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

Primary thymic adenoid cystic carcinoma with high-grade transformation: A clinicopathological and immunohistochemical analysis of 4 cases

Four cases of a distinct carcinoma of the thymic gland are presented. The patients were 4 adult males with an age range from 40 to 47 years (mean, 43.5 years). Clinically, all patients presented with non-specific respiratory symptoms. None of the patients had any prior history of head and neck neoplasm or surgery in that anatomic area. Large anterior mediastinal masses were found on diagnostic imaging with concurrent metastatic disease to pleura, lungs, regional lymph nodes and bones. Microscopically, all tumors were composed of a solid proliferation of hyperchromatic, monomorphic small cells with focal cytoplasmic clearing embedded in a fibromyxoid stroma. In one case, occasional duct-like structures were identified. Immunohistochemically, the tumors were positive for pancytokeratin, CD117 and MYB and negative for myoepithelial markers. Systemic chemotherapy was initiated in all patients. Despite therapy, clinical follow-up revealed that all 4 patients died of their disease 11-23 months after their initial diagnosis. The cases in this series highlight a tumor that is different from conventional thymic carcinoma and that has the morphological and immunohistochemical features commonly seen in adenoid cystic carcinomas with high-grade transformation. Correct diagnosis is essential for patient management.

Desmoplastic Adamantinoma-like Thymic Carcinoma: Clinicopathologic, Immunohistochemical, and Molecular Study of 5 Cases

Five cases of a heretofore unreported rare variant of thymic carcinoma characterized by a striking resemblance to adamantinoma of the mandible are described. The tumors occurred in 4 women and 1 man aged 58 to 76 years (mean: 67.8 y); they arose in the anterior mediastinum and measured from 5.3 to 12.0 cm in greatest diameter (mean: 8.9 cm). Presenting symptoms included chest pain, shortness of breath, and in 2 patients, pleural effusion. One tumor was asymptomatic and discovered incidentally. Histologically, the tumors were extensively desmoplastic, and the cellular proliferation was characterized by multiple islands of squamous epithelium with striking peripheral palisading of nuclei and central areas containing clear cells resembling a stellate reticulum. Areas of preexisting spindle cell thymoma were identified in 2 cases; these areas gradually merged with the higher-grade component of the lesion. Cystic changes were noted in 3 cases. Immunohistochemical studies in 3 cases showed the tumor cells were positive for cytokeratins, p40 and p63, and all showed a high proliferation rate (>50% nuclear positivity) with Ki-67. Next-generation sequencing was performed in 2 cases that showed amplification of the AKT1 gene (copy numbers 6 and 13). Clinical follow-up in 3 patients showed recurrence and metastasis after 1 and 2 years; 1 patient passed away 2 years after diagnosis due to the tumor. Desmoplastic adamantinoma-like thymic carcinoma represents an unusual histologic variant of thymic carcinoma that needs to be distinguished from metastases from similar tumors to the mediastinum.

Unilocular thymic cyst with features of intra-thymic bronchogenic cyst: A clinicopathological correlation of 4 cases

Four cases of primary unilocular thymic with features of bronchogenic cyst are presented. The patients are three men and a woman between the ages of 43 and 57 years. All the patients presented with symptoms of cough, chest pain, and dyspnea. Diagnostic imaging revealed the presence of an anterior mediastinal cystic lesion. Initial mediastinoscopic biopsies were non-diagnostic. Surgical resection of the anterior mediastinal cystic lesion was performed in all patients. Macroscopically, all the lesions were described as large cystic lesions measuring from 2 to 4 cm in largest diameter and containing yellowish fluid. The surface of the cysts was described as corrugated and of brownish color. The walls of the cysts were not thickened and no other elements were described. Histologically, the cystic lesions were characterized by single cystic structures lined by ciliated epithelium. No atypia or mitotic activity was present in any of the cases. Immunohistochemical stains show positive staining of the respiratory epithelium with keratin and negative staining for GATA3, PAX-8, TTF-1, and Napsin. All the patients have recovered well after surgical resection.

