早期胃癌EMR/ESDの絶対適応病変を決定するための術前内視鏡診断と問題点—深達度診断—EUS

Preoperative Endoscopic Diagnosis and Issues for Determining the Absolute Indication of EMR/ESD for Early Gastric Cancer：Diagnosis of Invasion Depth：EUS

要旨●早期胃癌の深達度診断においてEUSは有用であるが，通常内視鏡検査（CE）に対する上乗せ効果に関しては不明な点も多い．治療前精査症例を対象にした筆者らの検討では，簡便な診断基準に則ったCEの正診率は，EUSと有意差なく粘膜癌では90%を超えていたものの，深部浸潤癌では65%と低かった．一方，EUSはCEで深読みした粘膜癌の約6割を正診していた．そこで，CEで深部浸潤を疑った症例に対してのみEUS診断を適用しCEとEUSを組み合わせると，CE単独・EUS単独での診断に比して有意に正診率が向上したことから，粘膜癌はCEで診断し，深部浸潤を疑う病変に対してのみEUSを行う方法が効率的で正確な診断を可能にすることが示唆された．EUSの付加価値は限定的であると考えられ，特性を理解し役割を明確にしながら診断に用いる必要がある．

　The additional value for using EUS to predict the invasion depth of early gastric cancer has not been fully clarified. Therefore, we retrospectively compared the diagnostic abilities of CE（conventional endoscopy）and EUS among 230 patients who underwent pretreatment examinations. The accuracy rate of CE was 73〜82%, which was based on the findings of irregular surface and submucosal tumor-like marginal elevation as the simple diagnostic criteria for deep invasion. The accuracy rate for mucosal cancer in CE was 93%, whereas that for submucosal invasive cancer was 65%. In EUS, 62% of mucosal cancers, which were over-estimated in CE, were diagnosed correctly.

　If EUS is applied and combined only for cases suspected of deep invasion on the basis of CE findings, the accuracy rate improves to 86〜90%, which is significantly higher than that for CE alone or EUS alone. Thus, an integrated strategy that diagnoses mucosal cancer only with CE and performs EUS for lesions suspected of submucosal deep invasion on the basis of CE findings may offer a more efficient and accurate diagnosis. The validity of the algorithm and the auxiliary effects of EUS are currently being assessed in a multicenter prospective study. Considering the limited value of EUS, it is necessary for us to understand its characteristics and perform it appropriately to receive more accurate diagnoses.