Primary large-cell lymphomas of the mediastinum

The mediastinum is a frequent site of involvement for malignant lymphoma. The most common types encountered in this location include Hodgkin's and non-Hodgkin's lymphoma and lymphoblastic lymphoma. With the exception of lymphoblastic lymphoma in children and adolescents, most cases of mediastinal involvement by lymphoma represent part of systemic disease and do not generally pose difficulties for diagnosis. However, a relatively small group of tumors have become increasingly recognized in recent years that are primarily localized in the anterior mediastinum and show features of nonlymphoblastic/non-Hodgkin's large-cell lymphoma. Because such tumors are capable of adopting unusual morphological appearances, they can often pose difficulties for diagnosis and be frequently mistaken for other conditions. This review discusses this group of neoplasms collectively known as diffuse large-cell lymphoma of the mediastinum. The clinicopathologic, immunohistochemical, and molecular genetic aspects of these tumors appear to indicate that a significant proportion of them may correspond to a distinctive type of lymphoproliferative process most likely arising from a native B-cell population of the thymus, thus representing, in essence, a primary extranodal large-B-cell lymphoma of the thymus.

Anaplastic large cell lymphoma of the spleen

A case is presented of CD30+ anaplastic large cell lymphoma of the spleen. The patient, a 61 year old woman with a history of chronic lymphocytic leukemia (CLL) was seen for the sudden development of splenomegaly with thrombocytopenia. A splenectomy was performed which showed massive replacement of the spleen by a population of large atypical lymphoid cells showing bizarre nuclear forms and multinucleated tumor cells reminiscent of Reed-Sternberg cells. Immunohistochemical studies showed strong membrane and dot-like paranuclear positivity in the majority of the atypical cells for CD30, with coexpression in many of the cells for CD15. Additionally, the cells also strongly reacted with CD3, UCHL-1, EMA and LCA. The present case illustrates an unusual variant of anaplastic (CD30+) large cell lymphoma sharing histologic and immunophenotypic features that overlap with those of Hodgkin's disease. The history in this patient of CLL with sudden development of splenomegaly raises the possibility of transformation of CLL into a high-grade lymphoma (Richter's syndrome). The possible pathogenetic implications of this phenomenon are discussed.

Germ cell tumors of the mediastinum and testis: a comparative immunohistochemical study of 120 cases

An immunohistochemical study was performed in 120 cases of mediastinal and testicular germ cell tumors from archival, paraffin-embedded material to compare the patterns of expression between the two groups with a panel of markers, including broad-spectrum keratin, CAM 5.2 low-molecular-weight cytokeratin, placental-like alkaline phosphatase (PLAP), alpha-fetoprotein (AFP), human beta-chorionic gonadotropin (hCG), vimentin, and CD30 (Ki-1 antigen). Significant differences were observed between mediastinal and testicular seminomas: mediastinal seminomas showed strong dot-like paranuclear positivity of the tumor cells with antibodies to CAM 5.2 low-molecular-weight keratin in 80% of cases (32 of 40), as compared with only 20% positivity (5 of 24) in testicular seminomas; placental alkaline phosphatase (PLAP) was also found to be less commonly expressed in testicular seminomas (12 of 24) than in mediastinal seminomas (37 of 40); a similar pattern of expression was also observed for vimentin, which was present in scattered tumor cells in a higher proportion of mediastinal seminomas (28 of 40) than in testicular seminomas (11 of 24). The staining pattern and distribution of these markers did not show significant differences between the two groups for the various other tumor categories studied, including yolk sac tumor, embryonal carcinoma, and choriocarcinoma. The tumor cells in both testicular and mediastinal embryonal carcinoma showed strong positivity for the CD30 antigen; however, strong positivity for this marker was also observed in 6 of 25 yolk sac tumors and in scattered individual tumor cells in 4 of 63 seminomas. The results of this study show that significant differences exist between the immunostaining patterns of mediastinal and testicular seminomas, suggesting that the former may be characterized by a more mature phenotype than their testicular counterparts. Also, CD30 expression may not be necessarily restricted to embryonal carcinomas and occasionally may be observed in yolk sac tumors and seminoma cells, supporting the close histogenetic relationship that exists among these tumor types.

