Histologic classification of thymoma: the World Health Organization and beyond

Thymoma classification has remained for many years a troubled and contentious field. In recent years, the World Health Organization (WHO) presented a proposal for the histopathologic classification of thymic epithelial neoplasms that has been adopted as the standard by many pathologists throughout the world. Yet, controversy still exists regarding its validity, accuracy, usefulness, and reproducibility in routine clinical practice. This article reviews the basic criteria of the current WHO classification of thymoma, along with its weaknesses and limitations, and presents alternate proposals for the histopathologic approach to the classification of thymic epithelial neoplasms.

Evidence-Based Pathology and the Pathologic Evaluation of Thymomas: Transcapsular Invasion Is Not a Significant Prognostic Feature

Context.—Evaluation of transcapsular invasion is currently considered very important in the pathologic examination of thymomas. However, recent studies have questioned the prognostic value of stratifying thymoma patients into stage I and II disease. Evidence-based pathology promotes the use of systematic reviews of literature and meta-analysis of data to synthesize the results of multiple publications.

Objective.—To analyze the data in the literature regarding the prognostic importance of transcapsular invasion in thymoma stage I and II.

Design.—A systematic review of the English literature was carried out for “thymoma,” “stage,” and “prognoses.” Case reports, case series with fewer than 10 cases, and studies with follow-up periods shorter than 5 years were excluded. Twenty-one retrospective publications reporting the experience with 2451 thymomas were selected for review, including 1419 stage I and 1032 stage II patients. Meta-analysis was performed, and possible publication bias was studied with funnel plots of precision and various statistics.

Results.—Meta-analysis yielded no significant differences in disease-free or overall survival rates in stage I and II thymoma patients. Funnel plots of precision and statistical tests such as the Egger regression intercept test showed no significant publication bias.

Conclusions.—The lack of significant differences in the prognosis of patients with stages I and II thymoma suggests that evaluation of transcapsular invasion is of no clinical value in tumors that lack invasion of neighboring organs or the pleura. The data regarding the prognosis of stage II thymoma patients is somewhat heterogenous, with only some individuals having been treated with radiation therapy, suggesting the need for future randomized controlled trials.

Metastases to soft tissue: a review of 118 cases over a 30-year period

BACKGROUND

Metastatic tumors presenting as soft tissue masses are relatively rare and can be the source of diagnostic confusion both clinically and pathologically. The authors' experience was reviewed at a large academic medical center over a 30-year period (1971-2000) with metastases to soft tissue.

METHODS

The tumors in the study included mainly lesions involving skeletal muscle or skeletal muscle and subcutaneous tissue of the upper and lower limbs, trunk, shoulders, and buttocks. Direct extension from tumors originating in bone or adjacent organs, tumors involving the skin or areas known to contain abundant lymph nodes (ie, axilla, groin), and hematopoietic malignancies were excluded.

RESULTS

One hundred and eighteen cases were identified; 60 patients were women and 58 were men. The age range was 20 to 87 years (median of 53.5 years). The primary tumor was located in the skin (19 patients), lung (13 patients), breast (13 patients), kidney (12 patients), colon and rectum (12 patients), uterus (8 patients), ovary (5 patients), head and neck (tongue, pharynx, larynx, nasal cavity, and mandible) (5 patients), esophagus (2 patients), stomach (2 patients), cervix (2 patients), small bowel (2 patients), bone (2 patients), adrenal gland (1 patient), eye (1 patient), testis (1 patient), urinary bladder (1 patient), and salivary gland (1 patient). In 27% (32 of 118 cases) of cases, the soft tissue metastasis was the initial manifestation of the disease. In 13.5% (16 of 118 cases) of cases the primary site of origin could not be identified. The sites of metastasis included the abdominal wall (25 patients), back, including scapular region (20 patients), thigh (17 patients), chest wall (15 patients), arm (15 patients), shoulder (11 patients), buttock (5 patients), perineum (3 patients), leg (2 patients), foot (1 patient), umbilical area (1 patient), ankle (1 patient), scalp (1 patient), and elbow (1 patient). The histologic classification of the tumors included carcinoma (83 patients), malignant melanoma (20 patients), sarcoma and carcinosarcoma (9 patients), malignant mixed Mullerian tumor (2 patients), seminoma (1 patient), malignant teratoma (1 patient), malignant gastrointestinal stromal tumor (1 patient), and neuroblastoma (1 patient). Many of the tumors displayed histologic features that created difficulties for diagnosis and could be easily mistaken on routine histopathologic examination for a variety of primary soft-tissue sarcomas. Routine use of immunohistochemical stains aided in their proper recognition.

