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

Neuroendocrine tumors of the thymus and mediastinum

Neuroendocrine tumors of the thymus (tNET) and mediastinum are very rare neoplasms with scarce available data. All subtypes [typical and atypical carcinoid tumors (TC and AC), large cell neuroendocrine and small cell carcinoma (SCC)] observed elsewhere in the body occur also in the mediastinum and show only few if any organ-specific morphological differences. Although all available data suggest that the broad principles that govern the biology (and hence) the classification of these tumors in general apply also to tNET, there are a few noteworthy peculiarities related e.g., to risk factors, relative frequency and also to molecular genetic features. In this review, we will briefly summarize current knowledge on tNET with a special emphasis on shared and private features in comparison e.g., with pulmonary NET, which have traditionally been regarded the next closely related NET group.

Atypical carcinoid with prominent mucinous stroma: a hitherto unreported variant of pulmonary neuroendocrine tumor

Carcinoid tumors of the lung may show several growth patterns and cell types. We report here a previously undescribed case of primary pulmonary atypical carcinoid with prominent mucinous stroma, an exceedingly rare variant of carcinoid tumor so far reported only in the thymus. The tumor was discovered in a 50-year-old, non-smoker woman, and pursued an aggressive behavior. The lack of TTF-1 expression and the positive staining with hormonal receptors made the diagnosis very challenging. Differential diagnosis with other primary and metastatic mucin-rich tumors is also discussed.

Mucinous adenocarcinomas of the thymus: report of 2 cases and review of the literature

BACKGROUND

Most adenocarcinomas of the mediastinum are metastatic lesions. Primary thymic adenocarcinomas are extremely rare neoplasms. We could find only 12 cases reported in the literature; of these 12, only 4 were of the mucinous subtype.

DESIGN

We report 2 additional cases of the mucinous subtype, including a previously unreported mucinous variant with numerous psammoma bodies.

RESULTS

The first case in a 61-year-old woman resembled a mucinous (colloid) carcinoma of other organs such as the breast and colon. It consisted of islands and strips of tumor cells floating in large pools of extracellular mucin. A unique feature of this tumor was the presence of numerous psammoma bodies. Immunohistochemically, the tumor cells were positive for cytokeratin (CK) 7 and negative for CD5. The second case in an 82-year-old woman was a mucinous adenocarcinoma arising from a thymic cyst with areas of transition from benign to dysplastic epithelium. The tumor cells formed dilated glands, cords, and small nests that infiltrated the thymic cyst wall and exhibited evidence of mucin production. Immunohistochemically, the tumor cells were positive for CK 7 and focally positive for both CD5 and CK 5/6.

CONCLUSIONS

Mucinous adenocarcinoma, with or without, psammoma bodies, may be of primary thymic origin and should be considered in the differential diagnosis of malignant mediastinal tumors. These 2 cases provide further documentation of the rare occurrence of primary mucinous adenocarcinomas of the thymic gland.

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.

Thymic carcinoma: update of current diagnostic criteria and histologic types

Thymic carcinomas are rare tumors thought to derive from thymic epithelium. Because of the complex embryological origin of the thymus, whose development includes contributions from the third and, to a lesser extent, the fourth pharyngeal pouches, thymic carcinomas are endowed with great morphologic heterogeneity. A large number of histologic types have been described that resemble tumors arising in other organs. Unfortunately, no definitive pathognomonic histological features or immunohistochemical markers are associated with these tumors, making them a real challenge for diagnosis. Because of their close similarity with tumors arising at other organs, the diagnosis of thymic carcinoma must be regarded, for the most part, as a diagnosis of exclusion. This review will focus on current criteria for diagnosis of these tumors, with a review of the various histopathologic appearances that they can adopt.

Cystic well-differentiated neuroendocrine carcinoma (carcinoid tumor): a clinicopathologic and immunohistochemical study of two cases

Two cases of primary neuroendocrine carcinoma (carcinoid tumor) arising in the walls of a multilocular thymic cyst (MTC) are described. The patients were 2 men, ages 36 and 44 years. Clinically, the patients had chest pain, cough, and dyspnea. Radiographic evaluation demonstrated the presence of anterior mediastinal tumor in both patients, and complete surgical resection of the tumor mass was performed. The tumors measured approximately 6 and 8 cm in greatest dimension and were cystic with solid areas but did not show areas of necrosis or hemorrhage. Histologic examination revealed a cystic tumor with features similar to those previously described for MTCs. In addition, in the walls of the cystic structures, there was cellular proliferation arranged in a nesting growth pattern, similar to the more solid areas of the tumor. The tumor was characterized by a homogenous cellular proliferation with mild cellular atypia and no more than 2 mitotic figures per 10 high-power fields. Immunohistochemically, the tumor cells showed strong positive reactions for keratin and neuroendocrine markers, ie, chromogranin and synaptophysin. Both patients were alive after periods of 12 and 18 months.

