Tumoral, quasitumoral and pseudotumoral lesions of the superficial and somatic soft tissue: new entities and new variants of old entities recorded during the last 25 years. Part XII: appendix

In an eleven part series published in Pathologica, we have presented various tumoral, quasitumoral and pseudotumoral lesions of the superficial and somatic soft tissue (ST), which emerged as new entities or as variants of established entities during the last quarter of a century. Detailed clinicomorphological and differential diagnostic features of approximately sixty entities were chosen on the basis of their clinical significance and morphologic distinctiveness. The series included fibrous and myofibroblastic tumors (e.g. solitary fibrous tumor, high grade classic and pigmented dermatofibrosarcoma protuberans, inflammatory myofibroblastic tumor and myofibrosarcomas), fibromyxoid and fibrohistiocytic neoplasms (e.g., Evans' tumor, phosphaturic mesenchymal tumor, inflammatory myxohyaline tumor), special adipocytic/vascular/and smooth muscle lesions (e.g., chondroid lipoma, Dabska's tumor, ST hemangioblastoma, lipoleiomyosarcoma), epithelioid mesenchymal malignancies of diverse lineages (e.g., epithelioid liposarcoma, proximal-type epithelioid sarcoma, neuroendocrine extraskeletal chondromyxoid sarcoma), ST Ewing's tumor and peripheral nerve sheath tumors (perineuriomas and pigmented and rosetting tumors of the schwannoma/neurofibroma group), extranodal dendritic or histiocytic proliferative processes (follicular dendritic cell sarcoma, Rosai-Dorfman disease, Castleman's disease, and plexiform xanthomatous tumor), and tumors with myoepithelial differentiation. The section devoted to selected pseudotumoral entities considered representatives of the hamartoma group (neural fibrolipomatous hamartoma, ectopic hamartomatous thymoma, rudimentary meningocele), metabolic diseases (amyloid tumor, nephrogenic fibrosing dermopathy, tophaceous pseudogout, pseudoinfiltrative parathyromatosis), stromal tissue reactions to trauma (fibroosseous pseudotumors of digits) and infections (bacillary angiomatosis), and normal organs (glomus coccygeum). To conclude the descriptive phase, supplementary material has now been collected and appended in an attempt to provide a quick digest of essential knowledge both for comparison and differential diagnosis. The data have been tailored to synthesize diverse sources, integrating clinical elements and references to articles that previously appeared in Part I ("Introduction"), Part II ("The List and Review of New Entities") and Parts III to XI ("Excerpta"). At the very least we hope this final part ("Appendix") will provide the reader with a useful tabular organization of ST lesions and a reference resource.

Expression of CD30 (Ber-H2) in nasopharyngeal carcinoma, undifferentiated type and lymphoepithelioma-like carcinoma. A comparison study with anaplastic large cell lymphoma

AIMS

Undifferentiated nasopharyngeal non-keratinizing carcinoma (UNPC), formerly known as lymphoepithelioma, frequently metastasizes at an early stage to regional lymph nodes and, thus, may be difficult to distinguish from Hodgkin's lymphoma (HL) or anaplastic large cell lymphoma (ALCL). CD30 expression is a useful diagnostic stain in both HL and ALCL, but its expression in UNPC deserves clarification. The aim of this study was to evaluate CD30 expression in UNPC and lymphoepithelioma-like carcinoma (LELC) from other anatomic locations and compare it with ALCL and squamous cell carcinoma (SCC).

METHODS AND RESULTS

CD30 immunoreactivity was examined in 38 cases of primary or metastatic UNPC, six cases of LELC, 10 cases of SCC and seven cases of ALCL. CD30 immunoreactivity was observed in four of 38 (10.5%) cases of UNPC. CD30 staining was absent in all cases of LELC (0/6) and SCC (0/10). All cases of ALCL (7/7) were strongly positive for CD30.

CONCLUSIONS

The majority of cases of UNPC are immunohistochemically negative for CD30; however, a small subset of cases expresses CD30 antigen. These findings provide additional evidence that CD30 expression is not restricted to neoplasms of lymphoid origin. This should be taken into consideration when interpreting CD30 immunohistology and the possibility of UNPC.

Diagnosis of thymoma

The diagnosis of thymic epithelial neoplasm has been a topic of controversy for many years. Reasons for this include the lack of predictive value associated with the morphology of these tumours and the multiplicity of classification schemes and terminologies proposed over the years. Recently, a new classification schema was introduced by the World Health Organization (WHO) in an attempt to standardise nomenclature and facilitate the diagnosis of primary thymic epithelial neoplasms. This schema, although not originally intended as a new histological classification, but rather as a means for translating equivalent terms from the various existing classifications, has represented a major step forward in this direction. However, problems still exist with the WHO schema, particularly with some of the criteria for the various histological subtypes as well as with issues of interobserver reproducibility. For this reason, we favour using a much more simplified approach to the morphological classification of thymic epithelial neoplasms. A personal approach to the morphological diagnosis of thymoma is described, with a brief explanation for the rationale for simplifying the existing diagnostic categories.