CONCLUSIONS

Metastases are not an infrequent finding in soft tissue and they may represent the initial manifestation of the disease. Use of a basic panel of immunohistochemical stains is recommended for defining the cell type and arriving at the correct diagnosis.

Unusual non-neoplastic lesions of the lung

Many nonneoplastic conditions that may affect the lung are in reality rare or unusual manifestations of metabolic processes, inflammatory conditions, or unknown etiology. Because of their rarity, they can often be confused with malignant neoplasms. Familiarity with these conditions not only will expedite further treatment for these patients but also will avoid the process of more tests or unnecessary surgical procedures. The nomenclature for some of those conditions is still controversial. The clinical outcome of these conditions can be quite variable, with some patients surviving a long number of years and others eventually succumbing to the disease. We will limit our discussion in this review to four of these conditions, including inflammatory pseudotumor (inflammatory myofibroblastic tumor), placental transmogrification of lung, alveolar microlithiasis, and metastatic calcification. Although these lesions are not part of the gamut of neoplastic conditions affecting the lung, they are nonetheless important to recognize, as their outcome may not necessarily be an innocuous one.

Lymph node involvement by Langerhans cell histiocytosis: a clinicopathologic and immunohistochemical study of 20 cases

Twenty cases of Langerhans cell histiocytosis (LCH) involving lymph nodes with no other sites of disease are presented. The patients were 12 men and 8 women between 3 months and 68 years of age. Seven patients were younger than 11 years; the other 13 patients were older than 16 years. Clinically, all patients presented with lymphadenopathy and underwent excisional biopsy; clinical and imaging studies did not reveal abnormalities in other organs. Cervical lymph nodes were most commonly involved; other lymph nodes involved included axillary, inguinal, and supraclavicular. Histologically, LCH in lymph nodes had 3 main architectural patterns: (1) preserved nodal architecture with subtle involvement, (2) subtotal effacement of nodal architecture, and (3) total effacement of nodal architecture. There was a gradient of involvement by LCH from focal sinus involvement to diffuse sinus involvement and from focal paracortical involvement to diffuse paracortical involvement. In some cases, focal involvement was initially unrecognized because of the subtle nature of the changes in the lymph node, posing difficulties for diagnosis. Langerhans cells in the involved areas showed strong positivity by immunohistochemical studies for S100 protein and CD1a in all 11 cases assessed. In conclusion, LCH can initially manifest clinically with involvement limited to lymph nodes. Recognition of the different patterns of LCH, particularly cases with subtle involvement, is important for recognizing this disease and separating LCH from other more common causes of lymphadenopathy.

Identification of a novel noncoding RNA gene, NAMA, that is downregulated in papillary thyroid carcinoma with BRAF mutation and associated with growth arrest

In search of tumor suppressor genes in papillary thyroid carcinoma (PTC), we previously used gene expression profiling to identify genes underexpressed in tumor compared with paired unaffected tissue. While searching for loss of heterozygosity (LOH) in genomic regions harboring candidate tumor suppressor genes, we detected LOH in a approximately 20 kb region around marker D9S176. Several ESTs flanking D9S176 were underexpressed in PTC tumors, and for one of the ESTs, downregulation was highly associated with the activating BRAF mutation V600E, the most common genetic lesion in PTC. A novel gene, NAMA, (noncoding RNA associated with MAP kinase pathway and growth arrest) containing the affected EST was cloned and characterized. NAMA is weakly expressed in several human tissues, and the spliced forms are primarily detected in testis. Several characteristics of NAMA suggest that it is a nonprotein coding but functional RNA; it has no long open reading frames (ORFs); the exons exhibit low sequence identity in the evolutionarily conserved regions; it is inducible by knockdown of BRAF, inhibition of the MAP kinase pathway, growth arrest and DNA damage in cancer cell lines. We suggest that NAMA is a noncoding RNA associated with growth arrest.

