Abstract
Pathological investigation was done in 36 cases of colorectal cancer with invasion to proper muscle layer (pm cancer) and 64 cases of early colorectal cancer to know the developmental process of colorectal cancer. Pm cancers were macroscopically classified into three types according to the rules of colorectal cancer and gastric cancer, namely, type I, type II, and IIa+IIc like pm cancer. Microscopically, pm cancers were classified into four grade by vertical invasion in the proper muscle layer. It became apparent that vertical invasion of type I and ha +IIc like pm cancers were mild (grade lor2), and their sizes were almost less than 3 cm in diameter. In contrast, type II pm cancer tended to invade deeply (3 or 4) and their sizes were more than 4 cm in 17 of 23 cases. Although advanced colorectal cancer with subserosal invasion appeared grossly type II in most cases, 28% of pm cancers showed type I in gross appearance. Particularly, in the sigmoid colon, type I/type II ratio of pm cancer was 1 which was significantly higher than that of rectum (0.3). Survey of early cancers in the present study revealed that a group of tall early cancers consisted of Ip, Isp, and Is was predominantly in the sigmoid colon. Therefore, it was suggested that in the sigmoid colon, a group of tall early cancers grew slowly and developed into type II pm by way of type I pm cancer. Ratio of cancers associated with adenoma was 74% in mucosal cancer, 33% in submucosal cancers and 0% in pm cancer. Therefore, it was suggested that early colorectal cancer lost a component of adenoma in the process of developing into pm cancer.
