Cystic well-differentiated squamous cell carcinoma of the thymus: a clinicopathological and immunohistochemical study of six cases

Basaloid Squamous Cell Carcinomas of the Thymus With Prominent B-Cell Lymphoid Hyperplasia: A Clinicopathologic and Immunohistochemical Study of 10 Cases

Ten cases of basaloid squamous cell carcinomas of the thymus are presented. The patients are 6 women and 4 men ranging in ages between 51 and 72 years (average: 61.5 y), who presented with nonspecific symptoms of cough, dyspnea, and chest pain with no history of malignancy, myasthenia gravis, or other autoimmune disease. Surgical resection of the mediastinal masses via thoracotomy or sternotomy was performed in all patients. Grossly, the tumors varied in size from 2 to 8 cm, were light tan in color, solid and slightly hemorrhagic, and had infiltrative borders. Histologically, scanning magnification showed elongated interanastomosing ribbons of tumors cells embedded in a lymphoid stroma containing germinal centers. At higher magnification, the tumors cells were round to oval with moderate amounts of lightly eosinophilic cytoplasm, oval nuclei, moderate cellular atypia, and mitotic activity ranging from 3 to 5 mitotic figures per 10 HPFs. In 8 cases, the tumor invaded perithymic adipose tissue, in 1 case the tumor infiltrated pericardium, and in 1 case, the tumor involved the pleura. Immunohistochemical stains showed positive staining in the epithelial component for pancytokeratin, p63, keratin 5/6, and p40, while CD20 and CD79a characterized the lymphoid component. Clinical follow-up was obtained in 7 patients. Two patients died within 24 months and 5 patients remained alive between 12 and 60 months. The current cases highlight the unusual feature of B-cell lymphoid hyperplasia in these tumors and their potential aggressive behavior.

Thymic squamous cell carcinoma lurking in a growing large cyst A case report

An 81-year-old man was admitted for resection of an asymptomatic left anterior mediastinal tumor. Chest computed tomography showed that a small, homogeneous lesion had grown to a large, cystic lesion (80 mm) over a 5-year period. The cystic tumor was removed with adherent structures such as the left upper pulmonary parenchyma and lower part of the left innominate vein via median sternotomy with assistance from a left thoracoscopic procedure. Macroscopically, a solid tumor was located within the large multilocular cyst. The pathological diagnosis was cystic squamous cell carcinoma (12 mm), which had not infiltrated any surrounding organs. The patient has remained well without recurrence as of 4 years postoperatively.

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.

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.

Thymic Squamous Cell Carcinoma: A Population-Based Surveillance, Epidemiology, and End Result Analysis

Objectives

Thymic squamous cell carcinoma (TSCC) is a rare neoplasm that has been sparsely cited in the literature. The aim of this study was to determine disease characteristics and prognostic factors of patients in a Surveillance, Epidemiology, and End Results (SEER) analysis.

Methods

Cases from 1990-2016 were retrieved from the SEER database and demographics, treatments, and survival outcomes were analyzed.

Results

The TSCC accounted for 72.4% of the thymic carcinomas and 7.2% of thymic tumors. The 276 patients (165 men) selected for analysis had a median age of 65 (24-85) years, and 201 patients were diagnosed with Masaoka-Koga stage III/IV. The median survival of TSCC was 59 months with a 49.0% 5-year OS rate, a better prognosis than lymphoepithelioma-like carcinoma (32.1%) and undifferentiated carcinoma (33.3%). Multivariate analysis revealed the Masaoka-Koga stage (p = 0.003) and surgical types (complete resection, incomplete resection, and none; p < 0.001) were determinants of survival. Complete resection had the best prognosis with a 72.7% 5-year OS rate. Chemotherapy was an independent protective factor (HR = 0.555, 95% CI 0.347-0.886; p = 0.014) though poor survival was showed in univariate analysis. And the survival benefit of chemotherapy was validated in PSM analysis (3-year OS rate was 77.7% with chemotherapy vs. 52.8% without chemotherapy; p = 0.014).

Conclusions

TSCC was frequently diagnosed in older patients with advanced Masaoka-Koga stage and had more favorable survival than other subtypes of thymic carcinomas. Complete resection is the preferred treatment. Masaoka-Koga stage and chemotherapy had a strong association with prognosis.

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.

Non-Neoplastic and Benign Tumoral Lesions of the Thymic Gland: A Review and Update

The thymus is a dynamic organ that undergoes changes throughout life and can demonstrate a myriad of pathologic alterations. A number of benign entities of the thymus prove to be diagnostic dilemmas owing to their resemblance and association with true thymic tumors. These are usually discovered incidentally on routine imaging and most patients are either asymptomatic or present with signs and symptoms of compression of adjacent organs. The radiologic appearance of these lesions varies from simple cysts to complex masses that are suspicious for malignancy. The diagnosis is usually made purely on morphologic grounds, however, immunohistochemical stains can help rule out possible differential diagnoses. Surgical removal is usually curative in these lesions and recurrences are rare. The prognosis is excellent, however, some of these lesions may be associated with myasthenia gravis and/or thymomas. In this review, we describe non-neoplastic lesions and benign tumoral lesions of the thymus, with emphasis on the clinical, radiologic, and pathologic features. The differential diagnosis of each entity is also discussed.

[Thymic carcinomas]

Thymic carcinomas (TC) are approximately 10 times less prevalent than thymomas but of high clinical relevance because they are more aggressive, less frequently resectable than thymomas and usually refractory to classical and targeted long-term treatment approaches. Furthermore, in children and adolescents TC are more frequent than thymomas and particularly in this age group, germ cell tumors need to be a differential diagnostic consideration. In diagnostic terms pathologists face two challenges: a), the distinction between thymic carcinomas and thymomas with a similar appearance and b), the distinction between TC and histologically similar metastases and tumor extensions from other primary tumors. Overcoming these diagnostic challenges is the focus of the new WHO classification of thymic epithelial tumors. The objectives of this review are to highlight novel aspects of the WHO classification of thymic carcinomas and to address therapeutically relevant diagnostic pitfalls.

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.