Thymic Mucoepidermoid Carcinoma: A Clinicopathologic and Molecular Study

Thymic mucoepidermoid carcinoma (MEC) is a rare tumor, and its characteristics remain to be clarified. Here we investigated 20 cases of thymic MEC to systematically characterize its clinical, histopathologic, and molecular features. The median age of the patients was 56 years (range, 19 to 80 y), there was a slight male predilection (3:2), and 44% of the patients were asymptomatic at diagnosis. The median tumor size was 6.8 cm in diameter, 55% were pT1 tumors, and 50% were TNM stage I tumors. When 4 tumor grading systems for salivary MEC (Armed Forces Institutes of Pathology, Brandwein, modified Healey, and the Memorial Sloan-Kettering) were employed, low-grade, intermediate-grade, and high-grade tumors accounted for 35% to 70%, 5% to 25%, and 25% to 50%, respectively. Many histologic variants were noted, and 70% of the cases were classified as nonclassic variants. MAML2 rearrangement was detected in 56% of cases, and the fusion partner was CRTC1 in all cases. CRTC1-MAML2 fusion was associated with lower pT classification and lower TNM stage. The overall survival rate of all patients was 69% and 43% at 5 and 10 years, respectively. Worse overall survival was associated with higher pT stage, higher TNM stage, residual tumors, greater tumor size, high-grade tumor histology (Armed Forces Institutes of Pathology and Memorial Sloan-Kettering, but not the other 2), and with the absence of CRTC1-MAML2 fusion. Of note, none of the patients with CRTC1-MAML2 fusion-positive tumors died during the follow-up. In conclusion, the clinicopathologic and molecular findings of thymic MEC presented here are expected to contribute to the management of this rare tumor.

Thymic Carcinoma: A Review

The diagnosis of thymic carcinoma may pose significant problems not necessarily in the histopathological diagnosis but rather in assigning the thymus as specific origin. Often the tissue available for interpretation is obtained via a mediastinocopic biopsy, which raises two different issues -minimal tissue and lack of specific features to make a carcinoma of thymic origin. In addition, if to that conundrum we add that there is no magic immunohistochemical stain that will unequivocally lead to the interpretation of thymic carcinoma, then we are left with a true clinical-radiological-pathological correlation. In this review, we will highlight some of those challenges that diagnostic surgical pathologists may encounter in the histopathological assessment of thymic carcinoma as well as in the staging of these tumors.

Thymoma: Challenges and Pitfalls in Biopsy Interpretation

The interpretation of biopsy specimens in the diagnosis of thymoma is a subject that is generally not addressed in the literature. Even though the diagnosis of thymoma may seem to be an easy step in the assessment of these tumors, in reality, it is the biopsy specimen interpretation that will be use to determine course of action in any particular patient. It may determine whether a patient is a surgical candidate or on the contrary whether a patient may be benefited the most by medical therapy. In addition, there may be conditions in which all that is required is surgical resection without any further treatment, and that the evaluation of those conditions does not necessarily required the careful pathologic staging that thymomas need. In addition, it is important to highlight that in small biopsies, there are limitations not only in terms of the cellularity and other features that may not be present in such biopsy but also the limitation in term of immunohistochemical interpretation. Herein we have attempted to highlight numerous tumoral conditions that are frequently encountered in the daily practice of mediastinal pathology, some of them pose significant problems in separating them from thymomas. Needles to say, the entire spectrum of mediastinal pathology that may at any given time mimic thymoma is well beyond the scope of this review. Furthermore, we also herein emphasize the need for proper clinical and radiologic information and correlation in order to lead to a better interpretation of the biopsy specimen. The emphasis in this review is on thymoma and their possible pitfall and shortcomings while evaluating small biopsy specimens.

The Rarest of Rare Thymic Lesions: A 10-Year Surgical Pathology Experience

The thymus is a specialized primary lymphoid organ located in the midline pre-vascular mediastinum. The organ is the site of various pathological processes, neoplastic and not, whose rarity has not allowed in-depth studies on clinical or histological features of rarest and unusual variants. Herein, we report a 10-year Padova experience in the surgical pathology of the thymus, focusing on the pathological description of nonneoplastic lesions and rare epithelial and mesenchymal tumors recorded in our database, which comprises over 600 thymectomies. The extrapolated rare cases have been categorized into four groups that included 15 cysts, 18 carcinomas, 5 neuroendocrine tumors, and 2 soft tissue tumors. The cases are described from a clinical and pathological point of view and discussed in dedicated sections with a review of the most important literature. In this case, review series, we aim to update the epidemiology of these rare entities, improve diagnostic awareness, and finally, promote a collaborative network between referral centers.

Multilocular thymic cyst (MTC) and other tumors with MTC features: Pitfalls in diagnosis

Cystic lesions of the anterior mediastinum represent a well-known group of benign lesions that are relatively common in the general practice, namely in the pediatric age group. In the adult population, multilocular thymic cyst (MTC) plays an important role in occurrence as it presents as a cystic anterior mediastinal mass that clinically may mimic another anterior mediastinal tumor. In general, MTC is of rather unusual occurrence and its histopathological features have been well described in the literature. However, similar histopathological features may also be associated with a gamut of other tumoral conditions that although unrelated may be encountered growing along the walls of these cystic structures. Herein a presentation of the classical MTC and the classical histopathological features of such entity in association with other tumoral conditions will be discussed. It is highly important to underscore that the final interpretation of some of these tumors is based on a thorough evaluation of the cystic lesion and a reasonable sampling for histological evaluation so that the proper interpretation can be reached. Needless to say, the radiological and clinical information of the patients with cystic anterior mediastinal lesions is very important in the final analysis of these cases.

