-based masses that varied in size from 10-18 cm in greatest dimension: in two of these cases, involvement of the diaphragm was present in addition to the pleural involvement. In one case, the tumour was seen to totally encase the right lung simulating the growth pattern of malignant mesothelioma. Histologically, three cases displayed an atypical spindle cell proliferation with marked cellular pleomorphism, mitoses and areas of hemorrhage and necrosis. The other two cases were characterized by a bland-appearing smooth muscle proliferation of uncertain malignant potential composed of elongated cells with a moderate amount of eosinophilic cytoplasm and cigar-shaped nuclei, lacking significant nuclear pleomorphism or mitotic activity. Immunohistochemical studies showed strong positivity for alpha-smooth muscle actin in all cases, and for desmin in four of five cases, and a focal positive reaction for keratin in one case. Ultrastructural examination in one of the high-grade tumours showed features of smooth muscle differentiation. Three of the patients were treated by complete surgical excision while, in the other two patients, the lesions were incompletely resected.(ABSTRACT TRUNCATED AT 250 WORDS)

Thymolipoma: clinicopathologic review of 33 cases

The clinical, radiologic, and pathologic features of 33 cases of mediastinal thymolipoma are presented. The patients' ages ranged from 2 to 64 (mean, 33) years; 18 were male and 15 were female. Clinically, the majority of patients (18 cases) were asymptomatic. Five patients presented with upper respiratory symptoms, two patients presented with chest pain, two patients with myasthenia gravis, and one patient with a neck mass; no clinical information was available in four patients. All the tumors were located in the anterior mediastinum and in all cases complete surgical resection of the mass was accomplished. Radiographically, 20 cases showed an anterior mediastinal tumor; when available, computed tomography and/or magnetic resonance imaging demonstrated a mixture of fat and soft tissue elements in these tumors. Grossly, the tumors were described as fairly well-circumscribed, soft, yellowish, fatty tumors with focal solid areas. The tumors varied in size from 4.5 to 36 cm in greatest dimension. Histologically, they were characterized by the presence of abundant mature adipose tissue admixed with areas containing remnants of thymic tissue. The fatty tissue consisted of mature adipocytes devoid of atypia, and the thymic tissue component varied from strands of atrophic thymic epithelium to large areas containing thymic parenchyma showing the typical mixed epithelial/lymphocytic architecture with numerous Hassall's corpuscles. Areas of calcification and cystic degeneration of Hassall's corpuscles were quite prominent in a large number of cases. Our study shows that thymolipomas span the age ranges from the very young to adult individuals with a slight prevalence for patients under the age of 40.(ABSTRACT TRUNCATED AT 250 WORDS)

Primary pulmonary rhabdomyosarcomas: a clinicopathologic and immunohistochemical study of three cases

Three cases of primary pulmonary rhabdomyosarcoma in adults are presented. The patients were all men between the ages of 57 and 78 yr (mean 67.5). All patients presented with symptoms referable to their tumors, including cough, shortness of breath, pleuritic chest pain, and weight loss. In one patient, a history of tobacco and alcohol abuse was obtained. Anatomically, two tumors were located in the left upper lobe and one in the left lower lobe. Grossly, the tumors ranged in size from 6 to 11.5 cm and were tan-gray, firm masses with areas of necrosis and hemorrhage. Histologically, the tumors were characterized by a spindle cell proliferation admixed with areas showing a pleomorphic cell population with numerous rhabdomyoblasts and areas of hemorrhage and necrosis. Immunohistochemically, all three tumors showed strong positivity with desmin and myoglobin antibodies and negative staining with antibodies against keratin, epithelial membrane antigen, and S-100 protein. All patients had a fatal outcome. Two patients died a few days after admission with respiratory distress; the third one died 2 years after diagnosis with widely metastatic disease. Autopsy findings in all cases disclosed disseminated metastases to multiple abdominal and thoracic organs. Primary pulmonary rhabdomyosarcoma should be considered in the differential diagnosis of poorly differentiated pulmonary neoplasms in adults and should be distinguished from other primary and metastatic sarcomas.