Germ Cell Tumors With Sarcomatous Components

The clinicopathologic features of 46 patients with germ cell tumors with sarcomatous components (GCTSC) involving either the primary site or their metastases were studied. There were 43 men and 3 women aged 17 to 74 years. Twenty-three tumors arose in the mediastinum, 2 in the retroperitoneum, and 21 in the gonads. The germ cell component consisted of pure mature or immature teratoma (23 cases), teratoma mixed with other seminomatous or nonseminomatous components (17), pure seminoma (2), intratubular germ cell neoplasia (1), and yolk sac tumor (1). The SC included embryonal rhabdomyosarcoma (29), angiosarcoma (6), leiomyosarcoma (4), undifferentiated sarcoma (3), myxoid liposarcoma (1), malignant peripheral nerve sheath tumor (1), malignant "triton" tumor (1), and epithelioid hemangioendothelioma (1). Immunohistochemical studies were carried out in 34 cases with appropriate results supporting the diagnoses. Metastases containing both GCT and SC were observed in 6 cases, metastases of SC alone in 4, and metastases containing only GCT elements in 3. All patients were treated by cisplatinum-based chemotherapy plus other agents followed by surgery. Clinical follow-up was available in 40 patients (1 to 96 mo; mean=24 mo). Thirty-two of 40 patients either died of tumor (25/40; 62.5%) or were alive with advanced, progressive disease (7/40; 17.5%), and only 8/40 (20%) were alive and free of disease between 5 to 40 months (mean=18 mo). Comparison of these patients with an age-matched and stage-matched control group of patients with GCT without SC showed statistically significant differences in survival between the 2 cohorts (P <or=0.001). On the basis of our findings, the presence of SC appears to represent a poor prognostic sign for GCTs of gonadal and extragonadal origin.

Neuroendocrine carcinomas (carcinoid, atypical carcinoid, small cell carcinoma, and large cell neuroendocrine carcinoma): current concepts

Neuroendocrine carcinomas are ubiquitous neoplasms that may occur anywhere in the human body. A unifying concept regarding the classification of these tumors has been controversial. Although most neuroendocrine neoplasms occur in the gastrointestinal tract, current concepts regarding classification and nomenclature are being driven by studies of thoracic tumors. One issue that has been put forward to keep separate nomenclatures for these tumors in different organ systems is the different clinical behavior of these neoplasms in different systems. The most important aspect regarding this group of tumors is the fact that they should be considered neoplasms capable of local recurrence and distant metastasis. Close clinical correlation and appropriate treatment are important to improve the survival rate in this group of patients.

Signet ring cell gastric schwannoma: report of a new distinctive morphological variant

An 89-year-old woman was seen for indigestion, light chest pain, and melanotic stools. Endoscopic examination revealed 2 submucosal gastric masses. A subtotal gastrectomy showed 2 submucosal masses in the stomach: one infiltrating through the muscularis propria into the serosa, the second one, a well-circumscribed submucosal nodule. Histologic examination showed large tumor cells infiltrating diffusely through the muscularis propria into the subserosa. On higher magnification, numerous signet ring cells were present against a myxoid stroma, in addition to large vacuolated epithelioid cells. There was no evidence of invasion, necrosis, nuclear pleomorphism, or mitotic activity. Initial diagnostic considerations based on the histology included signet ring cell carcinoma, malignant melanoma, and a myxoid mesenchymal tumor, including gastrointestinal stromal tumor. A panel of immunohistochemical stains showed diffuse strong positivity for S-100 protein and negative reaction for CD117, bcl-2, cytokeratin AE1/AE3, Melan-A, HMB45, smooth muscle antigen, and other differentiation markers. Electron microscopic examination revealed elongated, complex, and interdigitating cell processes covered by a thin layer of continuous basement membrane material characteristic of peripheral nerve sheath differentiation. The presentation of this tumor was significant in that it was multifocal and infiltrative, mimicking a malignant neoplasm. The extensive myxoid/signet ring cell change represents a heretofore-unreported histologic variant of gastric schwannoma.