Thymic carcinoid with mucinous stroma: a rare variant of carcinoid with an aggressive clinical course

One variant of thymic carcinoid has prominent mucinous stroma first reported in 1995. We describe such a case characterized by abundant stromal mucin resulting in a histologic picture resembling of metastatic mucinous adenocarcinoma. This variant seems to behave in an aggressive fashion and should be under the differential diagnoses of mediastinal neoplasm with prominent mucin production.

Primary neuroendocrine carcinomas of the mediastinum: review of current criteria for histopathologic diagnosis and classification

Primary neuroendocrine neoplasms occurring in the mediastinum are rare. The spectrum of such tumors can range from low- to high-grade neoplasms. The histogenesis of these tumors is varied, and some of them may originate from ectopic tissues in the mediastinum whereas others represent tumors native to the thymus. Primary thymic neuroendocrine carcinomas therefore need to be separated from other neuroendocrine neoplasms of the mediastinum, namely ectopic parathyroid tumors and paragangliomas. The histopathologic classification of primary neuroendocrine carcinomas of the mediastinum is still under debate and continues to be controversial, as is attested to by the different publications on the topic. Some authors continue to use old terms such as "carcinoid" and "atypical carcinoid" to designate these lesions, whereas others favor the use of a more unifying nomenclature that acknowledges the malignant nature of these lesions, namely that of neuroendocrine carcinoma. However, one aspect that all agree on is that, when they occur in the thymic region, these tumors should be considered as aggressive neoplasms capable of local recurrence and distant metastasis. This review will center on the morphologic spectrum of neuroendocrine carcinomas of the thymus, with special emphasis on diagnostic features and criteria for classification.

Adenocarcinoma of the thymus: mucinous subtype

Primary thymic adenocarcinoma, mucinous subtype, is extremely rare with only one case reported to date. We describe herein a case of thymic mucinous adenocarcinoma. A 59-year-old man was identified to have an anterior mediastinal tumor and was diagnosed as mucinous adenocarcinoma. Clinical and radiographic examinations disclosed no evidence of tumor elsewhere. The patient received radiotherapy, but the general condition deteriorated and died 11 months after tumor detection. Thoracic autopsy revealed an anterior mediastinal tumor measuring greater than 10 cm, uncapsulated, and white. The tumor had clear margins and was clearly isolated from the lung. Histologically, the tumor demonstrated papillary, acinar, and cribriform structure and produced abundant extracellular mucin. Immunohistochemically, most tumor cells were positive for cytokeratin 7, were partially positive for CD5, and were negative for TTF-1, Sp-A, CDX-2, MUC2, napsin A, and cytokeratin 20. Collectively, the diagnosis of the tumor was primary mucinous adenocarcinoma of the thymus. We propose that the mucinous subtype should be recognized as one of the histopathological entities of thymic adenocarcinoma.

Adenocarcinoma of the thymus: report of two cases, including a previously undescribed mucinous subtype

We report two cases of primary thymic adenocarcinoma, a very uncommon neoplasm with limited information in the literature. Both patients were men (age 15 and 39 years). The first case was a mucinous carcinoma, a subtype of adenocarcinoma not previously recognized in the thymus. It comprised islands and strips of mucin-rich tumor cells floating in large pools of extracellular mucin. There was transition of carcinomatous epithelium to the attenuated epithelium of a thymic cyst. Immunostaining for high molecular weight cytokeratin furthermore highlighted in one area negatively stained tumor islands wrapped by positively stained residual thymic medullary epithelium, suggesting in situ origin of the carcinoma from the thymic epithelium. The second case was a papillary carcinoma with high nuclear grade and many psammoma bodies. It showed strong immunoreactivity for CD5 and did not stain for CA-125 as well as thyroid, pulmonary, and mesothelial markers. The findings in this study therefore broaden the morphologic spectrum of thymic adenocarcinomas to include a mucinous subtype. Review of the literature indicates that thymic adenocarcinomas usually arise from thymic cyst or type A thymoma, and the clinical outcome is variable.

