The occurrence of predominant histologic phenotypes in event colonic c
arcinomas from two disparate geographical regions were analyzed. A tot
al of 424 overt colonic carcinomas (223 in Swedish and 201 in Japanese
patients) were classified into predominant phenotypes (i.e. comprisin
g >50% of the tumor). Six predominant phenotypes were found: tubular,
serrated-microcystic villous, fenestrated, signet ring cell and undiff
erentiated. A predominant phenotype was present in 57.3% (n=243) of th
e 424 tumors (in 55.2% of the 223 tumors from Swedish patients and in
61.7% of the 201 tumors from Japanese patients). The serrated -microgl
andular phenotype was significantly more frequent in Japanese than in
Swedish patients. Environmental and/or ethnic factors may be the possi
ble cause(s) for that difference. The frequency of regional lymph node
tumor spread (Dukes C) was significantly lower in serrated-microgland
ular and in villous phenotypes than in undifferentiated-signet ring ce
ll types, despite that patients harbouring either one of the two forme
r phenotypes were among the oldest in the whole series. Serrated-micro
glandular and villous colonic cancer phenotypes may carry a better pro
gnosis (independently of their degree of histologic differentiation or
age) since they are less prone to metastasize to regional lymph nodes
than undifferentiated-signet ring cell phenotypes.