Non-polypoid colorectal neoplasias: a multicentric study.

A total of 781 non-polypoid colorectal neoplasias harvested at 4 main Hospitals in Tokyo, Japan (n =420) and at 4 different time-intervals at the Karolinska Hospital, Stockholm, Sweden (n=361) were reviewed. By applying strict histologic definitions, the lesions were classified into adenomas with low grade dysplasia (LGD), with high grade dysplasia (HGD), intramucosal carcinomas (IMC) or submucosal carcinomas (SMC). Of the non-polypoid neoplastic lesions reviewed in Sweden, 82.8% (n =299) had LGD. In Japanese patients only 42.6% (n=179) had LGD (p ≤ 0.001). On the other hand, as many as 42.4% (n=178) of the non-polypoid lesions in Japanese patients had HGD, but only 14.1% (n=51) of those in Swedish patients (p ≤ 0.001). Whereas 15.0% (n=63) of the non-polypoid neoplasias seen in Japan were IMC or SMC, only 3.0% (n =11) of those seen in Sweden were IMC or SMC (p ≤ 0.001). The cause(s) for these differences remains unclear. In Japan, however, a marked increased incidence of colonic cancer has been recorded in later years. Whether the catching up phenomenon by the Japanese with western colonic cancer incidence includes increased histologic aggressiveness of non-polypoid neoplastic polyps -as found in this survey- remains to be elucidated.