胃原発悪性リンパ腫の病理学的特徴

Pathological Feature of Primary Gastric Lymphoma

要旨　胃をはじめとする節外組織には多くの場合，先天的にリンパ濾胞の形成は認められない．このことからもリンパ節を構成するリンパ球とはその性質や機能が異なると考えられる．胃にはリンパ節と同様に様々な型の悪性リンパ腫がみられるが，Bリンパ腫がほとんどで，びまん性大細胞型，びまん性中細胞型が多い．Tリンパ腫の発生は非常にまれである．これらの悪性リンパ腫は組織発生上，前濾胞中心細胞，濾胞中心細胞および後濾胞中心細胞由来に分けられ，組織学的，免疫組織化学的に分類できる．これらの特徴により分類できないとき，免疫グロブリンやTレセプターの再構城，更にbcl-1やbcl-2などを用いた分子生物学的所見が参考となることもある．Isaacsonらの提唱したMALTリンパ腫は粘膜を有する節外性組織にのみ認められる．その特異な細胞像や免疫組織学的所見からマントル層外層（marginal zone）のリンパ球由来が考えられている．

　Most primary gastric lymphomas are B-cell lymphomas. According to the LSG classification, more than 90% of all malignant lymphomas of the stomach are diffuse lymphoma (DL). Diffuse large-cell type lymphoma (DL-large) is the most commonly observed case in the stomach as well as among nodal lymphomas, and the medium-sized-cell type (DL-medium) is also frequently found. Using immunohistochemical study, the histogenesis of gastric lymphoma is classified as being of prefollicle, follicle and postfollicle center cell origin. Follicular lymphomas and the majority of DL-large are positive for CD 10, suggesting follicle center cell origin. DL-medium, positive for sⅠgD, CD 5 or ALPase, is encounterd as being prefollicle center cell, corresponding to mantle zone lymphocytes. DL-small (lymphoplasmacytoid) and DL-large (immunoblastic type) with monoclonal cytoplasmic immunoglobulin usually originate from postfollicle center cell outside of the follicle. MALT lymphoma proposed by Isaacson is characterized by extranodal-site occurrence. These were mainly observed in the gastrointestinal tract, thyroid gland, bronchus, salivary gland and thymus, etc. MALT lymphoma is considered to arise from the marginal zone of the follicle, which we call the outer layer of the mantle zone.