食道癌に対する粘膜切除の適応―その病理学的基盤

Pathological Basis of Endoscopic Mucosectomy of Superficial Esophageal Carcinoma

要旨　食道癌に対する粘膜切除の適応を検討する目的で外科的に切除された食道表在癌61症例87病変（sm癌41症例，mm癌13症例，ep癌7症例）と食道進行癌に合併した食道表在癌を含む食道表在癌全病変117病変（sm癌53病変，mm癌29病変，ep癌35病変）について深達度と脈管侵襲，リンパ節転移の頻度について検討した．深達度epの病変では脈管侵襲，リンパ節転移は全く見られず食道表在癌の粘膜切除の絶対適応となりうる．深達度epの診断で内視鏡切除され，切除標本の組織学的検討からmm₁では，浸潤はごく限局し，脈管侵襲，リンパ節転移の可能性も低く，追加治療は必ずしも必要ではない．mm₃以深の浸潤が認められた場合には脈管侵襲，リンパ節転移を認めることがあり，根治を目的とする内視鏡治療の対象にはならないと考えられ，外科的切除とリンパ節郭清を追加すべきと考える．mm₂の浸潤が認められた場合には脈管侵襲は少ないものの未だ問題が残る．分割切除については最深達部が切除断端にかからないように切除されることが重要で，それぞれの切除片相互の位置関係が切除標本の再構築写真や切り出し写真と組織標本によって評価できるのであれば患者の“quality of life”を考慮した治療法として分割切除を行うことも相対的な適応となりうる．また食道癌は多発例が多く，内視鏡的粘膜切除後の厳重な経過観察が必要である．切除された材料から適切かつ十分な病理組織標本を作製することが内視鏡治療の根治性についての評価に重要であり，病理の対応の仕方が根治性の評価を規定すると言える．

　Endoscopic mucosectomy of esophageal cancer is now performed in several institutes. To determine the indication for endoscopic mucosectomy, pathological basis was analyzed in 117 lesions. Eighty seven lesions were from 61 operated cases of superficial carcinoma, and the other lesions were accompanied with advanced cancers. They were composed of 35 ep-cancers, 29 mm-cancers and 53 sm-cancers. Mm-cancers and sm-cancers were subclassified into mm₁, mm₂, mm₃, and sm₁, sm₂, sm₃ respectively. Vascular invasion and lymph node metastasis were analyzed based on this subclassification.

　In ep-cancers, neither vascular invasion nor lymph node metastasis was found, suggesting that the epcancer was an absolute indication for endoscopic mucosectomy. The characteristics of mm₁-cancer was almost similar to those of ep-cancer, because the mm₁-cancer still had most of the continuous basement membrane. One out of five mm₃-cancers had lymph node metastasis and vascular invasion. Thus, mm₃-cancer was not an indication for endoscopic mucosectomy. There was controversy over the indication of mm₂ cancer. Even though none of seven cases in our studies had vascular invasion and lymph node metastasis, the lamina propria mucosa of the esophagus has rich networks of the lymphatics and vessels, further study should be done concerning histological type and mode of invasion of carcinoma in relation to lymphatic invasion and lymph node metastasis in mm₂-cancer.

　Another problem was multifocality of the esophageal cancer. The incidence of multifocal esophageal cancers was very high as 20～30%. A careful follow up should be continued after mucosectomy. The purpose of endoscopic mucosectomy for cancer was complete resection. Therefore, histological examination of the resected specimen was essential. We demonstrated how to fix and examine the resected specimen with photographs.