Pilot study of rosiglitazone therapy in women with breast cancer: effects of short-term therapy on tumor tissue and serum markers

PURPOSE

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a steroid nuclear receptor that is activated by natural compounds such as specific fatty acids and synthetic drugs such as thiazolidinedione antidiabetic agents. Expressed in normal and malignant mammary epithelial cells, activation of PPARgamma is associated with antiproliferative effects on human breast cancer cells in preclinical studies. The purpose of this study was to test the hypothesis that PPARgamma ligand therapy might inhibit tumor growth and progression in human breast cancer.

EXPERIMENTAL DESIGN

We conducted a pilot trial of short-term (2-6 weeks) treatment with the thiazolidinedione rosiglitazone in 38 women with early-stage (T(is)-T(2), N(0-1), M(0)) breast cancer, administered between the time of diagnostic biopsy and definitive surgery.

RESULTS

Short-term treatment with rosiglitazone (8 mg/d) did not elicit significant effects on breast tumor cell proliferation using Ki67 expression as a measure of cell proliferation and surrogate marker of tumor growth and progression. In pretreatment tumors notable for nuclear expression of PPARgamma by immunohistochemistry, down-regulation of nuclear PPARgamma expression occurred following rosiglitazone administration (P = 0.005). No PPARG mutations were identified, and the incidence of P12A and H446H polymorphisms did not differ relative to U.S. controls (P = 0.5). Treatment with rosiglitazone resulted in increased serum adiponectin (P < 0.001), decreased insulin levels (P = 0.005), and increased insulin sensitivity (P = 0.004). Rosiglitazone was well tolerated without serious adverse events.

CONCLUSION

Our data indicate that short-term rosiglitazone therapy in early-stage breast cancer patients leads to local and systemic effects on PPARgamma signaling that may be relevant to breast cancer.

Diffuse Pulmonary Meningotheliomatosis

Minute pulmonary meningothelial nodules are rare lesions histologically composed of small nests of epithelioid cells located within the interstitium of the lung. These nodules are generally asymptomatic and are usually found incidentally at autopsy or in surgical specimens resected for unrelated causes. The lesions are most often single, although multiple lesions with unilateral involvement of one or even all lobes of the same lung have been described. To our knowledge, cases of meningothelial nodules with disseminated bilateral pulmonary involvement associated with clinical symptoms of restrictive pulmonary disease and radiologic evidence of diffuse reticulonodular pulmonary infiltrates have not been previously documented. We have studied 5 patients presenting with diffuse bilateral pulmonary involvement by numerous minute pulmonary meningothelial nodules. The patients were 4 women and a man aged 54 to 75 years who presented clinically with dyspnea and shortness of breath and the lesions were discovered on open lung biopsies performed for the evaluation of diffuse bilateral interstitial lung infiltrates found on chest x-rays and computed tomography scans. In 3 patients, there was a previous history of malignancy and the radiologic findings were suspected of representing diffuse metastatic disease. Histologically, the lesions were composed of small clusters of epithelioid cells with round to oval nuclei devoid of atypia and surrounded by abundant eosinophilic cytoplasm. Immunohistochemical studies showed positivity of the tumor cells for epithelial membrane antigen and vimentin, and negative staining for cytokeratin, actin, S-100 protein, CD34, chromogranin, and synaptophysin. Electron microscopic examination in 1 case confirmed the ultrastructural features of meningothelial cells, including complex cytoplasmic interdigitations joined by well-developed desmosomes and abundant intracytoplasmic intermediate filaments. The diffuse bilateral involvement of lung parenchyma in the present cases can lead to confusion on clinical and radiologic grounds with a variety of interstitial pulmonary processes, including idiopathic interstitial pneumonia and lymphangitis carcinomatosa. Diffuse pulmonary meningotheliomatosis should be considered in the clinical differential diagnosis of diffuse interstitial pulmonary infiltrates.

