胃リンパ球浸潤性髄様癌の肉眼形態学的特異性

Medullary Carcinoma with Lymphocytic Infiltration of the Stomach with Attention to Characteristic Gross Appearance

要旨　胃リンパ球浸潤性髄様癌（medullary carcinoma with lymphocytic infiltration; MCLI）は，分化度の低い癌細胞の髄様増殖と間質における著明なリンパ球浸潤を特徴とする特異な組織型であり，進行癌であっても極めて良好な術後経過をとることは，本疾患の術前診断や術後経過観察を含めた臨床的取り扱いを考えるうえで重要である．このような観点から本研究では，30例の胃MCLI症例（早期癌7例，進行癌23例）を腫瘍の肉眼型に着目して検討し，その組織形態学的概念と臨床（肉眼）診断との接点について考察した．胃MCLIの典型的肉眼像は，早期癌ではⅡa＋Ⅱc型，進行癌ではBorrmann2型に代表される境界明瞭な潰瘍形成性限局型腫瘍であった．このような特徴のほかに，2例の早期癌と10例の進行癌の肉眼所見は分類不能型と判定された．この12例のうち，早期癌2例と進行癌7例の原発腫瘍は，悪性リンパ腫の潰瘍型ないしは決壊型の肉眼所見と類似していた．また3例の進行癌は，粘膜下腫瘍に極めて類似した肉眼所見を呈していた．腫瘍の肉眼型と好発部位，組織学的諸因子，浸潤リンパ球のsubpopulation，リンパ節転移や予後との間には特定の関係は認められなかった．胃MCLI症例は進行癌であっても極めて良好な術後経過を示し，再発死亡した4例はいずれも漿膜に浸潤し，リンパ節転移を伴う高度進行癌であった．胃MCLIの特異的な肉眼像と極めて良好な術後生存率を考慮すると，治療前（術前）診断が本疾患の臨床的取り扱いに際して重要であり，超音波内視鏡検査やjumbo biopsyは有用な補助手段であると考えられた．

　Medullary carcinoma with lymphocytic infiltration (MCLI) of the stomach is a unique neoplastic entity, characterized histologically by the sparse population of small nests of poorly differentiated carcinoma cells and intense and diffuse lymphocyte infiltration, and clinically by an excellent prognosis. Such histopathological and clinical implications encouraged us to investigate 30 patients with gastric MCLI, including seven with early MCLI and 23 with advanced MCLI, paying particular attention to gross findings. Representatively, gastric MCLI grossly showed a sharply demarcated, raised border and an ulcerated center, corresponding to Ⅱa+Ⅱc type and Borrmann 2 type in early and advanced carcinomas, respectively. The other striking gross characteristic was that, in two cases of early MCLI and 10 cases of advanced MCLI, gross findings of the tumor could not be included under any of the classifications of the Japanese Research Society for Gastric Cancer. These 12 tumors showed variable curious configurations, that is, two early MCLI and seven advanced MCLI appeared to be malignant lymphoma, and the other three advanced MCLI resembled submucosal tumor. The gross appearance of gastric MCLI did not correlate with the site, histopathologic factors, lymphocyte subpopulations, lymph node metastasis, or prognosis. Postoperative surveillance revealed that only four patients with the tumor showing serosal invasion and extensive nodal involvement had died of recurrence. Although gastric MCLI is a histopathologic entity, the unique gross appearances and favorable postoperative survival suggest that preoperative diagnosis is important for clinical management of the patients. Endoscopic ultrasound and jumbo biopsy could be useful for clinical evaluation of this tumor.