Intestinal M3 antigen, A marker for the intestinal‐type differentiation of gastric carcinomas

The mucus‐associated intestinal M3 antigen, normally restricted to intestinal goblet cells, was found in 35 out of 100 gastric adenocarcinomas belonging to intestinal (19/64) as well as diffuse (16/36) types according to Laurén's classification, often accompanying the other mucus‐associated gastric Ml and M2 antigens. This M3 antigen was predominant over the gastric M antigens in 25 of these 35 tumors; 18 of these belonged to the histological intestinal type. According to the WHO classification, the M3 antigen was found to predominate in all mucinous adenocarcinomas (7/7), was never present in the undifferentiated carcinomas (0/8), but was also found in some tubulo‐papillar (16/57) and signet‐ring cell (12/27) adenocarcinomas. This antigen could be used as a new criterion and incorporated into a point system containing morphological and tumor cell behavioral considerations; then it would appear to be a good marker for intestinal‐type differentiation. Indeed, 22 of these 25 gastric adenocarcinomas which produced predominantly M3 antigen showed such an intestinal‐like differentiation. The M antigenic pattern of gastric carcinoma suggested a duodenal rather than colonic‐type differentiation.