Immunohistochemical KIT (CD117) expression in thymic epithelial tumors
ABSTRACT It is sometimes very difficult both clinically and pathologically to distinguish thymic epithelial tumors from primary lung carcinoma with massive anterior mediastinal involvement. The expression of KIT (CD117) in thymic epithelial tumors was investigated in order to evaluate its usefulness as a marker supporting differential diagnosis and choice of therapy.
We examined the immunohistochemical expression of KIT in 70 resected thymic epithelial tumors (thymomas, 50; thymic carcinomas, 20) that had been reclassified on the basis of the World Health Organization histologic classification system. We also compared the expression of KIT and CD5 in 20 thymic carcinomas with their expression in 20 resected pulmonary squamous cell carcinomas that were spreading directly into the mediastinum.
Of the 50 thymomas, only 2 (4%) showed positive immunoreactivity for KIT (type A thymoma, 1; type B3 thymoma, 1), whereas 16 of the 20 thymic carcinomas (80%) showed positive immunoreactivity. Testing was positive for CD5 in 14 of the 20 thymic carcinomas (70%). In the pulmonary squamous cell carcinomas, in contrast, the immunohistochemical expression of KIT and CD5 was found in only 4 of 20 carcinomas (20%) and 3 of 20 carcinomas (15%), respectively. Furthermore, of the 40 specimens examined (either thymic or lung carcinoma) all 13 that were positive for both KIT and CD5 were thymic carcinomas, and 13 of the 16 that were negative for both were lung carcinomas.
KIT expression is a useful immunohistochemical marker for the diagnosis of thymic carcinoma, and its examination in combination with CD5 immunohistochemistry would greatly help in the differential diagnosis of primary thymic carcinoma from pulmonary squamous cell carcinoma. Further investigations at a genetic level should be encouraged, not only to define the role of KIT in the oncogenesis of thymic epithelial tumors, but also to establish target-based therapy.
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ABSTRACT: To study KIT (CD117) expression in thymic epithelial tumors in China, and investigate diagnostic and clinical significance. Thymic epithelial tumors (TETs) from 102 patients (3 type A, 29 type AB, 5 type B1, 22 type B2, 29 typeB3 and 16 thymic carcinomas) were examined. Immunohistochemical staining with an antic-kit monoclonal antibody was performed on a tissue microarray. Relationships between KIT positive expression and the TET clinical characteristics (WHO histologic classification and Masaoka stage system) were analysed. The KIT positive expression rate was significantly higher in thymic carcinoma (60%, 9/16) than in thymoma (8%, 7/86), a strong correlation being found with the WHO classification, but not the Masaoka tumor stage. The overall survival for patients with KIT positive lesions was significantly worse. KIT is a good molecule marker to differentially diagnose thymic carcinoma from thymoma, while also serving as a predictor of prognosis for TETs. Further research into KIT mutations in Chinese TETs should be conducted to assess the efficacy of targeted therapy.Asian Pacific journal of cancer prevention: APJCP 06/2012; 13(6):2745-8. DOI:10.7314/APJCP.2012.13.6.2745
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ABSTRACT: It is sometimes difficult to differentiate between type B3 thymoma from thymic carcinoma histologically. Given the rarity of these tumours, studies have been limited. A series of 66 thymic neoplasms were reviewed and classified according to the World Health Organization (WHO) scheme. We performed a tissue microarray analysis of surgically resected thymic tumour specimens including 12 thymic carcinomas, 17 type B3 thymomas and 37 thymomas of other types. Percentage and staining intensity of immunohistochemical markers were recorded. Tumour eosinophilia was recorded positive if at least one eosinophilic cell identified. Positive staining of the following markers significantly differentiated type B3 thymoma from thymic carcinoma: cytokeratin 5/6 (15 vs. 3), Mesothelin (0 vs. 5), cytoplasmic androgen receptor (10 vs. 0), CD57 (9 vs. 0), CD5 (0 vs. 7), TdT (lymphocytic) (14 vs. 1), CD1a (lymphocytic) (14 vs. 2), CD117 (1 vs. 9), MOC31 (2 vs. 6), p21 (2 vs. 8), cytoplasmic Survivin (0 vs. 4), and tumour eosinophilia (1 vs. 11). Combining two or three markers was able to differentiate these two tumours with area under the curve percentage of at least 92%. Tumour eosinophilia combined with a panel of immunohistochemistry could differentiate type B3 thymoma from thymic carcinoma.International Journal of Experimental Pathology 11/2010; 92(2):87-96. DOI:10.1111/j.1365-2613.2010.00745.x