Thymoma and Thymic Carcinoma Treatment (PDQ®): Treatment - Health Professional Information [NCI] - Cellular Classification of Thymoma and Thymic Carcinomas
Thymic carcinoma (also known as type C thymoma) is a thymic epithelial tumor that exhibits a definite cytologic atypia and a set of histologic features no longer specific to the thymus but rather similar to those histologic features observed in carcinomas of other organs. In contrast to type A and B thymomas, thymic carcinomas lack immature lymphocytes. Any lymphocytes that are present are mature and usually admixed with plasma cells. Hypothetically, thymic carcinoma may arise from malignant transformation of a pre-existing thymoma. This hypothetical evolution could account for the existence of thymic epithelial lesions that exhibit combined features of thymoma and thymic carcinoma within the same tumor.
Thymic carcinomas are usually advanced when diagnosed and have a higher recurrence rate and worse survival compared with thymoma.[15,16] In a retrospective study of 40 patients with thymic carcinoma, the 5-year and 10-year actuarial overall survival rates were 38% and 28%, respectively. In contrast to the thymomas, the association of thymic carcinoma and autoimmune disease is rare.
Histologic subtypes of thymic carcinoma include the following:
- Squamous cell (epidermoid) thymic carcinoma
This type of thymic carcinoma exhibits clear-cut cytologic atypia. In routinely stained sections, the keratinizing form exhibits equally clear-cut evidence of squamous differentiation in the form of intercellular bridges and/or squamous pearls, while the nonkeratinizing form lacks obvious signs of keratinization. Another subtype, basaloid carcinoma, is composed of compact lobules of tumor cells that exhibit peripheral palisading and an overall basophilic staining pattern caused by the high nucleocytoplasmic ratio and the absence of keratinization.
- Lymphoepithelioma-like thymic carcinoma
This type of thymic carcinoma has morphologic features indistinguishable from those of lymphoepithelial carcinoma of the respiratory tract. The differential diagnosis with germ cell tumors, particularly seminomas, can be difficult but important for treatment.
- Sarcomatoid thymic carcinoma (carcinosarcoma)
This is a type of thymic carcinoma in which part or all of the tumor resembles one of the types of soft tissue sarcoma.
- Clear cell thymic carcinoma
This is a type of thymic carcinoma composed predominantly or exclusively of cells with optically clear cytoplasm.
- Mucoepidermoid thymic carcinoma
This type of thymic carcinoma has an appearance similar to that of mucoepidermoid carcinoma of the major and minor salivary glands.
- Papillary thymic adenocarcinoma
This type of thymic carcinoma grows in a papillary fashion. This histology may be accompanied by psammoma body formation, which may result in a marked similarity with papillary carcinoma of the thyroid gland.
- Undifferentiated thymic carcinoma
This is a rare type of thymic carcinoma that grows in a solid undifferentiated fashion but without exhibiting sarcomatoid (spindle cell or pleomorphic) features.
Combinations of the above histologic types can occur within the same tumor. For these cases, the term, combined thymoma, can be used, followed by a listing of the components and the relative amount of each component.
- Rosai J: Histological Typing of Tumours of the Thymus. New York, NY: Springer-Verlag, 2nd ed., 1999.
- Okumura M, Ohta M, Tateyama H, et al.: The World Health Organization histologic classification system reflects the oncologic behavior of thymoma: a clinical study of 273 patients. Cancer 94 (3): 624-32, 2002.
- Chen G, Marx A, Wen-Hu C, et al.: New WHO histologic classification predicts prognosis of thymic epithelial tumors: a clinicopathologic study of 200 thymoma cases from China. Cancer 95 (2): 420-9, 2002.
- Kondo K, Yoshizawa K, Tsuyuguchi M, et al.: WHO histologic classification is a prognostic indicator in thymoma. Ann Thorac Surg 77 (4): 1183-8, 2004.
- Rena O, Papalia E, Maggi G, et al.: World Health Organization histologic classification: an independent prognostic factor in resected thymomas. Lung Cancer 50 (1): 59-66, 2005.
- Zettl A, Ströbel P, Wagner K, et al.: Recurrent genetic aberrations in thymoma and thymic carcinoma. Am J Pathol 157 (1): 257-66, 2000.
- Inoue M, Starostik P, Zettl A, et al.: Correlating genetic aberrations with World Health Organization-defined histology and stage across the spectrum of thymomas. Cancer Res 63 (13): 3708-15, 2003.
- Hirabayashi H, Fujii Y, Sakaguchi M, et al.: p16INK4, pRB, p53 and cyclin D1 expression and hypermethylation of CDKN2 gene in thymoma and thymic carcinoma. Int J Cancer 73 (5): 639-44, 1997.
- Sasaki H, Kobayashi Y, Tanahashi M, et al.: Ets-1 gene expression in patients with thymoma. Jpn J Thorac Cardiovasc Surg 50 (12): 503-7, 2002.
- Sasaki H, Yukiue H, Kobayashi Y, et al.: Cten mRNA expression is correlated with tumor progression in thymoma. Tumour Biol 24 (5): 271-4, 2003 Sep-Oct.
- Sasaki H, Ide N, Sendo F, et al.: Glycosylphosphatidyl inositol-anchored protein (GPI-80) gene expression is correlated with human thymoma stage. Cancer Sci 94 (9): 809-13, 2003.
- Penzel R, Hoegel J, Schmitz W, et al.: Clusters of chromosomal imbalances in thymic epithelial tumours are associated with the WHO classification and the staging system according to Masaoka. Int J Cancer 105 (4): 494-8, 2003.
- Suster S, Moran CA: Thymic carcinoma: spectrum of differentiation and histologic types. Pathology 30 (2): 111-22, 1998.
- Suster S, Moran CA: Primary thymic epithelial neoplasms showing combined features of thymoma and thymic carcinoma. A clinicopathologic study of 22 cases. Am J Surg Pathol 20 (12): 1469-80, 1996.
- Ogawa K, Toita T, Uno T, et al.: Treatment and prognosis of thymic carcinoma: a retrospective analysis of 40 cases. Cancer 94 (12): 3115-9, 2002.
- Blumberg D, Burt ME, Bains MS, et al.: Thymic carcinoma: current staging does not predict prognosis. J Thorac Cardiovasc Surg 115 (2): 303-8; discussion 308-9, 1998.
- Levy Y, Afek A, Sherer Y, et al.: Malignant thymoma associated with autoimmune diseases: a retrospective study and review of the literature. Semin Arthritis Rheum 28 (2): 73-9, 1998.