Thymic carcinoma pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Marjan Khan M.B.B.S.[2]

The thymic carcinoma is a tumor of the thymic epithelium, but it is associated with a lack of immature lymphocytes and often presents with a more invasive or metastatic disease.^[1] The pathophysiology of thymic carcinoma depends on the histological subtype. On microscopic histopathological analysis, thymic carcinoma is divided into squamous cell carcinoma, basaloid carcinoma, mucoepidermoid carcinoma, lymphoepithelioma-like carcinoma, sarcomatoid carcinoma (carcinosarcoma), clear cell carcinoma, papillary adenocarcinoma, carcinoma with t(15;19) translocation, neuroendrocrine carcinomas, undifferentiated carcinoma, and combined thymic epithelial tumors.^[2] Thymic carcinoma has not been reported in association with myasthenia gravis, in contrast with thymoma^[3]

• The thymic carcinoma is a tumor of the thymic epithelium, but it is associated with a lack of immature lymphocytes and often presents with a more invasive or metastatic disease.^[1]
• In contrast to thymoma, thymic carcinoma has not been reported in association with myasthenia gravis.

• Development of thymic carcinoma is the result of multiple genetic mutations.^[3]
• Genetic mutations involved in the pathogenesis of thymic carcinoma include:

• Gain of chromosome 1q, 17q, and 18
• Deletion of chromosome 3p, 6, 13q, 16q, and 17p

• Paraneoplasic syndromes has been reported among patients with thymic cancer (neuroendocrine subtype), however the syndrome is not as common as with thymoma patients.

On microscopic histopathological analysis, characteristic findings of thymic carcinoma are:

• Cytologically malignant – variable morphology
• +/-Squamous differentiation

• CD5 +ve (90% of cases)
• CD117 +ve (87% of cases)
• CD7 +ve
• TTF-1 -ve