Neuroendocrine carcinoma (carcinoid) of the thymus associated with Cushing's syndrome

Neuroendocrine carcinoma (carcinoid) of the thymus associated with Cushing's syndrome is a rare disease. Recent evidence suggests that these tumors form part of a continuous spectrum ranging from well-differentiated carcinomas to small cell carcinomas. We report two new cases and review the 23 cases reported in the literature since 1972. The different diagnostic modalities are discussed, and an algorithm for the diagnosis of ectopic secretion of adrenocorticotropin (ACTH) is presented. In the future, the advent of radiologic and nuclear imaging as well as more accurate workup should help to diagnose these tumors at an earlier stage and improve the long-term outcome.

Clinicopathologic and DNA cytometric analysis of carcinoid tumors of the thymus

Twelve cases of carcinoid tumors of the thymus were reviewed in terms of clinicopathologic, histochemical, and immunohistochemical features and DNA ploidy patterns. The collective consisted of nine male and three female patients, aged 34 to 74 years, of whom five (42%) had symptoms. Eleven patients underwent surgical resection, and one with systemic metastases was autopsied. In the 11 resected patients, tumors had invaded surrounding structures in four cases, and mediastinal lymph node metastases were detected in six. Recurrence occurred in two of the resected patients (18%), and the 5-year survival rate was 82%. Histologically, all tumors showed an organoid growth pattern with delicate fibrovascular stroma. In addition, three tumors had unusual morphologic features such as combined features of carcinoid tumor and thymoma and solid growth pattern with occasional large tumor cells. Mitotic counts ranged from 1 to 14 per 10 high-power fields with a mean count of 4.9. Central necrosis within solid nests was observed in nine tumors. Classification of this series using the WHO histologic classification system resulted in categorization of all 12 tumors as atypical carcinoids. All tumors were positive for Grimelius staining and for cytokeratin. Immunohistochemical staining documented the presence of moderately to strongly positive neuroendocrine markers such as neuron-specific enolase, chromogranin A, synaptophysin, and neural cell adhesion molecule. No correlation between proliferative activity based on the Ki67 labeling index and prognosis or lymph node metastasis was found. Concerning DNA ploidy patterns, only one tumor with multiple lymph node metastases was considered to be aneuploid. In conclusion, although all of our cases were histologically classified as atypical carcinoid tumors of the thymus, most were diploid, and the patients enjoyed a relatively good prognosis.

Lipid-rich carcinoid tumor of the thymus gland: diagnosis by fine-needle aspiration biopsy

In this report we describe the cytologic features of an unusual thymic carcinoid tumor containing prominent cytoplasmic lipid vacuoles that was diagnosed by fine-needle aspiration biopsy. The tumor presented as a presternal subcutaneous mass in an 81-yr-old female, with a contiguous mediastinal mass on computed tomography. The cytomorphologic features included numerous discohesive cells with eccentric, round to oval nuclei, granular chromatin, and scant cytoplasm containing numerous intracytoplasmic, clear vacuoles. The neoplastic cells were reactive for neuroendocrine markers by immunocytochemistry and showed reactivity of the intracytoplasmic vacuoles with an oil red-O stain for neutral lipid. Ultrastructural examination confirmed the presence of intracytoplasmic lipid vacuoles and neurosecretory granules. Subsequent surgical excision confirmed the diagnosis. We believe this to be the first report describing these features in a primary thymic carcinoid tumor. The differential diagnosis of mediastinal tumors with clear-cell features and cytoplasmic vacuolization is also discussed.

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.

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.

Neuroendocrine differentiation is a common feature of thymic carcinoma

Immunohistochemical evidence of neuroendocrine differentiation in the form of reactivity for synaptophysin, neuron-specific enolase, and/or chromogranin was found in 11 of 19 (58%) thymic carcinomas having the typical morphologic features of that tumor type. Four of these 19 cases were studied ultrastructurally, and neuroendocrine-type cytoplasmic dense-core granules were found in two. In contrast, 84 thymomas were negative for these markers, except for a focal immunoreactivity for neuron-specific enolase in areas of medullary differentiation in half of the lymphocyte-rich tumors. The results of this study show that in the thymus, similar to most other organs, neuroendocrine differentiation is not limited to tumors with an identifiable neuroendocrine appearance in hematoxylin-eosin-stained slides, such as carcinoid tumor and small cell carcinoma, but rather that it represents a common event shared by the major types of malignant epithelial tumors of that organ.