Chromophobe renal cell carcinoma with microcystic and adenomatous arrangement and pigmentation—a diagnostic pitfall. Morphological, immunohistochemical, ultrastructural and molecular genetic report of 20 cases

We present clinical, morphological, immunohistochemical, ultrastructural and molecular genetic features of 20 cases of a peculiar form of chromophobe renal cell carcinoma (CRCC) with morphology differing from that of conventional CRCC. Microscopically, the typical features of the tumors were microcystic arrangement and formation of adenomatous structures. Microcystic areas were composed of smaller eosinophilic and bigger pale cells having cytological appearance typical of conventional CRCC. Cytological features of the adenomatous structures were mostly different from those of conventional CRCC. They had a typical columnar arrangement with nuclei positioned at the base of the glandular structures and a small amount of a deeply eosinophilic cytoplasm often endowed with brush border facing the lumen of the glands. In addition, all the tumors showed a brown pigmentation. The pigmentation was located mostly extracellularly, where it formed pools of heavy deposits. Microscopic calcifications present in all cases formed psammoma bodies or else the calcifications were more extensive and amorphous in shape. Ultrastructurally, the cells showed features characteristic of CRCC: typical cytoplasmic vesicles were 100-700 nm in size and mitochondria had tubulovesicular, lamellar or circular cristae. Some tumor cells contained dark, variously sized electron-dense pigment granules. Neither melanosomes nor membrane-bound neurosecretory granules were seen. Using fluorescence in-situ hybridization probes for chromosomes 1, 2, 6, 10, 13, 17 and 21, the tumors revealed massive loss of tested chromosomes typical for conventional CRCC. Monosomy of chromosomes 1, 2, 6, 10, 13 and 21 was found in 100, 36, 91, 82, 82, 82 and 64% of cases, respectively. None of the cases showed mutation of exons 9, 11, 13 and 17 of the c-kit gene. The important feature of pigmented microcystic chromophobe renal cell carcinoma is a relatively benign biological behavior and the absence of distant metastases and sarcomatoid transformation.

Carcinomas arising in multilocular thymic cysts of the neck: a clinicopathological study of three cases

AIMS

To report three cases of primary carcinoma of the neck arising in multilocular thymic cysts (MTC).

METHODS AND RESULTS

The patients were three men aged 47, 50 and 52 years who presented with a painless neck mass of several weeks' duration. The patients had no history of previous surgical procedures or of malignancy elsewhere. The tumours in all three patients were located on the right lateral side of the neck; all patients underwent complete surgical resection of the mass. Grossly, the tumours were cystic and measured between 20 and 30 mm in greatest diameter. Histologically, the tumours showed cyst walls lined by squamous epithelium. The cyst walls contained prominent germinal centres with lymphoid hyperplasia, cholesterol cleft granulomas, and scattered keratinized structures reminiscent of Hassall's corpuscles. In addition, a neoplastic cellular proliferation composed of round to oval cells arranged in sheets and originating from the lining of the cystic structures was present. The neoplastic cells showed moderate amounts of eosinophilic cytoplasm, round nuclei, and, in some areas, prominent nucleoli. Mitotic figures were easily found, and cellular pleomorphism was present in several areas. In two cases the tumours showed features of basaloid carcinoma of the thymus, while in one case the pattern was that of squamous cell carcinoma. Immunohistochemical studies for keratin showed a strong positive reaction in the tumour cells, while leucocyte common antigen strongly stained the lymphoid background. Follow-up information obtained in two patients showed them to be alive 6 months after initial diagnosis. One patient was lost to follow-up.

CONCLUSION

The cases described here represent an unusual variant of carcinoma arising in multilocular thymic cyst in the neck region.

[Spindle cell and cuboidal renal cell carcinoma (loopoma). 10 case reports]

BACKGROUND

Current classification systems of neoplasms arising from renal parenchyma distinguish 5 categories of renal cell carcinoma (RCC), i.e. conventional RCC, papillary RCC, chromophobe RCC, collecting duct/medullary RCC and unclassified RCC. We present 13 cases of unusual and unclassified spindle and cuboidal renal cell carcinomas.

METHODS AND RESULTS

The studied group consisted of 13 patients (7 men and 6 women). They ranged in age from 22 to 65 years (mean 57.3). Generally, the tumours were well circumscribed and confined to the kidney, whitish to grey on section with a diameter 4.5-13 cm (mean 8.6 cm). One patient was investigated for loin pain and nocturia. Three patients had staghorn nephrolithiasis and vague sonographic findings in renal parenchyma. In one patient the renal tumour was found when examined on follow-up examination for prostatic adenocarcinoma. None of our patients was known to have elevated levels of parathyroid hormone due to hyperplasia, adenoma or carcinoma of the parathyroid gland. Clinical follow-up of the patients ranged from 9 months to 8 years (mean 2.3 years). Microscopically, the tumours were composed of two main populations of cells: flattened, spindle cells with sparse cytoplasm and small cuboidal cells with clear to light eosinophilic cytoplasm. Eight patients are currently well without signs of recurrence or metastasis, one had metastasis in the regional lymph node at the time of nephrectomy, one died of unrelated cause, and three were lost to follow-up.

CONCLUSIONS

We present 13 cases of unclassified RCC. Our cases were histologically, immunohistochemically and ultrastructurally similar to the hitherto reported case reports of this variant of RCC. It is obvious, that that variant of RCC should be recognised as a new subtype of RCC.

Spindle and cuboidal renal cell carcinoma, a tumour having frequent association with nephrolithiasis: report of 11 cases including a case with hybrid conventional renal cell carcinoma/ spindle and cuboidal renal cell carcinoma components

AIMS

We present the largest series of an unclassified subtype of renal cell carcinoma, which seems to be a distinct morphological entity and which is sometimes designated as spindle and cuboidal renal cell carcinoma.

METHODS AND RESULTS

Eleven cases of spindle and cuboidal renal cell carcinoma were found among 7000 primary renal cell tumours in Pilsen's routine and consultation files. The patients were five men and six women. They ranged in age from 22 to 65 years (mean 56.8). Microscopically, the tumours were composed of two main populations of cells. First, the preponderant type of cells was formed by flattened, spindle cells with sparse cytoplasm. The second cell type was a small cuboidal cell with clear to light eosinophilic cytoplasm. Spindle-shaped cells were arranged in a fascicular pattern often reminiscent of low-grade smooth muscle tumours. Solid areas of spindle cells were also present. Small cuboidal cells formed sparse tubular structures lined by a row of single cells. In addition to all previous published cases of spindle and cuboidal renal cell carcinoma we observed an association of nephrolithiasis in our cases. It was seen in 3/11 of our patients. A previously unreported feature is the occurrence of a conventional renal cell carcinoma component in one of our cases. Seven of our patients are currently well without signs of recurrence or metastasis, one had metastasis in a regional lymph node at the time of nephrectomy, one died of an unrelated condition, and two were lost to follow-up.