Expression of bcl-2 oncoprotein in benign and malignant spindle cell tumors of soft tissue, skin, serosal surfaces, and gastrointestinal tract

An immunohistochemical study to determine the pattern of immunoreactivity for bcl-2 oncoprotein was performed in 380 spindle cell tumors of soft tissue, skin, serosal surfaces, and gastrointestinal tract. The cases studied included examples of benign, reactive spindle cell proliferations to benign and malignant spindle cell neoplasms, including nodular fasciitis (10), fibromatosis (5), dermatofibroma (10), dermatofibrosarcoma protuberans (18), Kaposi's sarcoma (15), spindle cell lipomatous tumors (24), benign and malignant smooth muscle tumors (35), neural/peripheral nerve sheath neoplasms (53), synovial sarcomas (70) solitary fibrous tumors of serosal surfaces and other sites (56), gastrointestinal stromal tumors (GIST) (47), and malignant undifferentiated fibroblastic spindle cell proliferations of soft tissue (37 cases). The results of bcl-2 staining was additionally correlated with CD34 immunoreactivity. Bcl-2 was uniformly negative in all cases of nodular fasciitis, fibromatosis, and dermatofibroma, as well as in benign and malignant smooth muscle proliferations. Strong positivity for bcl-2 was observed in all cases of spindle cell lipoma, dendritic fibromyxolipoma, Kaposi's sarcoma, solitary fibrous tumors, gastrointestinal stromal tumors, and in the spindle cell component of synovial sarcoma. With the exception of the last, there appeared to be a close correlation between the expression of bcl-2 and CD34 in these tumors. Strong bcl-2 positivity also was found, at least focally, in approximately one third of benign and malignant peripheral nerve sheath tumors, particularly in the better-differentiated (Antoni type A) areas. Sarcomas of fibroblastic type, including low-grade myxofibrosarcoma, malignant fibrous histiocytoma, and fibrosarcoma, showed variable expression of bcl-2 in the tumor cells. Our results appear to indicate that bcl-2 may have a wide distribution among benign and malignant spindle cell neoplasms. Strong expression of this marker in some of these conditions, particularly solitary fibrous tumor, gastrointestinal stromal tumors, and synovial sarcoma, may be of aid for differential diagnosis.

Dendritic fibromyxolipoma: clinicopathologic study of a distinctive benign soft tissue lesion that may be mistaken for a sarcoma

Twelve cases are described of a distinctive benign soft tissue lesion that may be mistaken for a sarcoma. The tumors occurred in 11 men and a woman aged 33 to 81 years (mean, 64 years), and measured from 2 to 11 cm in greatest diameter (mean, 6 cm). They were grossly described as soft, well-circumscribed, yellow-gray, with a mucoid cut surface. All cases were superficially located in the subcutis or muscular fascia of the head and neck region or the chest and back. Histologically, the tumors were characterized by a proliferation of spindle or stellate fibroblastic cells variably admixed with mature adipose tissue embedded in an abundant myxoid and collagenized stroma. The spindle and stellate fibroblastic cells were characterized by slender dendritic prolongations of their cytoplasm, which appeared to extend for short distances along connective tissue planes. Electron microscopy in two cases confirmed the dendritic nature of the fibroblastic cells, which showed elongated cytoplasmic processes lacking external lamina and displaying foci of pinocytotic activity. Immunohistochemical studies in 11 cases showed strong positivity of the spindle cells with vimentin, CD34 and bcl-2, and negative staining for smooth muscle actin, muscle-specific actin (HHF35), desmin, S-100 protein, keratin, and EMA. Because of their prominent myxoid stroma and relatively large size, some of these tumors were initially misinterpreted as low-grade sarcomas. Clinical follow-up in five cases, however, showed that the patients were alive and well without evidence of recurrence between 5 and 13 years (mean follow-up, 8 years) after simple local excision. The present cases appear to represent a distinctive form of benign soft tissue neoplasm that should be distinguished from myxoid liposarcoma and other benign and malignant myxoid tumors of superficial soft tissues.

Germ-cell tumors of the mediastinum

Germ-cell tumors occurring primarily in the mediastinum have been well recognized in the literature for many years. Unfortunately, most of what has been written on these tumors has been in the form of case reports and small series of cases, thus precluding a better understanding of their clinical and demographic features, as well as of their biologic behavior in this particular location. In addition, mediastinal germ-cell tumors not only have never had a standardized nomenclature, but they also have lacked the benefit of a clinical staging scheme for assessment of prognosis. Another important aspect of these tumors that has required attention is the frequency with which teratomatous lesions are associated with malignant components in the mediastinum. Comprehensive studies of mediastinal germ-cell tumors to determine whether these lesions recapitulate the distribution, histopathologic features, and biologic behavior of their counterparts in other areas, such as the gonads, have been lacking for many years. In this article, we review our experience with a large series of cases of primary mediastinal germ cell tumors and examine recent concepts and advances in our understanding of these unusual and diagnostically challenging neoplasms.

Primary alveolar soft-part sarcoma of the mediastinum: a clinicopathological and immunohistochemical study of two cases

AIMS

Primary alveolar soft part sarcomas originating within the thoracic cavity are rare. The cases herein described highlight the ubiquitous distribution of this neoplasm and the importance of considering this tumour in the differential diagnosis of mediastinal tumours.

