Ⅱc型直腸早期癌―de novo発生の1例

Ⅱc (depressed) Type of Early Carcinoma of the Rectum Originating “de novo”, Report of a Case

　大腸の早期癌は，潰瘍性大腸炎の癌化例や大腸腺腫症の特殊例を除けば，ほとんどが隆起型と考えられており，このことは大腸癌の組織発生と早期発見，治療を考えるうえでの最も基本的な知見とされている．大腸癌の組織発生については，腺腫先行説（adenoma-carcinoma sequence）とde novo発生説があるが，腺腫内癌（carcinoma in adenoma）の存在などから，ほとんどの大腸癌は腺腫に由来するものと信じられている．一方，腺腫を併存しないde novoと思われる微小癌の報告も少数みられるが，いずれも隆起性病変で完全な陥凹型早期癌の報告はみられず，これらについてもadenoma-carcinoma sequenceを完全には棄却しえない．

　最近われわれは，大腸検診を契機にして発見されたⅡaを併わない単発のⅡc型直腸sm癌の手術例を経験した．この症例について詳細な組織学的検索を行った結果，これまで報告をみないde novoに発生した早期の印環細胞癌と考えられたので，組織発生と形態発生に検討を加えて報告する．

　A 33-year-old man visited to the Kanagawa Health Service Association on December 10th, 1980 for barium enema study and sigmoidoscopy because of a positive fecal occult blood test result observed after mass screening for colorectal cancer. Both examination revealed no abnormality on the mucosal surface of the upper rectum and rectosigmoid except for a small polyp at the lower rectum. He was referred to our hospital for endoscopic polypectomy.

　Colonoscopy on January 8th, 1981 detected a very shallow depression with a finely granular surface at the anterior wall of the upper rectum. Biopsy specimens demonstrated diffuse infiltration of typical signetring cells among the normal glands.

　Subsequent colonoscopy on admission, February 10th, 1981 revealed that the lesion had increased in size and depth similar to an early gastric cancer of Ⅱc (depressed) type, while barium enema failed to demonstrate the lesion.

　Low anterior resection was performed with extensive lymph node dissection. The operative specimen revealed a well-defined very shallow depression, type Ⅱc, 1.3×1.9×0.1 cm, at the upper rectum.

　Histologically, according to the serial sections, the lesion disclosed extensive infiltration of typical large signet-ring cells in the propria mucosa without evidence of the adenomatous glands. There existed few foci of the neoplastic invasion to the submucosal layer with occasional lymphatic permeation. HID-AB stain revealed sialomucin-positive neoplastic cells. Lymph node involvement was not detected in dissected 72 nodes.

　This is the first case of a typical early carcinoma of the colo-rectum showing a superficial depression, type Ⅱc, in morphological pattern with a strong presumptive evidence of “de novo” origin. Signet-ring cell carcinoma could rise “de novo” and progress in the shape of superficial depressive type of early carcinoma. It is emphasized that early detection of the depressive type of carcinoma requires endoscopic biopsy on every questionable lesion of finely granular colonic mucosa in mass screening for colorectal cancer.