CONCLUSIONS

We present 11 cases of spindle and cuboidal renal cell carcinoma, which is believed to be a distinctive morphological entity. Our cases were histologically, immunohistochemically and ultrastructurally similar to the previously reported cases of spindle and cuboidal renal cell carcinoma. In contrast to all previously reported cases of spindle and cuboidal renal cell carcinoma, we observed an association with nephrolithiasis in three of our cases; moreover, one of our tumours had a conventional renal cell carcinoma component and another revealed a metastatic focus in a regional lymph node. None of our patients died of the disease. This study confirms that spindle and cuboidal renal cell carcinoma has a low malignant potential.

[Metanephric adenoma. 11 case reports and detection of collagen spherules in one tumor]

Eleven cases of metanephric adenoma are reported. The tumors were selected out of 6500 tumorous and pseudotumorous lesions of the kidney in our registry. Female to male ratio was 1:1.2. The average age of the patients was 48.3 years, with a range of 13-79 years. The mean size of the tumors was 7.2 cm. The tumors were spherical in shape, whitish to yellowish in colour. Histologically, they were arranged in a mainly tubular pattern with short pseudopapillae. The tumorous cells were deeply eosinophilic to basophilic with predominantly round nuclei. Psammomatous bodies were numerous. Immunohistochemically, they reacted positively with antibodies against cytokeratins, vimentin, and WT1. Ultrastructurally, the cytoplasm contained mitochondria, RER, and ribosomes. A collagenous spherulosis, identical with those in salivary gland and mammary tumors, was revealed in one case. The spherules were located mainly inside tubular structures. Ultrastructurally, they were composed of basement membrane-like material, which was surrounded by epithelial cells. Follow-up all of our patients was negative (if known) for 10 months to 4 years.

Primary signet ring cell adenocarcinomas of the lung: a clinicopathological study of 15 cases

AIMS

We describe the clinicopathological characteristics of 15 cases of primary signet ring cell adenocarcinoma of the lung and highlight the importance of recognizing that not all adenocarcinomas with signet ring cell features represent metastatic adenocarcinomas.

METHODS AND RESULTS

We evaluated the clinicopathological and immunohistochemical features of 15 cases of signet ring cell adenocarcinoma of the lung. The patients were 12 men and three women, age 30-75 years (mean 52.5 years). No evidence of a primary tumour elsewhere could be found on thorough clinical examination. Nine patients underwent resection and the remainder were biopsied. The tumours ranged from 18 to 80 mm in greatest dimension. Microscopically, two distinct patterns of growth were recognized: acinar and diffuse. The tumours were characterized by the presence of >75% signet ring cells. Periodic acid-Schiff and mucicarmine showed strong intracellular positive staining. Immunohistochemical stains for TTF-1 (6/6) and CEA (9/9) showed strong positive reaction in all cases evaluated. Three out of six cases were also positive for cytokeratin 7. All the tumours (6/6) were negative for cytokeratin 20, ER, PR and GCDFP-15. Follow-up information was obtained in 11 patients; six patients died within 1 year and five patients were alive from 3 to 36 months after initial diagnosis.

CONCLUSION

These cases highlight an unusual histological growth pattern of primary lung adenocarcinoma that may be mistaken for a metastasis from an occult primary. The recognition of this pattern of lung tumours is important for proper treatment.

Thymoma with prominent cystic and hemorrhagic changes and areas of necrosis and infarction: a clinicopathologic study of 25 cases

Twenty-five cases of thymoma with prominent cystic and hemorrhagic changes and areas of necrosis and infarction are presented. The patients were 11 women and 14 men between the ages of 18 and 73 years (median 45.5 years). Clinically, nine patients were asymptomatic and their mediastinal tumor was discovered on routine chest radiograph. Sixteen patients presented with symptoms of chest pain and cough. All patients underwent surgical resection of their tumor. Grossly, the tumors were described as well circumscribed and encapsulated, with the exception of two that showed infiltration of pleura and pericardium. The tumors measured from 4 to 13 cm in greatest dimension. On cut surface they showed prominent cystic areas and foci of hemorrhage and necrosis. Histologically, the tumors contained solid areas showing an admixture of round to oval epithelial cells devoid of atypia admixed with small lymphocytes in varying proportions. Cystic changes with areas of necrosis, infarction, and hemorrhage were present in all cases and comprised extensive areas of the tumors. The areas of infarction showed features of ischemic necrosis and were always intimately associated with vaso-occlusive and thrombotic phenomena and with cystic and hyperplastic changes of adjacent thymic epithelium. Clinical follow-up in 14 patients showed that 11 were alive and well from 1 to 18 years after surgery (median follow-up 9 years). Three patients died: one of complications during the immediate postoperative period, one because of colonic adenocarcinoma 9 years after diagnosis of the mediastinal tumor, and one because of pneumonia 6 years later. The two patients with invasive tumors were lost to follow-up. The present study appears to indicate that areas of hemorrhage and necrosis in well encapsulated, noninvasive thymomas do not portend an adverse prognosis.

