発育進展の経過が追えたPG type隆起型早期大腸癌の1例

Development and Progression of Polypoid Growth Type（PG）Early Colorectal Cancer, Report of a Case

要旨●患者は60歳代，男性．便潜血陽性精査目的に前医で施行した下部消化管内視鏡検査で上部直腸に早期大腸癌を疑われ，精査加療目的に当科へ紹介となった．治療前の精査ではPG typeの中心陥凹を伴う10mm大の亜有茎性病変として観察されたが，2か月後の治療時にはNPG typeと考えられる，辺縁に腫瘍成分を伴わない6mm大の陥凹性病変へと形態変化が認められた．粘膜下層深部浸潤が疑われたが，完全摘除生検目的に内視鏡治療の方針とした．切除標本の病理組織学的所見は，pT1a（500μm）の中分化型管状腺癌で，脈管侵襲陰性，簇出Grade 1であった．辺縁部の粘膜表面には正常腺管が認められ，NPG typeとした術前内視鏡評価に矛盾のない所見であった．PG typeを考える隆起型腫瘍から，NPG typeを考える陥凹型腫瘍へと形態変化した経過を追えたことから，通常NPG typeとされる0-IIc型SM癌の中にもPG type由来のものが含まれている可能性を示唆する貴重な症例であると考えられた．

　A 60-year-old male was referred to our hospital after a colonoscopy revealed early colorectal cancer in the upper rectum. Investigative colonoscopy in our department revealed a 10-mm semipedunculated polyp, which was considered as PG（polypoid growth）-type cancer. Two months later, however, treatment colonoscopy revealed a 6-mm superficial depressed lesion with morphological changes. Endoscopic findings of the marginal area of the tumor suggested normal mucosa, which was considered as NPG（non-polypoid growth）-type cancer. Although we diagnosed this tumor as submucosal invasive colorectal cancer, endoscopic submucosal dissection was performed for total excisional biopsy. The pathological diagnosis was moderately differentiated tubular adenocarcinoma, which had invaded 500μm into the submucosal layer without lymphovascular invasion. The marginal area of the tumor had a normal gland component, which corresponded to the endoscopic findings, suggesting an NPG-type cancer. Based on the endoscopic findings, we identified morphological changes distinguishing between PG-type cancer and NPG-type cancer. These results suggest that superficial depressed colorectal cancer, which was generally considered an NPG-type cancer, might include PG-type cancers, as in this case.