Abstract
Background and Study Aims: Based on Japanese case studies, we examined whether colorectal mini-de novo carcinoma
also occurs outside Japan. We defined mini-de novo carcinomas as carcinomas infiltrating
the submucosa, with a maximum diameter of 10 mm, and with no evidence of precursive
adenomatous tissue.
Patients and Methods: Between 1988 and 1994, we diagnosed carcinomas of this type in polypectomy and surgical
resection specimens from 155 patients. These mini-de novo carcinomas did not differ
from carcinomas arising from adenomas in terms of patient age (median 67.1 years),
sex distribution (men : women 0.96 : 1), or location-they occurred primarily in the
sigmoid (53 %) and rectum (27.3 %).
Results: Most of the mini-de novo carcinomas were macroscopically of the polypoid type (59.4 %);
flat, elevated carcinomas were also relatively frequent, including those with a central
concave depression (21.9 %) and those without a depression (12.3 %). Histologically,
all of the lesions without exception were adenocarcinomas (grade 1 : 28.4 %, grade
2 : 65.8 %, grade 3 : 5.8 %). There was carcinomatous invasion of submucosal lymphatic
or blood vessels in 20 %.
Conclusions: Our analysis shows that colorectal mini-de novo carcinoma is not a purely Japanese
phenomenon, and that these carcinomas are being diagnosed with increasing frequency
as the awareness of their existence and macroscopic growth characteristics increases.