Immunohistochemical differential diagnosis of pleural effusions, with emphasis on malignant mesothelioma

The immunohistochemical diagnosis of atypical epithelial proliferations in pleural fluid is a challenging topic in cytopathology and surgical pathology. Mesothelioma may be simulated clinically and radiologically by several other nonneoplastic and neoplastic disorders, mandating that strict histologic, histochemical, immunohistochemical, and ultrastructural guidelines be followed for its diagnosis. Because of its availability to most laboratories, immunohistochemistry has emerged as the most commonly used procedure for the diagnosis of pleural malignancies. This review considers the current status of that investigative modality, with particular attention to lesions that are suspected to be mesothelial.

Neuroendocrine neoplasms of the mediastinum

Neuroendocrine neoplasms of the mediastinum form part of a family of tumors characterized by genotypic, immunophenotypic, and functional properties of neuroendocrine differentiation. Although rare, these tumors have been the source of much attention and controversy in the literature. Their nomenclature and classification, in particular, have continued to evolve over the years. Such tumors comprise lesions derived from neuroendocrine elements within the thymus, from paraganglionic rests, or from misplaced embryonal structures within the mediastinum. The most common neuroendocrine neoplasms of this anatomic region, however, correspond to neuroendocrine carcinomas of the thymus. The light microscopic, immunohistochemical, and ultrastructural features of these tumors are reviewed along with the advances in our understanding of these lesions and current trends in nomenclature and terminology.

Cutaneous B-cell lymphoma with signet ring-cell morphology: a clinicopathologic and immunohistochemical study of three cases

Three cases of primary cutaneous B-cell lymphoma with prominent signet ring-cell features are presented. The patients were three men between the ages of 37 years and 74 years (average, 55.5 years). Clinically, the three patients presented with multiple skin nodules. In one patient, the nodules had been present for approximately 5 weeks, although in the two other patients, the nodules were of unknown duration. The lesions were located in the upper extremities (forearm) and measured from 2 cm to 3 cm in diameter. No evidence of lymphadenopathy was observed in any of the patients. Surgical excision of the nodules was performed. Histologically, in two cases, the superficial and deep dermis was replaced by a diffuse cellular proliferation, and in one patient, the tumor cell population adopted a nodular pattern of growth involving adnexal structures and infiltrating the subcutaneous fat. In all cases, the tumors were composed of cells showing signet ring-cell features, with striking indentation of the nuclei toward the periphery of the cell. Immunohistochemical studies using antibodies for B-cell and T-cell markers (L-26 and UCHL) as well as antibodies for leukocyte common antigen, keratin, and kappa and lambda light chains were performed in all cases. The tumor cells showed a positive reaction for leukocyte common antigen, L-26, and lambda light chain restriction. Follow-up information was only available in one patient, who has remained alive and well 2 years after diagnosis without evidence of progression of the disease. The present cases highlight the importance of recognizing this unusual morphologic type of lymphoma so as to arrive at a correct diagnosis.

In situ determination of T-cell receptor beta expression patterns

A definitive diagnosis of T-cell lymphoma may be contingent on the rearrangement profile of the T-cell receptor. This is most accurately done by molecular analysis of the beta-chain of the T-cell receptor (TCR beta) by Southern blotting hybridization that requires unfixed tissue. We describe a reverse transcriptase in situ PCR (RT in situ PCR) method that permits the target-specific direct incorporation of the reporter nucleotide into the different transcripts that comprise the TCR beta, using paraffin-embedded, formalin-fixed tissue. Each of the 25 possible V beta segment rearrangements was documented in three lymph nodes with nonspecific lymphadenitis, with clonal expansion evident in a case of metastatic melanoma. Monoclonal expression was documented in seven tissues diagnostic of a T-cell lymphoma. We analyzed five additional tissues for which a definitive diagnosis of T-cell vs B-cell lymphoma could not be rendered on the basis of histological, immunohistological, and flow cytometric analysis. RT in situ PCR for TCR beta expression with CD3 co-labeling demonstrated which of these lesions was a B-cell-rich T-cell lymphoma. We conclude that the RT in situ PCR methodology will allow the routine determination of monoclonal vs multiclonal expression patterns of the TCR beta using archival paraffin-embedded tissues.(J Histochem Cytochem 49:139-145, 2001)

Immunostaining for thyroid transcription factor 1 and cytokeratin 20 aids the distinction of small cell carcinoma from Merkel cell carcinoma, but not pulmonary from extrapulmonary small cell carcinomas

OBJECTIVE

To study the expression of thyroid transcription factor 1 (TTF-1) and cytokeratin 20 (CK20) in pulmonary small cell carcinomas, extrapulmonary small cell carcinomas, and Merkel cell carcinomas, and thereby determine whether these markers are helpful in distinguishing these 3 groups of small cell neuroendocrine carcinomas.

MATERIALS AND METHODS

Immunostaining for TTF-1 and CK20 was performed in 102 cases of small cell carcinoma (pulmonary, 52; extrapulmonary, 50) and 23 cases of Merkel cell carcinoma. The results for the 3 groups were compared.

RESULTS

Thyroid transcription factor 1 was expressed in 82.7% of pulmonary small cell carcinomas, 42.0% of extrapulmonary small cell carcinomas (range, 33.3--53.3% for the various sites), and 0% of Merkel cell carcinomas. Cytokeratin 20 staining was consistently negative in pulmonary small cell carcinomas, and positive in 4.0% of extrapulmonary small cell carcinomas and 100% of Merkel cell carcinomas.

CONCLUSIONS

Immunostaining for TTF-1, especially when combined with immunostaining for CK20, can aid in the distinction between Merkel cell carcinoma and small cell carcinoma (both pulmonary and extrapulmonary). However, in individual cases, these markers cannot be used to distinguish between pulmonary and extrapulmonary small cell carcinomas due to the extensive overlap in immunophenotypes.

