胸腺腫ならびに胸腺癌の病理・生物学的特徴

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Thymoma is defined as an epithelial tumor of low grade malignancy, more or less associated with immature T lymphocytes, whose biological behavior cannot be predicted by histology alone. On the other hand, thymic carcinoma is made up of obviously atypical epithelial cells arranged in nests or proliferating diffusely and is not associated with immature T lymphocytes. Epithelial cells of thymoma were positive not only for keratin but also Leu 7. However, Leu 7 positive thymic carcinomas were rare. OKT 6 positive immature T lymphocytes were seen without exception in thymoma but not in carcinoma. OKT 6 negative, Leu 3a or Leu 2a positive mature T lymphocytes were present in areas with medullary differentiation in thymoma. These immunohistochemical findings are of help in differential diagnosis of thymic epithelial tumors, when difficult with histology alone. Most important factor associated with poor prognosis of patients with thymoma is invasive growth of the tumor. However, our recent studies disclosed that nuclear area, mean nuclear DNA content, DNA histogram pattern, occurrence of aneuploidy, immunohistochemical expression of β2-microglobulin and HLA-DR α-chain, infiltration of S100β positive small lymphocytes, and glandular differentiation in carcinoma were more or less associated with degree of malignancy in thymic epithelial tumors, or might be useful for distinction between thymoma and thymic carcinoma. As for the development of thymic epithelial tumors, integration of Epstein-Barr virus DNA in tumor cell DNA was found in only one thymic carcinoma among 21 thymomas and four thymic carcinomas. This single tumor was undifferentiated (malignant lymphoepitheliomalike) carcinoma resembling nasopharyngeal carcinoma of the same name histologically, and was found to be of clonal growth by Southern blot analysis of the terminal repeat of the virus genome. Not included in this paper were thymic epithelial tumors associated with myasthensia gravis, since patients with thymoma presenting symptoms of myasthenia gravis rarely visited cancer hospitals.
特定非営利活動法人日本呼吸器外科学会の論文
1990-11-15

胸腺腫ならびに胸腺癌の病理・生物学的特徴

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