METHODS AND RESULTS

Two cases of alveolar soft-part sarcoma of the mediastinum are presented. The patients are two men of 22 and 23 years of age. Clinically, the patients presented with symptoms of chest pain. One tumour was in the anterior mediastinum while the second tumour was in the posterior mediastinum. Even though the bulk of the tumours were in mediastinal locations, both patients had pulmonary metastases at the time of diagnosis. Histologically, both tumours showed the classic morphology of alveolar soft part sarcoma, i.e. a proliferation of large polygonal cells with round to oval nuclei, prominent nucleoli and moderate amounts of eosinophilic cytoplasm arranged in a prominent alveolar pattern. Periodic acid-Schiff stains showed the characteristic diastase-resistant intracytoplasmic crystals. Immunohistochemical studies showed focal myoglobin reactivity in one case, while cytokeratin, vimentin, S100 protein, chromogranin, synaptophysin, neurofilaments, leu-enkephalin, desmin, smooth muscle actin and muscle-specific actin were negative in both cases. The patient with the anterior mediastinal tumour died of disease 14 months after diagnosis, and the patient with the posterior mediastinal mass remained well for at least 15 years and was later lost to follow-up.

CONCLUSIONS

As has been observed in other anatomic areas, namely soft tissues, alveolar soft part sarcomas may follow an uncertain natural history. Interestingly, in our cases, the tumour in the anterior mediastinum followed a fatal course raising the possibility that the anatomic location of the tumour may have play a role in the behaviour of the tumour.

Amphicrine medullary carcinoma of the thyroid with luminal differentiation: report of an immunohistochemical and ultrastructural study

A case of amphicrine medullary carcinoma of the thyroid is presented. The patient was an 18-year-old female with nonhereditary MEN IIb, submucosal neuromas in the oral cavity, and a thyroid tumor that metastasized to regional lymph nodes. Histologically the thyroid tumor was composed of polygonal cells arranged in a solid/trabecular pattern admixed with mucus-producing goblet cells and displaying focal cytoplasmic lumen formation. Immunohistochemical stains were positive for calcitonin, carcinoembryonic antigen, and chromogranin. Electron microscopy demonstrated C-cells containing neurosecretory granules as well as intestinal-type microlumina. The presence of goblet cells and intestinal-type microlumina in medullary carcinoma of the thyroid is reminiscent of amphicrine tumors of the gastrointestinal tract and supports the hypothesis that the parafollicular C-cells of the thyroid may be of endodermal derivation.

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.

Hepatoid yolk sac tumors of the mediastinum: a clinicopathologic and immunohistochemical study of four cases

Four cases of primary hepatoid yolk sac tumors of the anterior mediastinum are described. The patients were all men between the ages of 26 and 40 years (median 33). Clinically, they all presented with a history of shortness of breath and chest pain of several weeks' duration. None of the patients had a history of germ cell tumor elsewhere or evidence of any hepatic abnormality. Grossly, all the tumors were described as large mediastinal masses that impinged on adjacent structures. Histologically, they were characterized by sheets of medium-sized, round to polygonal neoplastic cells with moderate amounts of eosinophilic cytoplasm and round to oval nuclei with prominent nucleoli. The cellular proliferation was homogeneous and displayed moderate cellular atypia and scattered mitotic activity. All the tumors showed focally the presence of more conventional areas of yolk sac tumor, with islands of tumor cells showing a reticular pattern of growth admixed with scattered intra- and extracellular hyaline globules and occasional Schiller-Duval bodies. Immunohistochemical studies showed strong positivity of the tumor cells for alpha-fetoprotein in both components of the lesions. Follow-up information was available in three patients, all of whom developed lung metastases within a year after initial diagnosis. Two of these patients died of tumor within the same period, whereas a third patient has been lost to follow-up. The present cases illustrate an unusual histologic pattern of yolk sac tumor in the mediastinum and highlight the importance of considering this tumor in the differential diagnosis of lesions showing a hepatoid pattern of growth in the mediastinal area.

Yolk sac tumors of the mediastinum with prominent spindle cell features: a clinicopathologic study of three cases

Three cases of primary mediastinal yolk sac tumors with prominent spindle cell features are presented. The patients were three men 24-34 years of age (mean 29). Clinically, two patients presented with symptoms of chest pain and cough; no clinical information was provided for the third patient. Grossly, the tumors were described as large mediastinal masses, with a hemorrhagic and necrotic cut surface. Histologically, the tumors were characterized by a predominantly atypical spindle cell proliferation admixed with areas that showed focally the characteristic reticular growth pattern of yolk sac tumors, with the presence of Schiller-Duval bodies and intra- and extracellular hyaline globules. Immunohistochemical studies performed in one case showed positive staining for keratin and alpha-fetoprotein in both the spindle cell and reticular components of the tumor. Follow-up information was obtained in two patients; they both died of tumor with metastases to the lungs 1 year after initial diagnosis. The present cases expand the spectrum of histopathologic growth patterns that may be observed in yolk sac tumors of the mediastinum and stress the issue of careful sampling and evaluation of mediastinal neoplasms for arriving at the correct diagnosis.