Langerhans' cell histiocytosis of the thymus associated with multilocular thymic cyst

Though Langerhans' cells are a normal component of the thymus, the pathologic entity of Langerhans' cell histiocytosis (LCH) occurs very uncommonly in this organ. The few reports of thymic LCH are nearly all in children or young adults and may or may not be associated with extrathymic clinical disease. Although radiographic descriptions of cyst formation in the thymus in association with LCH have been reported, no examples to our knowledge of thymic LCH have been reported in association with multilocular thymic cyst (MTC). We report a case of thymic LCH in association with an asymptomatic multilocular thymic cyst which was discovered as part of cardiothoracic surgery in a middle-aged man. To our knowledge, this is the first example of MTC occurring in association with thymic LCH. HUM PATHOL 31:1532-1535.

On the histologic heterogeneity of thymic epithelial neoplasms. Impact of sampling in subtyping and classification of thymomas

Six hundred thirty cases of thymomas were evaluated to determine morphologic heterogeneity. The thymomas were grouped in 4 categories using previous terminology. Stratification according to the number of sections available for examination revealed a marked difference in distribution by histopathologic type. A cutoff number of 5 sections appears to provide a difference in subgrouping these tumors. In addition, the proportion of invasive tumors increases with the number of sections examined. Final classification may be affected by the extent of sampling. Histopathologic classification of thymoma, although of academic interest, may have limited practical relevance for assessment of prognosis in limited biopsy tissue. Proper evaluation of histology and aggressive potential in thymoma should be based on ample sampling and assessment of capsular integrity, which is best accomplished on thoroughly sampled resection specimens rather than incomplete or limited biopsy samples.

Recent advances in the application of immunohistochemical markers for the diagnosis of soft tissue tumors

Soft tissue tumors represent a frequent source of diagnostic difficulty for surgical pathologists. Over the past 20 years, immunohistochemical studies have emerged as a powerful and helpful tool for the assessment and characterization of these lesions. Although much progress has been made in this field, the continuous realization of the relative lack of specificity and broad overlap in reactivity for the various tumor markers among these lesions has contributed to limit somewhat their usefulness and reliability in this area of tumor diagnosis. However, with the advent of new markers has come the new promise of better and more accurate distinction and characterization for these tumors. Herein we will review the current status of immunohistochemical tumor markers in the diagnosis of soft tissue neoplasms and address some of the more recently described antibodies and their relative value and limitations for the diagnosis of these tumors.

The role of immunohistochemistry in the diagnosis of malignant mesothelioma

The immunohistochemical diagnosis of mesothelioma is perhaps one of the most perplexing and controversial issues in surgical pathology. A tumor that in essence is extremely rare has managed to captivate the attention not only of pulmonologists and thoracic surgeons but also of pathologists. Throughout its history, mesothelioma has emerged as one of the tumors that has evaded definitive characterization; hence, the numerous attempts at trying to establish not only histological criteria but also histochemical, immunohistochemical, and ultrastructural guidelines for its diagnosis. Perhaps as we enter an era of more sophisticated technology, molecular biology will have an opportunity to make inroads into the diagnosis and characterization of this peculiar neoplasm. Despite the many difficulties involved in the diagnosis of malignant mesothelioma, we have recently gained significant knowledge of this entity in many respects, several decades after its description. From a morphological point of view, several variations of the histological appearances that these tumors may exhibit have been described. Traditional histochemistry and electron microscopy continue to play an important role in the evaluation of these neoplasms, with ultrastructural analysis in particular representing the most reliable technique for making this diagnosis in equivocal cases. However, because of its speed, cost-effectiveness, and general availability, immunohistochemistry has emerged as the most commonly used procedure for the diagnosis of mesotheliomas. We herein present a review of the current status of immunohistochemical evaluation of malignant lesions that are suspected of having a mesothelial lineage.

Neuroendocrine carcinomas (carcinoid tumor) of the thymus. A clinicopathologic analysis of 80 cases

We studied 80 cases of primary thymic neuroendocrine carcinomas. Most patients had symptoms; approximately one third were asymptomatic. All cases were treated by surgical excision. The tumors were divided according to histopathologic features into low- (n = 29), intermediate- (n = 36), and high-grade (n = 15) types. The tumors displayed a variegated histologic appearance and unusual cytologic features. Some cases showed transition from low to high grade within the same tumor mass. Mitotic activity ranged from fewer than 3 to more than 10 mitotic figures per 10 high-power fields, and most tumors displayed marked cellular atypia and areas of necrosis. In 73 patients, the tumor was confined to the anterior mediastinum. Positive immunohistochemical reaction was observed using antibodies for CAM 5.2 low-molecular-weight cytokeratins, broad-spectrum keratin, chromogranin, synaptophysin, and Leu-7. The clinical follow-up obtained in 50 patients correlated well with tumor differentiation. Therefore, the behavior of these tumors seems to correlate with histologic grade, which seems directly proportional to degree of differentiation. We propose replacing the term thymic carcinoid with thymic neuroendocrine carcinoma, which better reflects the aggressive biologic behavior of these tumors in the mediastinal location.