Mucoepidermoid carcinoma of the thymus incidentally diagnosed following two-years of non-productive cough

Mucoepidermoid carcinoma of the thymus is a rare primary thymic carcinoma. Radiologic imaging of this malignancy is rarely reported in literature. We present a patient who complained of a chronic cough for two years who was later found to have mucoepidermoid carcinoma of the thymus. Chest radiograph revealed a large anterior mediastinal mass. Follow-up computed tomography of the thorax demonstrated a large, heterogeneous anterior mediastinal mass with traversing vessels. F-18 fluorodeoxyglucose positron emission tomography-computed tomography demonstrated high avidity in the lesion with areas of diminished activity thought to represent necrosis. Following surgical resection, pathology revealed high-grade mucoepidermoid carcinoma of the thymus extending into the skeletal muscle and pericardium with evidence of lymphovascular invasion. The patient received external beam radiation therapy and has remained disease-free for three years.

Micronodular Thymomas With Prominent Cystic Changes: A Clinicopathological and Immunohistochemical Study of 25 Cases

Twenty-five cases of micronodular thymomas with prominent cystic changes are presented. The patients are 13 men and 12 women between the ages of 38 and 69 years. Clinically, the majority of patients presented with nonspecific symptoms of cough, chest pain, and dyspnea. Four patients were asymptomatic. Diagnostic imaging showed the presence of an anterior mediastinal mass and surgical resection of the tumor mass was performed in all the patients. Histologically, all the tumors were characterized by the presence of cystic structures of varying sizes lined by different types of epithelium. In addition, the tumors were characterized by nodules of epithelial cells embedded in a lymphocyte-rich stroma with germinal centers. Twenty-one tumors were encapsulated while 4 tumors were minimally invasive. Immunohistochemical stains were positive for keratin in the nodular epithelial component while CD45 and CD20 were positive in the lymphoid component. Clinical follow-up ranging from 12 to 24 months was obtained in 19 patients. All the patients were alive and well without disease. No clinical follow-up was available in 6 patients. The cases presented in this article highlight the existence of cystic micronodular thymomas, which can be easily misdiagnosed as a multilocular thymic cyst.

Thymic Mucoepidermoid Carcinoma: A Systematic Review and Meta-analysis

Thymic mucoepidermoid carcinoma is a rare tumor that remains poorly characterized and a diagnostic challenge. The aim of this review is to characterize this tumor in a larger cohort of patients using all the available cases in the literature. We systematically searched the PubMed and Scopus database for primary thymic mucoepidermoid carcinoma. A total of 24 studies were included in the final analysis. A total of 41 patients were identified; 23 (56.1%) were male and 18 (43.9%) were female. Mean age was 49.8±21.3 years. Mean tumor size was 7.6±3.5 cm. Twenty (66.7%) were low grade and 8 (26.7%) were high grade. In total, 20 (55.6%) patients were treated with surgery alone. Nodal dissection was performed in 4 cases only. Two patients had MAML2 gene rearrangement and 2 were negative. Follow-up time varied from 2 to 93 months. A total of 13 (44.8%) patients died of disease with a median survival of 12 months. There seems to be a bimodal age distribution with peaks between second and third decades of life, and between sixth and eight decades. Lymph node sampling is frequently not performed; however, we recommend performing it, as it may lead to more accurate staging. There is limited data regarding the utility of MAML2 gene rearrangement in the thymic location. Histologic grade and tumor stage/resectability are the main prognostic factors.

Cystic and Encapsulated Atypical Thymoma (World Health Organization Type B3)

OBJECTIVES

Eight cases of encapsulated and cystic atypical thymomas (World Health Organization type B3) are presented.

METHODS

Cases were identified after review of more than 500 thymomas. Histologic material from surgical resections was evaluated.

RESULTS

The patients are seven men and one woman aged 43 to 71 years. Seven patients presented with nonspecific symptoms while one mass was found on autopsy. The tumors were 4 to 6 cm in greatest dimension and showed prominent cystic changes with an epithelial proliferation arranged in sheets and cords. Increased mitotic activity and nuclear pleomorphism were not identified. All tumors were encapsulated. Immunohistochemical studies showed the tumor cells positive for keratin cocktail, keratin 5/6, and p63. Clinical follow-up was available in five patients. All were alive without recurrence.