Primary mediastinal choriocarcinomas: a clinicopathologic and immunohistochemical study of eight cases

Primary choriocarcinoma of the anterior mediastinum is by far the rarest and most controversial form of extragonadal germ cell tumor. A clinicopathologic study of eight primary mediastinal neoplasms bearing the histopathologic and immunohistochemical features of choriocarcinoma is presented. The patients were all men between the ages of 21 and 63 years (mean, 42 years). Clinical symptoms included shortness of breath, chest pain, cough, and superior vena cava syndrome; one patient also had gynecomastia. All patients presented with large anterior mediastinal masses on chest radiographs that measured an average of 10 cm in greatest diameter. Grossly, the tumors were described as large, soft, extensively hemorrhagic, and with foci of necrosis. Histologically, they were characterized by a dual cell population composed of cytotrophoblastic cells with uniform, round nuclei, clear cytoplasm, and prominent nucleoli admixed with large, multinucleated syncytiotrophoblastic cells with bizarre nuclei, prominent nucleoli, and abundant eosinophilic cytoplasm. Immunohistochemically, the tumors were notable for strong keratin and beta-human chorionic gonadotropin (HCG) positivity. Seven patients presented at the time of diagnosis with thoracic and extrathoracic (liver, adrenal, kidney, and spleen) metastases. In one case, the tumor was entirely confined to the mediastinum. All patients died over a period of 1 to 2 months. Complete autopsies were performed in all cases; none of the patients showed evidence of a testicular tumor or scar after thorough examination of the testes on serial sectioning. The present cases demonstrate the widespread distribution of germ cells in the human body and lend further support to the existence of primary extragonadal choriocarcinoma arising in the thymic region.

Primary germ cell tumors of the mediastinum: I. Analysis of 322 cases with special emphasis on teratomatous lesions and a proposal for histopathologic classification and clinical staging

BACKGROUND

Primary germ cell tumors of the mediastinum are unusual neoplasms with histopathologic features that are similar to those of germ cell tumors in the gonads. However, their clinical features, behavior, and spectrum of pathologic features in the mediastinum have not yet been fully defined.

METHODS

The clinical and pathologic features of 322 cases of primary mediastinal germ cell tumors were reviewed, with special emphasis on teratomatous lesions. The tumors were divided into groups according to their histologic features and correlated with their order of frequency, patient gender and age distribution, and morphologic features. A clinical staging scheme based on the extent and location of the lesions was devised.

RESULTS

The overwhelming majority of patients were men (320); only 2 were women (both had teratomatous lesions with additional malignant components). The patients' ages ranged from 1 to 79 years (mean, 40 years). Histologically, all types of germ cell tumors were represented, including 138 teratomas (87 mature teratomas, 6 immature teratomas, and 45 teratomas with additional malignant components); 120 seminomas; 52 nonseminomatous, nonteratomatous germ cell tumors (38 yolk sac tumors, 6 embryonal carcinomas, and 8 choriocarcinomas); and 12 combined germ cell tumors without teratomatous components. The teratomatous lesions with additional malignant components were further separated into subtypes based on the histologic types of their malignant components, i.e., epithelial, mesenchymal, etc. Clinical staging was possible in 242 cases, with 191 cases (79%) in Stage I, 4 cases (1.6%) in Stage II, and 47 cases (19.4%) in Stage III. In each group, the clinical staging correlated well with the clinical outcome for the majority of patients.

CONCLUSIONS

The results of this study showed that mediastinal germ cell tumors have demographic and histopathologic distributions similar to those of tumors occurring in the male gonads, with teratomatous and seminomatous lesions being the most common. Among the nonseminomatous germ cell tumors in this study, the yolk sac tumors appeared to occur the most frequently (the ratio of yolk sac tumor occurrence to embryonal carcinoma occurrence was 6.1:1). In addition, the subclassification of teratomas with additional malignant components based on the histologic types of malignancies may lead to more therapy choices for patients. At the same time, the use of a clinical staging scheme may be of value in predicting clinical outcome and planning therapy.