Primary neuroendocrine carcinoma (thymic carcinoid) of the thymus with prominent oncocytic features: a clinicopathologic study of 22 cases

Twenty-two cases of oncocytic thymic neuroendocrine carcinomas (carcinoid tumors) are presented. The patients were 17 men and 5 women between the ages of 26 and 84 years (median, 55 years). Nine were asymptomatic, and the tumor was found on routine examination; four patients presented with chest pain, two with weight loss, two with multiple endocrine neoplasia I syndrome, and one with Cushing's syndrome. Surgical resection of the mediastinal tumor was performed in all cases. The lesions were described as soft, light tan to brown, measuring from 3 to 20 cm in greatest diameter. On cut section, the tumors showed a homogeneous surface, soft consistency, and focal areas of hemorrhage. Microscopically, the lesions were characterized by nests or trabeculae of tumor cells that contained abundant granular to densely eosinophilic cytoplasm, with round to oval nuclei and in some areas prominent nucleoli. Mitotic figures ranged from 2 to 10 per 10 high-power fields; foci of comedonecrosis were seen in all cases. Immunohistochemical studies including broad spectrum keratin, CAM 5.2, chromogranin, synaptophysin, Leu-7, and p53 were performed in 12 cases. All of the tumors were strongly positive for CAM 5.2 low-molecular-weight cytokeratin, 11 showed strong positive reaction for Leu-7, 10 for broad-spectrum keratin, 8 for chromogranin, 7 for synaptophysin, and only 1 case showed focal positive staining of the tumor cells for p53. Clinical follow-up of 14 patients showed that 10 were alive between 2 and 11 years, and 4 patients had died of tumor from 4 to 11 years after diagnosis. Patients with good clinical outcome were those whose tumors showed low mitotic activity and minimal nuclear pleomorphism, whereas those who had died of their tumors were those whose tumors were characterized by marked nuclear atypia and higher mitotic rates. Oncocytic thymic carcinoids should be added to the differential diagnosis of anterior mediastinal neoplasms characterized by a monotonous population of tumor cells with prominent oncocytic features.

Thymic neuroendocrine carcinomas with combined features ranging from well-differentiated (carcinoid) to small cell carcinoma. A clinicopathologic and immunohistochemical study of 11 cases

We reviewed 11 cases of primary thymic neuroendocrine carcinomas with combined features ranging from well-differentiated to poorly differentiated neuroendocrine carcinoma. For 3 asymptomatic patients, tumors were discovered during routine examination. Presentation in the other patients was as follows: Cushing syndrome, 2 patients; chest pain, 3 patients; superior vena cava syndrome, 1 patient; and hypercalcemia and hypophosphatemia, 1 patient. No clinical data were available for the 11th patient. All tumors were located in the anterior mediastinum and treated by surgical excision. The lesions were large and well-circumscribed with areas of hemorrhage and necrosis. They were characterized by areas showing a proliferation of monotonous, round tumor cells adopting a prominent organoid pattern admixed with areas showing sheets of atypical cells with hyperchromatic nuclei, frequent mitoses, and extensive areas of hemorrhage and necrosis. Immunohistochemical studies performed in 6 cases showed strong CAM 5.2 low-molecular-weight cytokeratin positivity in all cases, chromogranin and synaptophysin positivity in 4, Leu-7 in 3, and focal positivity for p53 in 2. Follow-up information for 9 cases showed that all patients died of their tumors between 1 and 4 years after diagnosis. The present cases highlight the heterogeneity of neuroendocrine neoplasms and reinforce the notion that these tumors form part of a continuous spectrum of differentiation.

Pigmented thymic carcinoids: a clinicopathological and immunohistochemical study of two cases

Two cases of pigmented thymic carcinoids are presented. The patients were two men, 32 and 47 years of age. The two patients were asymptomatic and the tumor was discovered on routine chest radiographic evaluation. The tumors were treated by surgical excision in both patients. Grossly, they presented as tan-white tumors without evidence of necrosis or hemorrhage or any visible pigmentation. Histologically, the tumors were characterized by a monotonous proliferation of tumor cells arranged in a trabecular or nesting pattern. The tumor cells showed moderate amounts of pale eosinophilic cytoplasm, round to oval nuclei, and inconspicuous nucleoli. Mitotic activity varied from three to eight per 10 high-power fields. In addition, both tumors showed prominent areas of intra- and extracellular dark pigment deposition. The pigment reacted positively with the Fontana-Masson stain and was negative for iron stain. Immunohistochemical studies performed in one case showed immunoreactivity of the tumor cells for chromogranin, Leu 7, and keratin. Synaptophysin and P53 immunostains were negative. Clinical follow-up was obtained in one patient who was alive and well 10 years after surgical resection. The presence of abundant melanin pigment in thymic carcinoids highlights an important pitfall for diagnosis in these tumors that should be taken into consideration in the evaluation of anterior mediastinal lesions.

Clear-cell epithelioid leiomyoma of the round ligament

A case of clear-cell epithelioid leiomyoma of the round ligament in a 69-year-old woman is described. The neoplasm presented as a firm left inguinal mass. A preoperative computed tomography (CT) scan demonstrated an enhancing lesion extending extra-abdominally from the region of the external inguinal ring. The surgical resection specimen was tan-white, well-circumscribed, and measured 5.8 cm in maximum dimension. Microscopic examination revealed a well-demarcated neoplasm comprised of polygonal cells with abundant clear cytoplasm arranged in clusters and single files with abundant intervening hyalinized stroma. There was minimal nuclear atypia and mitotic figures were rare. Periodic acid-Schiff with diastase demonstrated intracytoplasmic glycogen. Immunohistochemical stains for pan-actin, smooth muscle actin, desmin, bcl-2, and vimentin were positive in the tumor cells, whereas stains for CD34, carcinoembryonic antigen, cytokeratin, epithelial membrane antigen, S100 protein, and neurofilaments were negative. Electron microscopy demonstrated features of smooth muscle differentiation including longitudinally oriented fine filaments with focal condensations, pinocytotic activity, and subplasmalemmal densities. This case illustrates the ubiquitous distribution of epithelioid smooth muscle neoplasms and highlights the potential pitfalls for diagnosis when they occur in an unusual location.