CONCLUSIONS

These cases represent an unusual variant of atypical thymoma that can be misdiagnosed as thymic carcinoma or multilocular thymic cyst. Awareness of this histologic growth pattern is important for accurate diagnosis.

Thymoma and thymic carcinoma associated with multilocular thymic cyst: a clinicopathologic analysis of 18 cases

Background

Multilocular thymic cysts (MTCs) associated with thymomas or thymic carcinomas (TCs) are rare and may be misdiagnosed as other benign cystic lesions.

Methods

We retrospectively analysed 18 cases of thymomas or TCs associated with MTCs, which were retrieved from 309 consecutive patients with thymomas or TCs in the Chinese population, emphasizing clinicopathologic characteristics, immunophenotypes and the prognostic impact.

Results

A total of 14 tumours were described as cystic or solid-cystic masses, and the other 4 tumours were described as solid masses. Histologically, 2 atypical type A, 2 type AB, 1 type B1, 8 type B2, 1 type B3, 1 microscopic thymoma (type A), 2 squamous cell carcinomas (SCCs) and 1 lymphoepithelioma-like carcinoma (LELC) were classified. Prominent multilocular cystic areas with chronic inflammation were observed. The follow-up ranged from 2 to 79 months. Sixteen patients survived without any evidence of recurrence after complete resection.

Conclusions

Our study suggests that thymomas or TCs associated with MTCs are rare in the Chinese population and have a better clinical behaviour than thymomas or TCs without MTCs. Our data also expand the histologic spectrum of thymomas or TCs accompanied by MTC. To our knowledge, this is the first report of atypical type A thymoma and LELC associated with MTCs.

Primary Salivary Gland Type Tumors of the Thymus

The existence of primary salivary gland type tumors (SGTs), similar to those occurring in the major salivary glands, is well known in the thoracic cavity. When they occur in this anatomic area, these tumors more commonly arise from the lung. However, the existence of these tumors primarily affecting the thymus, although recognized in the literature, is rather not well documented or known. In addition, contrary to the primary lung SGTs, which are predominantly of the malignant type, these tumors when occur in thymus encompass a wider spectrum of biology ranging from benign to low grade, and high grade malignancy. The recognition of SGTs in the thymus, even though rare, is important to properly address treatment and prognosis. Herein, we will discuss the numerous benign a malignant SGTs that have been described in the thymus and highlight the difficulty that these tumors may pose when occurring in the thymic area.

Pleuromediastinal Epithelial-Myoepithelial Carcinomas: A Clinicopathologic and Immunohistochemical Study of Two Cases

OBJECTIVES

Two cases of epithelial-myoepithelial carcinoma are presented, one arising in the pleura and the other in the anterior mediastinum. The cases represent a unique distribution of these tumors within the thoracic cavity.

METHODS

Both patients were men aged 25 and 68 years, respectively, who had chest pain and dyspnea. Imaging revealed an anterior mediastinal mass in one patient and a pleural-based tumor in the other. Neither patient had any history of malignancy, and physical examination did not disclose any tumor elsewhere.

RESULTS

Initial biopsy specimens were inconclusive, and final diagnosis was deferred to surgical resection performed via median sternotomy and thoracotomy, respectively. Histologically, the lesions were characterized by epithelial and myoepithelial elements distributed as discrete tubules or duct-like structures or sheets of neoplastic cells. Immunohistochemistry showed positive staining for cytokeratin and epithelial membrane antigen in the epithelial component, while S100 protein and smooth muscle actin were expressed in the myoepithelial elements. Follow-up showed that both patients were alive 6 and 12 months after surgery, respectively.

CONCLUSIONS

These cases highlight the ubiquitous distribution of salivary gland-type tumors in the thoracic cavity. These tumors should be included in the differential diagnosis of thoracic neoplasms also in locations other than the lung.

Thymomas With Extensive Clear Cell Component: A Clinicopathologic and Immunohistochemical Study of Nine Cases

OBJECTIVES

Nine cases of thymomas with an extensive clear cell component are presented.

METHODS

The patients were six men and three women aged between 45 and 62 years (mean, 52 years). Presenting symptoms included shortness of breath, chest pain, and cough. Diagnostic imaging revealed anterior mediastinal masses in all patients, and all underwent thymectomy.