Primary germ cell tumors of the mediastinum: III. Yolk sac tumor, embryonal carcinoma, choriocarcinoma, and combined nonteratomatous germ cell tumors of the mediastinum--a clinicopathologic and immunohistochemical study of 64 cases

BACKGROUND

Yolk sac tumor (YST), embryonal carcinoma (EC), choriocarcinoma (CC), and combined germ cell tumors (CGCTs) of the mediastinum are uncommon neoplasms. Only sporadic cases have been documented in the literature; therefore, the clinical behavior of these tumors when located in the mediastinum remains relatively unknown.

METHODS

The clinical and pathologic features of 64 cases of primary YST, EC, CC, and CGCTs without teratomatous components were reviewed. The immunohistochemical findings in 29 cases were also analyzed using a panel of monoclonal and polyclonal antibodies in formalin fixed, paraffin embedded tissues.

RESULTS

The patients were all men between the ages of 14 and 63 years (mean, 38.5 years). Their clinical symptoms included chest pain, shortness of breath, chills, fever, and superior vena cava syndrome. None of the patients had a previous history of testicular neoplasm or tumor elsewhere. Macroscopically, the lesions in 27 patients were described as large, soft, hemorrhagic, and in some cases necrotic, and varied in greatest dimension from 6 to 20 cm. Histologically, the tumors displayed morphologic features similar to those of their gonadal counterparts. Pure YSTs accounted for the majority of cases in this series (38 of 64, 60%), followed by pure CCs (8 of 64, 12%) and pure ECs (6 of 64, 9%). CGCTs accounted for only 18% of the total cases (12 of 64). YSTs showed a variety of growth patterns; however, the reticular pattern was the most commonly observed. ECs showed a more solid growth pattern with marked pleomorphism of the tumor cells and abundant areas of necrosis. CCs were characterized by the presence of cytotrophoblastic and syncytiotrophoblastic elements with frequent areas of necrosis and hemorrhage. The cases of nonteratomatous CGCT consisted of 5 cases of EC + YST, 2 cases of EC + seminoma, 4 cases of YST + seminoma, and 1 case of EC + CC. In clinical staging, 14 patients were Stage I, 6 were Stage II, and 19 were Stage III. Information on follow-up ranging from 1 month to 13 years was available for 40 patients. Seventeen patients with YST died of their tumors. Of these, 10 who presented with Stage III disease died within the first 2 years. Unfortunately, no clinical staging was obtained for the other 7 patients in this group, and they died within 6-36 months. It is noteworthy that 4 patients with YST have survived for more than 2 years; these patients presented in Stages I and II, and 2 of them received aggressive therapy with chemotherapeutic agents and radiation. Two patients with Stage III EC died within 2 years. The remaining 4 patients with EC were lost to follow-up. Eight patients with CC died within 6 months after initial diagnosis; 7 of them presented Stage III disease and only 1 presented with Stage I. In the nonteratomatous CGCT category, 2 patients with EC + YST died within 2 years after initial diagnosis, whereas 3 patients with YST + seminoma were alive after 4-9 years.

CONCLUSIONS

The results of this study confirm the aggressive nature of primary nonseminomatous germ cell tumor of the mediastinum; 72% of the patients with adequate follow-up died of their tumors within 6-36 months after diagnosis, despite aggressive therapy. Clinical and pathologic staging of mediastinal YST, EC, and CGCT are important parameters that may be helpful in predicting the clinical outcomes of patients with these tumors. The authors' findings suggest that the majority of tumors that are not limited to the mediastinum at the time of diagnosis have more aggressive behavior. On the other hand, mediastinal choriocarcinomas appeared to follow a very aggressive clinical course, regardless of treatment modality or clinical tumor stage.

Primary germ cell tumors of the mediastinum: II. Mediastinal seminomas--a clinicopathologic and immunohistochemical study of 120 cases

BACKGROUND

Primary seminomas of the mediastinum are unusual neoplasms that are morphologically indistinguishable from their gonadal counterparts but may have different biologic behavior because they arise at this particular location.

METHODS

The clinical and pathologic features in 120 cases of primary mediastinal seminoma were reviewed, and the immunohistochemical staining patterns in 50 of these tumors were also analyzed.