Micronodular thymoma with lymphoid B-cell hyperplasia: clinicopathologic and immunohistochemical study of eighteen cases of a distinctive morphologic variant of thymic epithelial neoplasm

We describe 18 cases of a distinctive morphologic variant of primary thymic epithelial neoplasm characterized by a micronodular growth pattern associated with florid lymphoid follicular hyperplasia of the stroma. The tumors occurred in seven women and 11 men aged 41 to 76 years (mean, 58 years). All cases were asymptomatic and discovered incidentally on routine chest radiograph or during coronary artery bypass surgery. The tumors measured from 3 to 10 cm in greatest dimension and were well circumscribed and encapsulated. In seven cases, the lesions were grossly described as cystic or partially cystic masses. Histologically, they were characterized by a proliferation of small tumor nodules separated by abundant lymphoid stroma with prominent germinal centers. The nodules were composed of spindle cells containing oval nuclei devoid of atypia or mitotic activity. Immunohistochemical studies showed strong positivity of the spindle tumor cells for CAM 5.2 and broad spectrum keratin antibodies. The surrounding lymphoid cell population was strongly positive for LCA and L26 and showed a polyclonal pattern of staining for kappa and lambda. Stains for UCHL-1, CD1a, CD3, CD5, and CD99 were negative in the stromal lymphoid cell population. The tumor in one of the patients was associated with active pulmonary tuberculosis, and in another with anemia and splenomegaly of unknown etiology. None of the patients had clinical signs or history of myasthenia gravis or other autoimmune disorders. The present cases are interpreted as an unusual morphologic variant of spindle cell thymoma with prominent B-cell lymphoid hyperplasia. The possible significance of this phenomenon is discussed.

Angiomatoid neuroendocrine carcinoma of the thymus: report of a distinctive morphological variant of neuroendocrine tumor of the thymus resembling a vascular neoplasm

Three cases of primary thymic neuroendocrine tumors characterized by prominent angiomatoid features that resembled a vascular neoplasm are presented. The patients were all men between 52 and 59 years of age who presented with chest pain and shortness of breath attributable to a large anterior mediastinal mass. The lesions ranged in size from 6 cm to 15 cm in greatest diameter, and were grossly soft and well circumscribed, but not encapsulated. The cut surface was remarkable for multiple blood-filled cyst-like spaces admixed with focal solid, hemorrhagic areas. Histologically, the tumors contained multiple cystically dilated spaces filled with blood which imparted the lesion with a striking angiomatoid appearance. The walls of the cysts were lined by a monotonous proliferation of round to oval cells with distinct cell borders, round central nuclei, and abundant eosinophilic cytoplasm. Mitotic activity was present in all cases and varied from 3 to 8 mitoses per 10 high-power fields. Immunohistochemical studies performed in two cases showed positivity of the tumor cells for keratin, Leu 7, and synaptophysin, and focal chromogranin positivity in one. Follow-up information obtained in two patients showed that both had died of tumor 4 and 8 years after initial diagnosis. The present cases show an unusual morphological appearance of thymic neuroendocrine tumors that may be mistaken for a vascular neoplasm. Immunohistochemical stains may be of importance in such instances in arriving at the correct diagnosis.

Thymoma, atypical thymoma, and thymic carcinoma. A novel conceptual approach to the classification of thymic epithelial neoplasms

Primary thymic epithelial neoplasms have been the subject of much controversy in recent years owing to the difficulties posed by these tumors for precise histopathologic typing and prognostication. A number of classification schemes using different terminology have been proposed, none of which has satisfactorily managed to address all the problems and concerns related to these tumors. We present a proposal for a novel approach to the histologic classification of primary thymic epithelial neoplasms that is based on morphologic features of differentiation. The principle behind this classification scheme is that the determination of the cytologic degree of atypia and the identification of the organotypical features of thymic differentiation may permit accurate classification of these neoplasms into 3 simple and reproducible diagnostic categories: thymoma, atypical thymoma, and thymic carcinoma. We further reiterate the traditional concept that tumor staging, not histopathologic typing, has a more crucial role for accurate and reliable prognostication for the better differentiated forms of these tumors.

Spindle-cell neuroendocrine carcinomas of the thymus (spindle-cell thymic carcinoid): a clinicopathologic and immunohistochemical study of seven cases

Seven cases of spindle-cell neuroendocrine carcinomas (carcinoid tumors) of the thymus are presented. The patients were three women and four men between the ages of 26 and 74 years (median age, 50 yr). The lesions presented as large anterior mediastinal masses on radiographic examination and were treated by surgical excision. Grossly, the tumors were tan-brown and well circumscribed but encapsulated, and they measured from 2 to 15 cm in greatest diameter. Histologically, they were characterized by a dense proliferation of spindle cells that focally adopted a vaguely organoid pattern, with discrete nests of tumor cells separated by thin fibrovascular septa. Mitotic figures were present in all of our cases and ranged from 2 to 8 per 10 high power fields. Focal areas of necrosis were also present in all of the cases. Immunohistochemical studies performed in six cases showed positive staining for chromogranin in five cases, synaptophysin and keratin in four, and Leu 7 in three. Clinical follow-up showed that two patients died of their tumors 6 and 11 years after diagnosis; one was alive 8 years after diagnosis. Spindle-cell neuroendocrine carcinomas of the thymus (spindle-cell thymic carcinoids) should be considered in the differential diagnosis of spindle-cell neoplasms of the anterior mediastinum. Because of their aggressive clinical behavior, it is important to separate them from the other benign or low-grade spindle-cell tumors that are more common at this location.