RESULTS

Grossly, the tumors varied from 3 to 9 cm in the greatest dimension. Four cases were invasive and five encapsulated. Histologically, the tumors were characterized by an epithelial cell component with extensive clear cell change, admixed with lymphocytes in varying proportions. Immunohistochemically, the tumors demonstrated the typical immunophenotype of thymomas characterized by positive staining of the epithelial cells for pancytokeratin and cytokeratin 5/6, absent expression of CD5 and c-kit, and reactivity of the lymphocytes for terminal deoxynucleotidyl transferase. Clinical follow-up available for six patients showed that all were alive and well 12 to 24 months after surgical resection.

CONCLUSIONS

The cases herein presented highlight an unusual feature in thymoma that has more commonly been ascribed to thymic carcinoma. They also emphasize the importance of correct diagnosis to determine the appropriate treatment strategy and to accurately predict prognosis.

Analysis of MAML2 rearrangement in mucoepidermoid carcinoma of the thymus

Primary thymic mucoepidermoid carcinoma (TMEC) is rare. High-grade TMEC can be difficult to distinguish from poorly differentiated squamous cell carcinoma and adenosquamous carcinoma. A strong association between mucoepidermoid carcinoma (MEC) and t(11;19)(q21;p13) has been observed in other anatomical sites. Although this translocation is largely considered a disease-defining event for MEC, its incidence in TMEC has not been explored. In this study, we evaluate the value of identifying MAML2 rearrangement by fluorescence in situ hybridization (FISH) to distinguish TMEC from poorly differentiated squamous cell carcinoma and adenosquamous carcinoma. Cases of TMEC, moderate to poorly differentiated squamous cell carcinoma, and adenosquamous carcinoma were re-reviewed by 3 surgical pathologists and classified according to the current World Health Organization classification of thymic tumors (2004). Cases of TMEC were histologically graded using the Brandwein system. FISH was used to detect MAML2 rearrangements using a break-apart probe. FISH for MAML2 rearrangement was performed on cases of TMEC (n = 2), thymic squamous cell carcinoma (n = 5), and thymic adenosquamous carcinoma (n = 3). The 2 cases of TMEC showed MAML2 rearrangement. All other tested cases did not show rearrangement of MAML2. In conclusion, using FISH to identify MAML2 rearrangement is a valuable diagnostic tool in the evaluation of thymic malignancies, specifically, distinguishing TMEC from squamous cell carcinoma and adenosquamous carcinoma. These findings also suggest that TMEC has both histomorphologic and cytogenetic similarities to cases of MEC arising from other anatomical sites.

Thymic carcinoma, part 1: a clinicopathologic and immunohistochemical study of 65 cases

The clinicopathologic and immunohistochemical features of 65 primary thymic carcinomas are reported (43 men and 22 women; 19-81 years old). Thymectomy was performed in all cases. Masaoka staging for 53 patients showed 3 patients in stage I, 14 in stage II, 17 in stage III, and 19 in stage IV. Histologic studies revealed 9 carcinoma subtypes. Immunohistochemically, the tumors showed high rates of expression for cytokeratin, Pax8, and FoxN1. Follow-up for 62 patients revealed that 36 patients were alive (mean follow-up, 51.1 months) and 26 had died (mean survival, 47.5 months). The 3- and 5-year overall survival rates were 76.6% and 65.7%, respectively. Our findings suggest that thymic carcinomas may behave less aggressively than commonly believed. Lymph node status and tumor size seem to be important prognostic factors. The Masaoka staging system does not seem to reliably predict outcome.

Primary MALT-type lymphoma of the thymus: a clinicopathological and immunohistochemical study of six cases

BACKGROUND

Six cases of primary extranodal marginal zone B-cell lymphoma of the thymus (MALT [mucosa-associated lymphoid tissue]) are described.

METHODS

The patients were all women between 48 and 59 years. Clinically, all patients, except for one, were Caucasians. Two patients had a history of autoimmune disease, while one was being investigated for such a possibility. The remaining three patients did not have a history of autoimmune disorders.

RESULTS

In those patients who had symptoms related to their anterior mediastinal masses, nonspecific symptoms, including shortness of breath and chest pain, predominated. Histologically, the tumors had the classical morphologic features of cystic and solid areas with an atypical monocytoid cellular proliferation. Immunohistochemical stains performed in all cases showed kappa monotypic expression and B-cell phenotype.

CONCLUSIONS

The current cases highlight that MALT lymphomas of the thymus can occur in a setting not related to autoimmune disease or in those not of Oriental ethnic background and that mediastinal cystic lesions require proper sampling in order to adequately evaluate the possibility of MALT lymphoma.

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.

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.

