Thymic carcinoma classification
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [2]
Overview
Thymic carcinomas are categorized in low and high grade histological subtypes, which includes 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.
Classification
- Squamous cell carcinoma: This subtype of thymic carcinoma is the most common and exhibits atypia with a clear-cut aspect of keratinization with keratin pearls as seen in squamous cell carcinomas. Squamous cell carcinoma lack of capsule and presents with necrosis and hemorrhage.
- Basaloid carcinoma: This subtype consists solid lobules of tumor cells with marginal palisading, without keratinization and a basophilic pattern due to an elevated nucleocytoplasmic ratio.
- Mucoepidermoid carcinoma: The characteristic features for this rare subtype is the presence of squamous and mucus producing cells, with moderate atypia. It has a mucinous macroscopic appearance.
- Lymphoepithelioma-like carcinoma: The morphology of this subtype resembles the nasopharingeal lymphoepitelioma, with syncytial growth of undifferentiated malignant cells.
- Sarcomatoid carcinoma (carcinosarcoma): It is also known as spindle cell thymic carcinoma, is an infiltrative neoplasm with large areas of coagulative necrosis and without a capsule. It is an uncommon tumor that affects patients between 40-80 years old.
- Clear cell carcinoma: Consist of cells with minimal nuclear atypia with a characteristic lucent cytoplasm and a lobulated architecture without sinusoidal vasculature (in contrast with the renal clear cell carcinoma)
- Papillary adenocarcinoma: It has a tubulopapillary pattern growth with cuboidal cells and Psammoma bodies may be present. Type A thymoma may be the origin of this subtype of carcinoma due an expression of malignant transformation.
- Carcinoma with t(15;19) translocation: It is an aggressive tumor with a translocation t(15;19)(q13:p13.1 )that has the characteristic presence of undifferentiated cells with high mitotic activity and squamous morphology.
- Neuroendocrine Carcinomas: The neuroendocrine thymic carcinomas are classified in 4 categories: typical, atypical, small cell and large cell carcinomas. The typical and atypical are categorized as well differentiated neuroendocrine carcinomas, and the small cell and large cell carcinomas are categorized as poor differentiated.