大腸カルチノイドの診断と長期経過

Clinicopathological Features and Long-term Outcomes of Endoscopically Resected Rectal Neuroendocrine Tumors

要旨●当院で内視鏡治療を施行した直腸NET病変を対象に，臨床病理学的特徴と長期成績を検討した．1997〜2011年に治療した90病変の腫瘍径中央値は5mmで，すべて粘膜下層にとどまるNET G1病変であった．内視鏡治療後，経過観察期間中央値76.1か月の間に1例も再発，転移を認めておらず，内視鏡治療の有効性が示唆された．これらの病変の脈管侵襲について，免疫組織化学染色・特殊染色で新たに再評価した結果，計42病変（46.7％）で陽性となった．固有筋層浸潤のない小さな直腸NET G1病変でも高い割合で脈管侵襲陽性がみられ，かついずれも再発・転移を来さなかったことより，このような病変における脈管侵襲陽性は追加外科的切除の絶対的条件にはならない可能性が考えられた．

　We retrospectively examined the clinicopathological features and long-term outcomes of rectal NETs（neuroendocrine tumors）treated by ER（endoscopic resection）at National Cancer Center Hospital, Tokyo, Japan. Regarding the 90 NET lesions treated between 1997 and 2011, the median tumor size was 5mm, and all were confined to the submucosal layer. The Ki-67 index was less than 3％ in all lesions ; therefore, they were classified as NET G1. Elastic-staining and double-staining immunohistochemistry revealed the presence of lymphatic and venous invasion in 23（25.6％）and 35 lesions（36.7％）, respectively. Collectively, lymphovascular invasion was identified in 42 lesions（46.7％）. All cases were followed up without additional surgery, and no metastasis or recurrence was detected during the median follow-up period of 76.1 months. These favorable long-term outcomes indicate the usefulness of ER. The finding of highly prevalent lymphovascular invasion in small rectal NET G1 lesions raises a question regarding the significance of lymphovascular invasion as a risk factor for metastasis of such lesions.