RESULTS

The patients were all men between the ages of 14 and 79 years (mean age, 46.5 years). Their clinical symptoms included cough, chest pain, and dyspnea. In some patients, the lesions were asymptomatic and discovered incidentally on routine chest radiographs. None of the patients had a previous history of testicular neoplasm or tumor elsewhere. Macroscopically, the tumors were described as soft and tan, with a slightly lobulated cut surface, and measured up to 16 cm in greatest dimension. Histologically, the morphologic features were similar to those of tumors occurring in the gonads, namely, a neoplastic proliferation of round-to-polygonal cells with indistinct cell borders, clear-to-lightly-eosinophilic cytoplasm with round-to-oval nuclei and prominent nucleoli, associated with a prominent inflammatory background composed mainly of mature lymphocytes. Necrosis, hemorrhage, multinucleated giant cells, granulomatous reaction, and remnants of thymic tissue were observed in a variable number of cases; mitoses were rare. Immunohistochemical studies in 50 cases showed cytoplasmic staining with placental alkaline phosphatase in 80% of the tumors, focal dotlike positivity for CAM 5.2 low-molecular-weight keratins in 75%, focal cytoplasmic staining for wide-spectrum keratin in 70%, focal positive reaction with vimentin in 70%, and focal positivity with HCG in singly scattered cells in 5%. Immunostains for carcinoembryonic antigen, epithelial membrane antigen, and alpha-fetoprotein were negative in all the cases studied. Fifty patients were Stage I, 3 patients were Stage II, and 12 patients were Stage III. Clinical follow-up information was obtained for 65 cases (54%). Forty-nine patients were alive and disease free after a period ranging from 1 to 19 years (mean follow-up, 10 years). Sixteen patients died within the same period and were found to have metastases to distant organs. Of the 16 patients who died, 6 showed extension of the tumor outside of the mediastinal compartment at the time of initial diagnosis (Stage III lesions). Aside from clinical staging, the authors' findings also suggest that patients >37 years have worse outcomes than younger individuals. The authors were unable to find any correlation between histopathologic features and clinical behavior in any of these cases.

CONCLUSIONS

Clinical and pathologic staging of mediastinal seminomas are important parameters that can be useful in determining the clinical outcomes of patients with these tumors. Tumor invasion into adjacent organs represents a marker of increased morbidity and mortality. The authors' findings suggest that patients with mediastinal seminomas may have a very good prognosis when the diagnosis is made early; patients with more advanced lesions may require more aggressive therapy for improved local control and prevention of distant metastases.

Mediastinal yolk sac tumors associated with prominent multilocular cystic changes of thymic epithelium: a clinicopathologic and immunohistochemical study of five cases

Five cases of yolk sac tumor of the anterior mediastinum associated with prominent thymic cystic changes are presented. The patients were five men between the ages of 17 and 22 years (mean, 19.5 yr). Clinically, four patients presented with symptoms of chest pain and shortness of breath, whereas the fifth was asymptomatic: his tumor was discovered during a routine physical examination. None of the patients had a history of previous tumor elsewhere. Grossly, the tumors were described as cystic lesions measuring between 8 and 12 cm in greatest dimension. Histologically, the tumors showed prominent cystic changes reminiscent of those observed in acquired multilocular thymic cysts, i.e., the presence of cystic cavities lined by squamous epithelium with prominent inflammatory changes, lymphoid hyperplasia, cholesterol cleft granulomas, and remnants of thymic tissue in the walls of the cysts. In addition, there was a neoplastic cellular proliferation composed of small cells with scant cytoplasm, round nuclei, and inconspicuous nucleoli adopting a reticular pattern of growth and, in some areas, embedded in abundant myxoid stroma. Numerous intra- and extracellular hyaline globules, as well as Schiller-Duval bodies, could also be identified. Immunohistochemical studies showed positive reaction with alpha-fetoprotein antibodies in the tumor cells. Follow-up information obtained in these patients showed that all had died of tumor 1 to 3 years after initial diagnosis. The present cases document another unusual but distinctive growth pattern of yolk sac tumor in the mediastinum and highlight the importance of proper sampling of cystic lesions in this location.

Malignant cartilaginous tumors of the mediastinum: clinicopathological study of six cases presenting as extraskeletal soft tissue masses

Cartilage and bone-forming tumors of the mediastinum are extremely rare neoplasms with very few cases having been reported in the literature. We studied six cases of primary malignant cartilaginous tumors presenting as extraskeletal soft tissue masses in the posterior mediastinum. The patients were five women and one man aged 11 to 63 years (median, 31 years). Histologically, the lesions showed a spectrum of features that ranged from mesenchymal chondrosarcoma, to extraskeletal myxoid chondrosarcoma, to moderately well to poorly differentiated chondrosarcoma. In all cases, the lesions presented as well-circumscribed tumor masses centered in the soft tissues in the posterior mediastinum without radiographic evidence of origin from bone. Because of their relatively small size, good circumscription, focal areas of calcification, and posterior mediastinal location, the preoperative clinical diagnoses included benign neurogenic tumor and neuroblastoma. All of the lesions were treated by complete surgical excision, followed in two cases by postoperative radiation therapy. Clinical follow-up was available in five cases: two patients with mesenchymal chondrosarcoma presented with local recurrence after 3 and 7 years, one developed metastases to the sacrum 8 years after initial diagnosis and died, and one was alive and well without evidence of disease after 6 years. The patient with myxoid chondrosarcoma of the posterior mediastinum developed bilateral pulmonary metastases 10 months after surgery and has been lost to follow-up since. Our findings reinforce previous observations on the occurrence of extraskeletal cartilaginous tumors in the mediastinum and indicate that these tumors can show a propensity for local aggressive behavior with high recurrence rate and a definite potential for distant metastases. Such tumors should be considered in the differential diagnosis of malignant neoplasms presenting as a soft tissue mass in the posterior mediastinum.