Mucoepidermoid carcinoma of the thymus

Mucoepidermoid carcinoma of the thymus is a rare carcinoma and there is little agreement about the treatment of this tumor. According to the analysis of previously reported tumors, biologic behavior of the tumor correlated with the spread of the lesion and degree of differentiation. We report a case of this tumor in a 31-year-old man. Resection of the tumor included the left upper lobe of the lung, the phrenic nerve, pericardium and disseminations in the pleura. The clinicopathological feature of this case was high-stage disease and low-grade histology. Postoperative chemotherapy and radiotherapy were performed, and the patient is alive without recurrence 14 months after surgery.

Low-Grade Serous Carcinoma of the Ovary Metastatic to the Anterior Mediastinum Simulating Multilocular Thymic Cysts

Three cases of serous borderline tumors of the ovary with areas of serous low-grade carcinoma metastatic to the anterior mediastinum simulating multilocular thymic cysts are presented. The patients are women between the ages of 33 and 50 years. The 3 women had a prior history of primary ovarian neoplasms diagnosed over a period ranging from 3 to 20 years; the 3 patients were in stages IIIA, IIIB, and III. Follow-up radiologic examination revealed the presence of an anterior mediastinal tumor. The 3 patients underwent surgical resection of the mediastinal tumor. Grossly, the mediastinal tumors measured from 7 to 9 cm in greatest diameter and were described as cystic with solid areas. Focal areas of hemorrhage were present, but frank necrosis was not identified. Histologically, all the tumors basically showed similar histopathologic features, namely, those described in multilocular thymic cysts, ie, cystic structures lined by either squamous or low cuboidal epithelium, lymphoid hyperplasia, cholesterol cleft granulomas, and remnants of thymic tissue. In addition, within the cystic structures, there was a neoplastic cellular proliferation with papillary architecture, nuclear atypia, and scattered mitotic figures. Immunohistochemical studies for keratin, MOC31, and CA-125 showed positive staining in tumor cells while placental-like alkaline phosphatase was negative. Two patients remain alive and well after follow-up ranging from 6 to 18 months and 1 patient died of tumor 18 years after initial diagnosis.

Mucoepidermoid carcinoma of the thymus: a case presentation and a literature review

Mucoepidermoid carcinoma of the thymus is an unusual, but well-recognized variant of thymic malignant tumors. Its biologic behavior generally depends on the degree of differentiation and the amount of cellular atypia. High grade tumors can be aggressive neoplasms with a tendency to invade and develop metastases. We report on a case of a 53-year-old man, who presented chest discomfort, dyspnea, and weakness. As heart function tests were normal, the patient underwent radiologic examination, which showed a well-demarcated mass in the anterior mediastinum. Histologic examination of the surgically resected mass showed features of a mucoepidermoid carcinoma with associated infiltration of the pleural tissue. Postoperative radiotherapy and chemotherapy were performed, and the patient died two months after initial diagnosis. In case of the absence of metastatic disease or other common primary neoplasms of the thymus, the diagnosis of a mucoepidermoid thymic carcinoma should be taken into consideration, although this tumor is rare.

Thymic carcinoma: a clinicopathological and immunohistological study of 19 cases

AIMS

To study 19 cases of primary thymic carcinoma in order to define the clinicopathological features and the precise histochemical profile of this rare and heterogeneous group of tumours of the anterior mediastinum.

METHODS AND RESULTS

The study group consisted of 13 males and six females, with a mean age of 58.5 years (range 29-75 years). Superior vena cava syndrome and chest pain were the main presenting symptoms. Three patients were asymptomatic. No patient had myasthenia gravis. Six different histological types were identified: neuroendocrine tumours (six patients), epidermoid carcinoma (five patients), sarcomatoid carcinoma (three patients), lymphoepithelioma-like carcinoma (two patients), mucoepidermoid carcinoma, clear cell carcinoma, and undifferentiated carcinoma (one patient each). The clear cell carcinoma was associated with a thymic cyst. No association with thymoma was observed. Surgical resection, performed in 10 cases, was complete in two. Sixteen patients received thoracic radiation, and 11 received systemic chemotherapy. Follow-up information was available in 16 cases; 12 patients presented with local or metastatic relapse, and 10 patients died of their tumour. The overall 5-year survival was 14.5%.

CONCLUSION

Primary thymic carcinoma is a very heterogeneous group of tumours of the anterior mediastinum with an aggressive clinical behaviour, and a poor overall prognosis.

Thymic Mucoepidermoid Carcinomas

BACKGROUND

Primary thymic carcinomas are rare malignant neoplasms, of which at least 10 different histologic variants have been described. Among these variants, thymic mucoepidermoid carcinomas morphologically similar to the homonymous salivary gland counterparts are particularly unusual; only 9 cases for which clinicopathologic features were available have been reported.

