印環細胞癌の組織分類における最新知見

Recent Progress in the Histopathological Classification of Gastric Signet-ring Carcinoma

要旨●世界的に胃癌の発生率は減少しているものの，欧米では印環細胞癌の発生率が増加しているため印環細胞癌への関心が高まっている．印環細胞癌は，本邦の胃癌取扱い規約では一般型の一つとして分類されてきたが，WHO分類では第4版で一時的にpoorly cohesive carcinomaの一亜型とされたものの，第5版で独立した組織型として復活した．近年，欧州の研究グループが印環細胞癌の定義の曖昧さや病理診断の標準化の欠如を改善するために，印環型細胞の占める比率に基づく新たな定義を提唱した．まだ国際的にコンセンサスは得られていないが，今後印環細胞癌の診療や研究に影響を与えると思われる．また，層構造や腸型形質発現の有無と悪性度との関連，遺伝性胃癌など，印環細胞癌に関連する研究成果が近年注目されている．

　Although the incidence of gastric cancer is decreasing worldwide, that of signet-ring cell carcinoma is increasing in the western countries. Therefore, more attention needs to be paid to tumors. Signet-ring cell carcinoma has been classified as one of the common histological subtypes in the Japanese classification. Whereas, signet-ring cell carcinoma has been classified as poorly cohesive carcinoma according to the 4th edition of the World Health Organization classification ; however, it was revised as an independent histological type in the 5th edition. To improve the ambiguity of the definition of signet-ring cell carcinoma and the lack of standardization of its pathological diagnosis, a European research group proposed a novel definition based on the proportion of signet-ring cells in tumor. Although no international consensus has been reached yet, it may affect medical care and research of signet-ring cell carcinoma in the future. In addition, the relationship between the presence or absence of a layered structure and the expression of intestinal phenotype in signet-ring cell carcinoma, biological behaviors, and hereditary gastric cancer have recently attracted attention.