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Presented by George Netto, MD and prepared by Shien Micchelli, M.D.
Case 5: A 55 year old male complaining of shortness of breath.
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1. Question
Week 258: Case 5
A 55 year old male complaining of shortness of breath was found to have a 7 cm cystic, anterior mediastinal, mass on chest x-ray.images/2_27_06_5a.jpg
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images/2_27_06_5e.jpgCorrect
Answer: Thymoma, minimally invasive with extensive regressive changes
Histology: The extensive tumor necrosis is associated with paucity of lymphocytes, prominent infiltration of histiocytes and focal fibroblastic reaction. The residual viable tumor maintained a lobulated architecture and is composed of a dense population of small lymphocytes (CD3 positive) outnumbering admixed neoplastic large polygonal epithelial cells. The latter are highlighted with cytokeratin AE1/AE3 and contain enlarged vesicular nuclei with conspicuous nucleoli resembling the predominant epithelial cells of thymic cortex. Emperipolesis is demonstrated in many epithelial cells while anaplasia is absent. The above features are those of a Type B2 Thymoma in the WHO classification. The thick tumor capsule is focally breached indicating tumor microinvasion into surrounding mediastinal fat (Masaoka stage: 2a, TNM: pT2).
Discussion: The extensive regressive changes demonstrated in our case can occur either spontaneously or as a result of prior corticosteroids treatment. Although both B2 and B1 thymomas are lymphocyte rich, differentiating B2 from B1 thymoma is based on the lack of medullary islands and the presence of a more conspicuous epithelial component in B2 thymoma. In B3 thymoma the epithelial cells are even more prominent forming sheets and nodules with markedly fewer lymphoid elements. Stage and respectability are the two most important predictors of outcome in B2 thymoma. Overall, B2 thymomas have a higher malignant potential compared to B1 type but are less aggressive than B3 tumors.
Reference(s):
– Okumura M, Ohta M, Tateyama H, Nakagawa K, Matsumura A, Maeda H, Tada H,Eimoto T, Matsuda H, Masaoka A. The World Health Organization histologic classification system reflects the oncologic behavior of thymoma: a clinical study of 273 patients. Cancer. 2002;94(3):624-32.
– Quintanilla-Martinez L, Wilkins EW Jr, Choi N, Efird J, Hug E, Harris NL. Thymoma. Histologic subclassification is an independent prognostic factor. Cancer. 1994;74(2):606-17.Incorrect
Answer: Thymoma, minimally invasive with extensive regressive changes
Histology: The extensive tumor necrosis is associated with paucity of lymphocytes, prominent infiltration of histiocytes and focal fibroblastic reaction. The residual viable tumor maintained a lobulated architecture and is composed of a dense population of small lymphocytes (CD3 positive) outnumbering admixed neoplastic large polygonal epithelial cells. The latter are highlighted with cytokeratin AE1/AE3 and contain enlarged vesicular nuclei with conspicuous nucleoli resembling the predominant epithelial cells of thymic cortex. Emperipolesis is demonstrated in many epithelial cells while anaplasia is absent. The above features are those of a Type B2 Thymoma in the WHO classification. The thick tumor capsule is focally breached indicating tumor microinvasion into surrounding mediastinal fat (Masaoka stage: 2a, TNM: pT2).
Discussion: The extensive regressive changes demonstrated in our case can occur either spontaneously or as a result of prior corticosteroids treatment. Although both B2 and B1 thymomas are lymphocyte rich, differentiating B2 from B1 thymoma is based on the lack of medullary islands and the presence of a more conspicuous epithelial component in B2 thymoma. In B3 thymoma the epithelial cells are even more prominent forming sheets and nodules with markedly fewer lymphoid elements. Stage and respectability are the two most important predictors of outcome in B2 thymoma. Overall, B2 thymomas have a higher malignant potential compared to B1 type but are less aggressive than B3 tumors.
Reference(s):
– Okumura M, Ohta M, Tateyama H, Nakagawa K, Matsumura A, Maeda H, Tada H,Eimoto T, Matsuda H, Masaoka A. The World Health Organization histologic classification system reflects the oncologic behavior of thymoma: a clinical study of 273 patients. Cancer. 2002;94(3):624-32.
– Quintanilla-Martinez L, Wilkins EW Jr, Choi N, Efird J, Hug E, Harris NL. Thymoma. Histologic subclassification is an independent prognostic factor. Cancer. 1994;74(2):606-17.