OBJECTIVE

To study the clinicopathologic features of primary thymic mucoepidermoid carcinoma in an effort to better define their histologic features and biologic behavior.

DESIGN

The clinical and pathologic features of 10 cases of thymic mucoepidermoid carcinoma were reviewed and compared with those of previously reported cases.

RESULTS

The patients ranged in age from 8 to 84 years (mean 49 years), with 6 men and 4 women. The initial manifestations included respiratory symptoms and weight loss. Some patients were asymptomatic. All tumors were located adjacent to residual benign thymic tissue, and 3 cases were associated with multilocular thymic cysts. Histologically, the tumors consisted of sheets, lobules and nests of squamous, mucinous and intermediate cells in densely fibrotic stroma. There were 8 low-grade cases and 2 high-grade cases. The 2 patients with high-grade tumors died 1 year after diagnosis, whereas all but 1 patient with low-grade tumors in which follow-up was available were found to be alive and well on follow-up examination. One patient with low-grade tumor but high-stage disease died after developing a local recurrence. Among the 9 cases reported in the literature, 4 cases resulted in fatal outcomes; 2 cases were high-stage disease and 2 were high-grade tumors.

CONCLUSIONS

Thymic mucoepidermoid carcinomas are predominantly low-grade tumors, and may be associated with multilocular thymic cysts. Poor prognosis is related to high-grade histology and high-stage disease.

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.

Mucoepidermoid carcinoma of the thymus: a case report

Mucoepidermoid carcinoma of the thymus is an extremely rare malignant mediastinal neoplasm, and to our knowledge, only 13 cases have been reported. We report a case of mucoepidermoid carcinoma of the thymus that was seen in a 53-yr-old man with right chest pain. Chest CT scan showed a huge, cystic mass having a focal solid portion with direct invasion of the adjacent anterior chest wall and pericardium in the anterior mediastinum. Mucoepidermoid carcinoma of the thymus should be included in the differential diagnosis for masses of the anterior mediastinum associated with extensive cystic changes, although the carcinoma is exceedingly rare.

Cystic Adenomatoid Tumor of the Mediastinum

A case of adenomatoid tumor presenting as a mass in the anterior mediastinum is described. The patient was a 56-year-old woman with left side chest wall pain who showed a mediastinal mass on chest x-ray and CT scans. Thorough clinical and radiographic examination did not reveal any evidence of tumor elsewhere. At surgery, the tumor was found adjacent to the anterior pericardial reflection. Grossly, the tumor measured 5.5 x 5.5 x 3 cm and showed a homogeneous cut surface with numerous cystic structures that varied from 0.5 to 1.5 cm in greatest diameter. Histologic examination showed numerous cystic spaces lined by flattened or cuboidal epithelial cells. The walls of the cysts showed a proliferation of small canalicular structures lined by round to polygonal epithelioid cells with vacuolated eosinophilic cytoplasm. Immunohistochemical studies showed strong positivity of the epithelioid cells for AE1/AE3 cytokeratin, CK5/CK6, and calretinin. Stains for CK7, CK20, alpha-fetoprotein, CD31, carcinoembryonic antigen, MOC 31, and chromogranin were negative. Electron microscopic examination showed numerous long microvilli on the cell surface and abundant tonofilaments/desmosomal plaques in the tumor cells, characteristic of mesothelial cells. The patient is alive and well and free of recurrence 1 year following surgery. Adenomatoid tumor is a rare neoplasm that should be added in the differential diagnosis of anterior mediastinal masses. Immunohistochemical and ultrastructural studies may be of aid in identifying the characteristic features of mesothelial cells and to avoid mistaking this lesion for more ominous conditions.

Utility of immunohistochemistry in separating thymic neoplasms from germ cell tumors and metastatic lung cancer involving the anterior mediastinum