Spindle cell thymic carcinoma: clinicopathologic and immunohistochemical study of a distinctive variant of primary thymic epithelial neoplasm

We report 16 cases of a distinctive variant of primary thymic epithelial neoplasm characterized by prominent spindling of the tumor cells. The patients were seven women and nine men aged 23 to 82 years (mean, 54 years). The lesions presented as anterior mediastinal masses without clinical or radiographic evidence of tumor elsewhere. Most patients had chest pain, dyspnea, and cough; in five patients, the tumors were asymptomatic and were discovered on routine clinical examination. Grossly, the lesions were firm, well-circumscribed, and locally infiltrative, and had a firm cut surface with foci of hemorrhage, necrosis, and cystic changes. Most of the tumors were treated by complete surgical excision. Histologically, they were characterized by a spindle cell proliferation showing varying degrees of atypia and mitotic activity. In 12 cases, transitions could be seen with areas that showed the features of conventional spindle cell thymoma. In two cases, areas showing features of poorly differentiated (lymphoepitheliomalike) carcinoma and anaplastic carcinoma could also be observed. Immunohistochemical studies in 10 cases showed strong positivity of the spindle tumor cells for CAM5.2 cytokeratin, and negative staining for a panel of antibodies including epithelial membrane antigen, carcinoembryonic antigen, actin, desmin, vimentin, S-100 protein, HMB45, CD34, CD5, and CD99. Clinical follow-up of eight patients showed an aggressive biologic behavior with recurrence, metastasis, and death by tumor in five of them 2 to 5 years after diagnosis. Based on these findings, the present tumors are interpreted as an unusual spindle cell variant of thymic carcinoma. The close association of these cases with areas showing the features of spindle cell thymoma within the same tumor mass suggests that some of these lesions may arise as a result of malignant transformation in a preexisting spindle cell thymoma.

Tumors of the skin composed of large cells with abundant eosinophilic cytoplasm

Tumors of the skin composed of large epithelioid cells displaying abundant smooth or granular eosinophilic cytoplasm are relatively rare, yet may constitute a source of diagnostic difficulties for pathologists. Lesions derived from various skin elements are represented in this group, including tumors originating from adnexal structures and connective tissue elements of the dermis. The large, pink-cell or epithelioid appearance of the tumor cells may be the result of attempts to recapitulate the phenotype of a cell line normally characterized by such morphological appearance, such as apocrine epithelium, or may result from secondary changes in the cytoplasm of the tumor cells, such as accumulation of autophagosomes in granular cell tumors. The characteristic pathological features of this group of tumors is the subject of this review, with special emphasis on their differential diagnosis and the morphological features that may be of help for practicing pathologists to arrive at a correct diagnosis.

Balloon cell change in cellular blue nevus

Balloon cells are altered melanocytes with clear vacuolated cytoplasm caused by a defect in the process of melanogenesis. Although rare, balloon cell change has been observed in a variety of melanocytic proliferations, particularly intradermal melanocytic nevi and melanoma. When present, such features may lead to difficulties in diagnosis, particularly with other clear cell neoplasms. We report an unusual case of the development of balloon cell change in a cellular blue nevus, a phenomenon that has not been extensively addressed in the literature. The importance of recognizing this change in cellular blue nevus to avoid misinterpreting the lesion as malignant is discussed.

Idiopathic fibroinflammatory (fibrosing/sclerosing) lesions of the mediastinum: a study of 30 cases with emphasis on morphologic heterogeneity

The clinicopathologic and immunohistochemical findings in 30 cases of idiopathic fibroinflammatory lesions of the mediastinum are presented. There were 17 male and 13 female patients between 10 and 64 years of age; 19 were African-American, and 10 were Caucasian. Clinically, respiratory and/or systemic symptoms including cough, shortness of breath, and fever were present in 28 patients. Five patients also presented with evidence of superior vena cava syndrome. All of the lesions involved the anterior mediastinum with radiographic evidence of hilar and paratracheal involvement in nine and five patients, respectively. Histologically, the lesions were characterized by an inflammatory fibrosing process that showed three distinctive histologic patterns. On the basis of the histologic pattern, they were subdivided into three distinct groups (stages). Stage I demonstrated edematous fibromyxoid tissue with numerous spindle cells, eosinophils, mast cells, lymphocytes, plasma cells, and thin-walled blood vessels; Stage II showed thick glassy bands of haphazardly arranged collagen with focal interstitial spindle cells, lymphocytes, and plasma cells; and Stage III was characterized by dense acellular collagen with scattered lymphoid follicles and occasional dystrophic calcification. Immunohistochemical studies in 17 cases highlighted large numbers of vimentin- and actin-positive spindle cells and capillary-like vessels in Stage I lesions, with fewer numbers of vimentin-positive, actin-negative spindle cells and vessels in Stage II lesions. Our findings suggest that "sclerosing mediastinitis" represents the final stage of an evolving, dynamic process with different morphologic appearances akin to abnormal wound healing. Thus, we propose the term fibroinflammatory lesion of the mediastinum to convey the true nature of the process.

Primary thymic epithelial neoplasms: spectrum of differentiation and histological features

Primary thymic epithelial neoplasms have been the source of much controversy over the years because of difficulties in their histopathologic classification and prognostication of clinical behavior. Despite recent advances in our understanding of the immunopathology and molecular pathology of these neoplasms, no universally accepted system of classification is yet available for these tumors. A variety of classification schemes have been proposed in the past based on either morphological, histogenetic, or immunophenotypic considerations. For the most part, the majority of such classifications have been merely descriptive with little value for prognostication, or have proven cumbersome and difficult to apply in clinical practice. Recent studies have shown that primary thymic epithelial neoplasms, rather than representing several discrete, separate entities constitute part of a continuous spectrum of differentiation ranging from well-differentiated neoplasms to poorly-differentiated neoplasms. Based on these observations, a novel classification of primary thymic epithelial neoplasms has been proposed that divides these tumors into three easily reproducible diagnostic categories based on their degrees of differentiation: thymoma, atypical thymoma, and thymic carcinoma (corresponding to well-differentiated, moderately-differentiated, and poorly-differentiated neoplasms, respectively). The histopathologic features and diagnostic criteria for these tumors is the subject of this review.