Squamoid eccrine ductal carcinoma

We describe three cases of a distinctive cutaneous adnexal neoplasm showing features of eccrine ductal differentiation that were characterized by a prominent squamoid component. The tumours presented as solitary dermal nodules on the head and neck areas and the extremities in elderly patients. Histologically, they were characterized by a prominent squamous proliferation with atypia, keratinous cyst formation and squamous eddies which seemed to merge with areas showing eccrine ductal differentiation, including ductular formations in continuity with eccrine ductal epithelium. Clinical follow-up in one case showed multiple local recurrences over a period of 3 years despite complete surgical excision. Squamoid eccrine ductal carcinoma should be considered in the differential diagnosis of cutaneous adnexal neoplasms showing squamoid and ductal features of differentiation.

Inflammatory pseudotumor of lymph nodes: a study of 25 cases with emphasis on morphological heterogeneity

The clinicopathological and immunohistochemical findings in 25 cases of inflammatory pseudotumor of lymph nodes (IPT) are presented. The patients were 13 women and 12 men between 8 and 81 years of age. Clinically, symptoms of prior infection, fatigue, abdominal pain, weight loss, fever of unknown origin, pelvic inflammatory disease, or nausea and night sweats were obtained in 15 patients, whereas six patients presented with asymptomatic lymphadenopathy. In four additional patients, no clinical information was obtained. The involved nodes included cervical, supraclavicular, inguinal, mesenteric, and mediastinal lymph nodes. In two cases, there was synchronous involvement of separate lymph node groups (inguinal and cervical in one case and cervical and mediastinal in another case), whereas in a third patient there was synchronous involvement of the spleen and a paraaortic lymph node. Histologically, the lesions were characterized by a fibrosing/inflammatory process that showed marked heterogeneity and striking variation from case to case. Based on their histological features, the lesions could be classified into three different groups: Stage I was characterized by the appearance of single or multiple small foci containing a spindle cell proliferation admixed with a prominent inflammatory background, with complete preservation of the remainder of the nodal architecture; stage II was characterized by more diffuse involvement of the lymph node with a marked inflammatory response admixed with a prominent myofibroblastic proliferation leading to subtotal effacement of the nodal architecture, often with extension of the process beyond the capsule into perinodal fat; and stage III was characterized by almost complete replacement of the lymph node by diffuse sclerosis with scant residual inflammatory elements and total loss of the normal nodal architecture. Immunohistochemical studies in 20 cases showed a striking number of vimentin- and actin-positive myofibroblastic cells with moderate increase in CD20/CD45+ small lymphocytes and polyclonal plasma cells in the stage I lesions, the emergence of numerous CD68+ histiocytes admixed with lymphocytes, plasma cells, and abundant fibromyofibroblastic cells in the stage II lesions, and only few remaining scattered CD68+ histiocytes and fibroblasts in the stage III lesions. Our findings suggest that inflammatory pseudotumor of lymph node represents an evolving, dynamic process that may adopt different morphological appearances depending on its stage of evolution. Recognition of the various stages of this process may be of importance for differential diagnosis with other fibrosing/inflammatory conditions of lymph nodes.

Cytokeratin 20 immunoreactivity distinguishes Merkel cell (primary cutaneous neuroendocrine) carcinomas and salivary gland small cell carcinomas from small cell carcinomas of various sites