A variety of primary and metastatic neoplasms can involve the anterior mediastinum and have similar radiographic or histologic appearances. We report an immunohistochemical (IHC) panel that includes CD5, placental-like alkaline phosphatase (PLAP), thyroid transcription factor 1 (TTF-1), cytokeratin (CK) 7, CK20, CK5/6, and CD57 for the separation of thymic neoplasms from germ cell tumors (GCTs) and metastatic lung malignancies. One hundred cases representing different types of neoplasms involving the anterior mediastinum were retrieved and consisted of 20 pulmonary adenocarcinomas (PAs), 20 pulmonary large cell carcinomas (PLCs), 20 pulmonary squamous cell carcinomas (PSCCs), 20 thymomas (Ths), 10 invasive thymomas (IThs), and 10 thymic carcinomas (TCs). Fifteen cases of GCTs were also included in the study. CD5 was positive in 17 of 20 PAs, 11 of 20 PLCs, 2 of 15 GCTs, and 9 of 10 TCs. PLAP was positive in 5 of 20 PAs, 2 of 20 PLCs, 1 of 20 PSCCs, and 11 of 15 GCTs. TTF-1 was positive in 18 of 20 PAs, 10 of 20 PLCs, and 2 of 20 PSCCs. CK7 was positive in 20 of 20 PAs, 15 of 20 PLCs, 8 of 20 PSCCs, 5 of 15 GCTs, 11 of 20 Ths, 7 of 10 IThs, and 4 of 10 TCs. CK20 was positive only in 2 of 20 PAs. CK5/6 was positive in all cases of PSCC, Th, ITh, and TC, in 9 of 20 PLCs, and 1 of 15 GCTs. CD57 was positive in 9 of 20 PAs, 3 of 20 PLCs, 8 of 15 GCTs, 13 of 20 Ths, and 6 of 10 IThs. In conclusion, CD5 had low specificity for TC (60%) because it also stained 85% of PA and 55% of PLC. CK5/6 was a sensitive but not a specific IHC marker for the epithelial component of thymic neoplasms (100%); TTF-1 had a good sensitivity (90%) and excellent specificity (100%) for distinguishing PA from thymic neoplasms. An IHC panel consisting of CD5, CK5/6, PLAP, TTF-1, and CD57 is useful for the separation of thymic neoplasms from other epithelial malignancies involving the mediastinum.

Primary high-grade mucoepidermoid carcinoma of the minor salivary glands with cutaneous metastases at diagnosis

Mucoepidermoid carcinoma (MEC) represents 15% of all salivary glands malignancies. Metastatic disease at diagnosis is observed in less than 5% of the cases. The lung is the most commonly involved site. This is the first reported case of high-grade MEC of the salivary gland with skin metastases at diagnosis. This feature was associated with a chemoresistant and aggressive behaviour. Differential diagnosis between metastatic MEC and primary skin MEC is essential for therapeutic management and prognosis.

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.

Thymic carcinomas, but not thymomas and carcinomas of other sites, show CD5 immunoreactivity

Thus far, there are no immunohistochemical markers that are specific for thymic epithelial neoplasms, although demonstration of immature T cells in an epithelial tumor can indirectly support a diagnosis of thymoma. In this study, the usefulness of a paraffin section-reactive CD5 antibody (clone CD5/54/B4) for supporting the thymic origin of an epithelial neoplasm was evaluated. Antigen retrieval was effected by microwaving in citrate buffer. Sixteen of 24 thymic carcinomas (67%) were immunoreactive for CD5, including nine of nine squamous cell, two of two undifferentiated, two of four lymphoepithelioma-like, and one case each of basolid carcinoma, clear cell carcinoma, and unclassified thymic carcinoma, but none of four thymic small cell carcinomas. None of 17 cases of benign thymoma and 21 cases of invasive thymoma (including six cases classifiable as well-differentiated thymic carcinoma using the Muller-Hermelink criteria) was immunoreactive for CD5, in the presence of CD5-positive lymphocytes as an internal positive control. Two of three thymic neoplasms with features borderline between thymic carcinoma and invasive thymoma were immunoreactive for CD5. In contrast, none of 61 cases of other malignant neoplasms with a tendency to involve the mediastinum was immunoreactive for CD5, including 40 nonthymic carcinomas and 13 malignant germ cell neoplasma. CD5 staining of thymic epithelial tumors correlated with the absence of tumor-associated CD99-positive thymocytes, as demonstrated in our previous studies. We conclude that CD5 is a useful marker of primary thymic carcinomas. Taken together, CD5 and CD99 (or other immature T-cell markers such as TdT and Cd1a) should be particularly useful in evaluating mediastinal and other biopsy samples of possible thymic epithelial neoplasms and in the subtyping of these tumors.

A case of sarcomatoid carcinoma of the thymus

A 57-year-old woman presented with a 10 x 10 cm anterior mediastinal mass. The tumor had invaded the pericardium, both lungs and the left brachiocephalic vein, and was treated by partial resection and postoperative radiation therapy. Pathological examination of the tumor revealed squamous cell carcinoma with a spindle cell sarcomatous component. Immunohistochemically, keratin and epithelial membrane antigen were positive in both the spindle cell sarcomatous areas and the squamous cell carcinomatous area and thus, a diagnosis of thymic carcinoma of sarcomatoid type was made. The patient died of recurrent disease 1 year after surgery. This case is the seventh reported in the English literature. Because of the poor outcome, adjuvant therapy is recommended.