リンパ球浸潤胃癌―病理の立場から

Pathological Characteristics of Gastric Carcinoma with Lymphoid Stroma

要旨　胃のリンパ球浸潤癌は腫瘍組織内外にリンパ球浸潤が高度な組織型で，EBV（Epstein-Barr virus）感染が高頻度に関連している．「胃癌取扱い規約第14版」では低分化腺癌充実型（por1）から特殊型として独立した位置づけとなった．当院で治療した胃癌症例からリンパ球浸潤癌を抽出し，EBV陽性群とEBV陰性群に分類して臨床病理学的に検討した．リンパ球浸潤癌は59例で胃癌全体の2.5％，EBV陽性群は43例（73％），EBV陰性群は16例（27％）であった．肉眼型は早期癌では混合型が，進行癌では2型が多く，粘膜下腫瘍の形態をとるものが多く認められた．深達度は粘膜下層症例が多く（61％），粘膜癌は1例も認めなかった．EBV陽性群は男性優位が顕著（84％）で，胃の近位部に大部分（95％）が存在していた．組織学的には粘膜下以深でリンパ球浸潤癌の特徴を示すが，粘膜内成分では中分化型管状腺癌（tub2）にリンパ球浸潤を伴うlace patternの性質を有していた．EBV陽性群の大部分（86％）が腺境界部に存在していた．リンパ球浸潤癌は予後良好な症例が多く，腫瘍の性質に応じた治療を行うためにも，肉眼診断，生検診断の時点で予測をつけることが重要と考えられた．

　GCLS（gastric carcinoma with lymphoid stroma）is a histological type with severe lymphocytic infiltration around and in the carcinoma tissue. Most of it is associated with the infection by the EBV（Epstein-Barr virus）. In the 14th edition of the Japanese classification of gastric carcinoma, the type has been classified as a special type in histology, independent of the solid type of poorly differentiated adenocarcinoma in the 13th edition. We selected the cases of GCLS from the gastric carcinomas treated in our hospital. We carried out in them in situ hybridization for EBV-encoded small RNA and classified the EBV-positive and the EBV-negative group. There were 59cases of GCLS's（1.3％ of the total cases of gastric carcinoma）. There were 43 EBV-positive cases and 16 EBV-negative cases. In the total GCLS cases, the macroscopic type tended to be mixed type such as 0-IIa＋IIc in the early cases and type 2 in the advanced cases including a submucosal tumor-like lesion. For the depth of invasion, most of the GCLS's were submucosal cancers, and no mucosal cancers were identified. Clinical features of the EBV-positive group included male predominance with the proximal stomach as the preponderant location. Histologically, although GCLS was observed in the submucosa, it was more noticeable in the mucosa, and lace pattern showing irregularly anastomosing cord-like or tubular structures was also observed. The background mucosa in the EBV-positive group showed an intermediate zone of gastric gland with moderate or severe lymphocytic infiltration and little association with intestinal metaplasia. As GCLS is a special type of gastric cancer with better prognosis, at the time of endoscopic exam or biopsy, GCLS should be analyzed in order to determine treatment suitable for the characteristics of the tumor.