Malignant mesothelioma: current status of histopathologic diagnosis and molecular profile

Malignant mesothelioma of the pleura is a relatively rare neoplasm that has been estimated to account for 20 deaths per million males per year in North America and Europe. A causative association has been well established with asbestos exposure. Paradoxically, the incidence of this tumor continues to rise despite public efforts to reduce, contain or eliminate exposure to asbestos fibers over the past few decades. Another paradoxical feature of the disease is that the majority of malignant mesotheliomas represent morphologically low-grade, well-differentiated neoplasms, yet they follow a relentlessly aggressive and virtually uniformly fatal outcome. For this reason, identification of clinical, morphologic, immunohistochemical or molecular genetic parameters is of extremely limited value for prognostication. Surprisingly, for a disease that currently has no known cure, one of the major problems still lies in establishing the correct diagnosis. Diagnosis acquires a particular relevance in light of the medicolegal ramifications of this disease, and diagnosis of malignant mesothelioma is still fraught with difficulties. Despite the advances in modern diagnostic techniques, no specific markers or morphologic features exist that are exclusive to these tumors. Herein, the current status of malignant mesothelioma diagnosis is reviewed, including the possible contributions of modern molecular techniques for their diagnosis.

The Toker Tumor

Primary neuroendocrine carcinoma of the skin is a relatively rare tumor that was first described by Cyril Toker in 1972. Since the seminal paper by Toker based on simple morphologic observations and detailed clinical correlation, our understanding of the clinical, morphological, and biological attributes of these lesions has grown exponentially with their increased awareness by pathologists and clinicians as well as with the many contributions of modern diagnostic techniques. The present review focuses principally on the various morphologic appearance that these tumors are able to adopt, the role of modern special techniques for diagnosis, and the conditions that need to be considered in their differential diagnosis.

Applications and limitations of immunohistochemistry in the diagnosis of malignant mesothelioma

Malignant mesothelioma is an uncommon malignant epithelial neoplasm originating from the serosal surface of body cavities. Because serosal surfaces are a common site of metastatic spread for a variety of malignant neoplasms originating from internal organs, separating malignant mesothelioma from metastatic tumors is of clinical importance. The diagnosis of malignant mesothelioma is complex and usually requires a multimodal approach that includes careful clinical history and physical examination, imaging studies, and tissue sampling for multimodal evaluation including routine histology, histochemistry, electron microscopy, and immunohistochemical tests. Of these, immunohistochemistry has emerged as the most valuable and readily available modality for the routine evaluation of these tumors. Unfortunately, no specific antibodies have yet been developed that can be accepted as exclusive for these tumors. The immunohistochemical diagnosis of malignant mesothelioma therefore depends on the use of a panel of stains that includes markers that are commonly expected to react with these tumors ("positive" markers) and markers that are not commonly expected to react with these tumors ("negative" markers). Additionally, the selection and utility of these various markers can vary considerably based on a constellation of circumstances, including patient sex, histologic appearance of the tumor (ie, epithelioid vs. sarcomatoid, etc), and various other clinical circumstances. Herein, we will review the currently available immunohistochemical markers used for the diagnosis of malignant mesothelioma and offer suggestions for the use of appropriate panels of stains based on specific morphologic types and clinical circumstances.

Myxopapillary ependymoma of the posterior mediastinum

A left paravertebral mass discovered incidentally on routine examination in a 39-year-old woman is described. Computerized tomography studies revealed a 7 x 6 cm, well circumscribed, noncalcified soft tissue mass with lobular borders abutting the left inferior pulmonary vein and descending aorta. It was not possible to determine the exact anatomic location of the mass based on the imaging studies as both peripheral lung tumors and posterior mediastinal lesions may exhibit the imaging findings described here. At thoracotomy, the mass was seen to be well circumscribed, focally attached to the pleura but without involvement of lung parenchyma, and situated in the left posterior mediastinum. On histological examination, the lesion showed the classical features of myxopapillary ependymoma. Immunohistochemical studies confirmed this impression by demonstrating strong positivity of the tumor cells for S-100 protein, glial fibrillary acidic protein, and CD99 and negative staining with other differentiation markers. A review of the literature with a discussion of the histologic and radiologic differential diagnosis of these lesions is presented.