濾胞性リンパ腫―その今日的理解と病理診断を中心に

Follicular Lymphoma―A Current Concept and Pathological Diagnosis

要旨　濾胞性リンパ腫ほど臨床病態，病理組織像，ならびに分子病態が明確なものは他に類をみない．本病型の頻度はびまん性大細胞型B細胞性リンパ腫に次いで高く，まれな病型とは言い難い．消化管診療の現場では胃腸管発生例に遭遇しうるが，本病型はあくまで節性優位である．新訂WHO分類では，本病型を，胚中心細胞に類似する小～中型B細胞と胚中心芽細胞に類似する大型B細胞とが種々の割合で混在し，少なくとも一部で独立性のあるリンパ濾胞様結節を形成する腫瘍と定義している．本病型の病理診断は特有の結節構造を認識することから始まる．精度の高い病理診断の遂行には，採取臓器の種類を問わず，挫滅のない十分量の組織が必要である．ゆえに情報量の乏しい針生検組織や小さな鉗子生検組織は病理診断には不適であり，その評価と解釈は常に慎重に行われるべきである．

　Follicular lymphoma (FL) has distinctive clinical, pathologic, and cytogenetic features. FL is the second most common form of malignant lymphoma, after diffuse large B-cell lymphoma, and it accounts for approximately 18 percent of the 2,260 cases of lymphoid neoplasms diagnosed during the period 2001-2006 in Japan. It is noteworthy that the frequency of FL has increased compared with a previous nationwide study in 2000. The majority of FL arise in lymph nodes. In fact, FL show primary extranodal manifestations in only 10.4 percent (almost all involving the intestine). Histologically, FL is defined as a lymphoid neoplasm of germinal center B-cells (centrocytes and centroblasts), which has at least a partially follicular growth pattern. Diagnosis of FL should be made based upon an excisional biopsied-specimen. Needle biopsies from the edges of a mass may cause problems in histologic diagnosis, because the clinician may remove the most accessible nodal/extranodal mass, which is often too small to represent adequately the disease process. The largest accessible mass should be biopsied, because it has the greatest chance of showing specific abnormalities. Special care should also be taken to excise the entire lymph node in one piece, including its capsule and, if possible, a rim of pericapsular fibro-adipose tissue, which often provides important clues of haemato-lymphoid disease.