Cytokeratin 20 (CK20) is a low-molecular-weight cytokeratin (CK) that shows restricted expression in the gastrointestinal epithelium, urothelium, and Merkel cell. Recent studies have suggested that since Merkel cell (primary cutaneous neuroendocrine) carcinomas are consistently CK20-positive, this feature may help to distinguish it from pulmonary small cell carcinomas. However, only limited numbers of these tumors have been studied, and the pattern of CK20 expression in other small cell carcinomas has not been established. Therefore, we studied CK20 expression in small cell carcinomas from a wide variety of sites. Immunohistochemical study was performed on paraffin sections using CK20 antibody, coupled with antigen retrieval by pressure cooking in citrate buffer. The cases included 34 Merkel cell carcinomas and 89 small cell carcinomas from various sites (pulmonary, 37; gastrointestinal tract, nine; pharynx and tongue, two; sinonasal tract, three; salivary gland, five; larynx, nine; breast, two; thymus, three; uterine cervix and corpus, 12, prostate, three; urinary bladder, two; kidney, one; pancreas, one). In addition, all cases were immunostained with pan-CK (MNF-116) and low-molecular-weight CK (CAM5.2) antibodies to ascertain their epithelial nature. With the exception of one case, all Merkel cell carcinomas were CK20-positive; and 30 of the 33 cases showed a punctate pattern. Almost 100% of tumor cells were positive, except for two cases that showed staining of 10% and 30% of tumor cells, respectively. Among the other small cell carcinomas, only five cases were CK20-positive, including one of 37 pulmonary (40% cells positive in punctate pattern), one of 11 cervical (10% cells positive), and three of five salivary gland (100% cells positive). We conclude that CK20-positivity in a small cell carcinoma of uncertain origin strongly predicts a diagnosis of Merkel cell carcinoma, especially if the majority of tumor cells are positive. A negative CK20 reaction can practically rule out Merkel cell carcinoma, provided that an effective antigen retrieval technique is used and appropriate staining is obtained with other cytokeratin antibodies. The frequent CK20 positivity observed in salivary gland small cell carcinomas in this series suggests that at least some of them may be more closely related biologically to Merkel cell carcinoma than to pulmonary-type small cell carcinoma. This may explain why they are far less clinically aggressive than other small cell carcinomas.

Primary malignant 'triton' tumour of the lung

Two cases of malignant 'triton' tumour arising within lung parenchyma are described. The patients were a three-year-old child and a 53-year-old man. Both patients presented with shortness of breath and a large intrapulmonary mass on chest X-ray. Neither patient had a history of von Recklinhausen's neurofibromatosis. The lesions were treated by pneumonectomy. Grossly, both tumours presented as large, soft and gelatinous intraparenchymatous masses measuring 130 mm and 80 mm, respectively. Histologically, they were characterized by an atypical spindle cell proliferation embedded in an abundant myxoid stroma. Focal areas of rhabdomyoblastic differentiation characterized by large cells with abundant eosinophilic cytoplasm and occasional cytoplasmic cross-striations could be seen admixed with the atypical spindle cell elements. Immunohistochemical studies showed a focal positive reaction for S-100 protein in the atypical spindle cells embedded within the myxoid stroma, and a strong positive reaction for desmin and myoglobin in the rhabdomyoblastic areas. The child died three months after diagnosis with extension of the tumour into the thoracic cavity. The second patient has been lost to follow-up. Although rare, malignant 'triton' tumour should be considered in the differential diagnosis of primary spindle cell sarcomas of the lung.

Primary leiomyosarcomas of the lung: a clinicopathologic and immunohistochemical study of 18 cases

We studied 18 patients with primary malignant smooth muscle tumors of the lung (7 women and 11 men, 5-76 yr old, with a mean age of 50 yr). Lesions varied from 1.7 to 10 cm in greatest diameter. The tumors were classified as low (4 cases), intermediate (2), or high grade (12). Low-grade lesions were characterized by an orderly proliferation of fascicles of spindle cells that intersected at right angles and showed oval-to-spindle cells with cigar-shaped nuclei, minimal pleomorphism, and low mitotic activity, without hemorrhage or necrosis. Intermediate-grade lesions retained the fascicular configuration but showed increased cellularity with atypia and dense chromatin pattern, occasional pleomorphism, and mild increase in mitotic activity. High-grade lesions showed high cellularity, marked pleomorphism and atypia, frequent areas of hemorrhage and necrosis, and high mitotic activity. Immunohistochemical studies in 16 cases showed positive staining of tumor cells with smooth muscle actin in 12, desmin in 5, and coexpression of actin and/or desmin and keratin in 3. Six patients with low- and intermediate-grade lesions were alive and well from 2 to 12 years after diagnosis (mean follow-up time, 6 yr); 8 with high-grade lesions died of their tumors with widespread metastases from 1 to 24 months after diagnosis (median survival time, 5 mo). One patient whose tumor showed features of high-grade leiomyosarcoma was alive and well 12 years after surgery. Three patients with high-grade tumors were lost to follow-up. Our findings suggest that histologic grade may be the most reliable prognostic parameter for predicting clinical behavior in primary leiomyosarcoma of the lung and that smooth muscle actin is the most sensitive immunohistochemical marker for establishing the diagnosis in these tumors. Primary leiomyosarcoma should be considered in the differential diagnosis of pulmonary spindle cell neoplasms; histologic grading may be of value in the planning of therapy and assessment of prognosis for these lesions.