Mucoepidermoid carcinomas of the thymus. A clinicopathologic study of six cases

Six cases of mucoepidermoid carcinoma of the thymus are presented. The patients were two men and four women aged 17 to 66 years (median age, 34.5). Clinically, three patients had symptoms of chest discomfort and three were asymptomatic. Grossly, the tumors in three patients were described as cystic structures varying in size from 7 to 8 cm in greatest dimension, with focal areas of induration within the walls of the cyst that averaged from 1.5 to 3 cm. The other three cases had grossly and radiographically well-circumscribed, homogeneous tumor masses. Histologically, the lesions showed a spectrum of features that ranged from those of well-differentiated, to moderately well-differentiated, to poorly differentiated mucoepidermoid carcinoma, with sheets and solid islands of squamoid cells admixed with mucin-secreting epithelium lining gland-like spaces. In four cases, the tumor was histologically seen in continuity with the epithelial lining of multilocular cystic structures; the nonneoplastic components of the cysts contained abundant inflammation and showed the features of otherwise conventional acquired multilocular thymic cysts. Clinical follow-up showed that the two patients with intermediate and high-grade tumors died within 2 and 7 months after initial diagnosis. One of these patients showed at autopsy residual tumor limited to the mediastinum, whereas the other patient died with metastases to pericardium and myocardium despite postoperative radiation therapy. Two patients with low-grade tumors were alive and well with no residual disease 2 and 3 years after surgery, and the other two were lost to follow-up. Mucoepidermoid carcinoma of the thymus should be included in the differential diagnosis of cystic neoplasms of the thymus. As with their counterparts at other sites, the biologic behavior of these tumors closely correlates with their degree of differentiation and amount of cytologic atypia.

Primary pulmonary sarcomas with features of monophasic synovial sarcoma: a clinicopathological, immunohistochemical, and ultrastructural study of 25 cases

We present 25 cases of a primary pulmonary sarcoma bearing histological, immunohistochemical, and ultrastructural features indistinguishable from those of monophasic synovial sarcoma of soft tissue. The patients were 11 men and 14 women between the ages of 16 and 77 years. Clinically, the most common symptoms were chest pain, cough, shortness of breath, and hemoptysis. The lesions involved all lung segments. Grossly, they varied in size from 0.6 to 20 cm and were described as soft to rubbery tumors with areas of necrosis and hemorrhage, some with cystic changes. Two lesions involved the bronchial wall and in one case the tumor was described as encircling the bronchial tree. Histologically, all of the lesions were characterized by an atypical spindle cell proliferation with a solid growth pattern. Areas of myxoid, neural, hemangiopericytic, and epithelial-like growth pattern were observed. Mitoses, necrosis, and hemorrhage were seen in all lesions in varying proportions. Immunohistochemical studies for epithelial membrane antigen (EMA) and keratin showed strong focal positivity in 25 of 25 and 23 of 25 lesions, respectively. Immunohistochemical study for vimentin showed diffuse strong positivity in all lesions. Other immunostains, including desmin, smooth muscle actin, and S-100 protein, were negative. Electron microscopy in three cases showed spindle cells with elongated nuclei containing abundant cytoplasmic rough endoplasmic reticulum and well developed desmosome type intercellular junctions. Follow-up information ranging from 2 to 20 years was obtained in 18 patients. Six patients died of their tumors, whereas four patients died of unrelated causes without evidence of recurrence or metastases. Eight patients were alive with disease (recurrence and/or metastases) from 1 to 7 years after diagnosis. Four patients were alive and well without evidence of recurrence or metastases from 2 to 20 years (mean follow-up, 12.5 years). The present group of lesions appears to constitute a distinctive and as yet previously undescribed primary sarcoma of the lung, which probably represents the visceral counterpart of monophasic synovial sarcoma of soft tissue in a pulmonary location. Because of their distinctive biology these lesions should be distinguished from a variety of primary and metastatic malignancies of the lung.

Malignant mixed epithelial/mesenchymal neoplasms of the lung

The existence of biphasic neoplasms occurring primarily in the lung is a well-known albeit rare event. The spectrum of malignant tumors displaying a mixed epithelial/mesenchymal growth pattern is rather narrow when these tumors occur primarily in the lung. The two most often encountered neoplasms showing features of epithelial and mesenchymal differentiation are carcinosarcomas and pulmonary blastomas. Tumors with analogous features are of ubiquitous distribution in the human body and have been described in numerous other organs, including the gastrointestinal tract, the genitourinary tract, and the endocrine system. Although the histopathologic features of these tumors may seem simple in most cases, there appear to be numerous pitfalls in their diagnosis; gray areas still remain in the characterization of these tumors, because a certain degree of overlap may be encountered with these two conditions. Such problems are understandable because the incidence of these tumors in the general population is very rare. Therefore, one is expected to find divergent points of view regarding these neoplasms. It is of importance, however, to unify criteria not only for diagnostic purposes, but also to determine the prevalence and behavior of these neoplasms, because such information may provide a rationale for adjustment and improvement in the treatment and diagnosis of these unusual neoplasms. We will review past and current concepts regarding these unusual tumors, as well as their more salient histopathologic features.