Flat-type early colorectal cancer preferentially develops in right-sided colon in older patients.
BACKGROUND
Flat-type colorectal cancer is frequently reported in Japan and Europe, but its clinical features remain obscure. Thus, we investigated the clinical features of flat-type early colorectal cancer with respect to tumor location and patient age and compared them with those of polypoid-type early and advanced cancer.


METHODS
Between January 1999 and June 2001, total colonoscopy was performed in 6,178 patients (mean age, 61 years; 4,290 males and 1,888 females). Of these patients, 402 patients with 429 colorectal cancers were found: 202 at advanced stage (invading beyond muscularis propria) and 227 at early stage (carcinoma in situ or invading within submucosa). Early-stage cancer was classified into two macroscopic subgroups: flat-type and polypoid-type.


RESULTS
Out of 227 early cancers, 44 were flat type and 183 were polypoid. Flat-type early cancer was more frequently located in the right colon (57 percent, 25/44) than polypoid-type cancer (19 percent, 35/183; P < 0.001). Adenomatous component in flat-type early cancer was less frequent than in polypoid-type cancer (23 percent vs. 92 percent, P < 0.001). The proportion of right-sided colon in flat-type early cancer increased with age (33 percent in patients < or = 59 years, 50 percent in patients between 60 and 69 years, and 72 percent in patients > or = 70 years), whereas polypoid-type early cancer showed minimal change (16 percent, 18 percent, and 25 percent, respectively). An increase in the proportion of right-sided colon with age was also found in advanced cancer (20 percent, 38 percent, and 52 percent, respectively).


CONCLUSIONS
The incidence of flat-type early cancer in right-sided colon increased with age, similar to the pattern of advanced cancer. This suggests that flat-type early cancer may be a precursor of advanced cancer in the right colon, especially in older people.
Okamoto
Makoto
M
Department of Gastroenterology, Faculty of Medicine, University of Tokyo, Tokyo, Japan.
Kawabe
Takao
T
Yamaji
Yutaka
Y
Kato
Jun
J
Ikenoue
Tsuneo
T
Togo
Gouichi
G
Watabe
Hirotsugu
H
Yoshida
Haruhiko
H
Shiratori
Yasushi
Y
Omata
Masao
M
D000236:Adenoma / Q000473:pathology*; D000367:Age Factors; D000368:Aged; D002471:Cell Transformation, Neoplastic; D003111:Colonic Polyps / Q000473:pathology*; D003113:Colonoscopy; D015179:Colorectal Neoplasms / Q000473:pathology*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging