Adenoma and Adenocarcinoma of the Small Intestine

Differential Diagnosis

Because of the rarity of small intestinal carcinomas, most questionable cases should be considered colorectal

Reports from Chen and Zhang suggest that immunohistologic stains may be useful:

Note that the opposite result is not always discriminatory; see Special Studies for complete staining results

Misplaced glands in a Peutz-Jeghers polyp must always be ruled out, especially in a young patient or a cytologically bland tumor

Peutz-Jeghers Polyp with Misplaced Glands	Small Intestinal Adenocarcinoma
Overlying typical hamartomatous polyp	Overlying adenoma may be present
Usually cytologically bland	Usually cytologically malignant
Glands may permeate muscle but no desmoplastic response	Desmoplastic response usually present
Lamina propria may be retained around entrapped glands	No retained lamina propria around infiltrating glands
Glands frequently have a mixed population of cell types - mucus, goblet, paneth cells	Monomorphic population

Expression of MUC1 or MUC5AC has been suggested as favoring carcinoma over normal small intestinal mucosa (Zhang 2007)

One report, however, describes basal staining of normal mucosa with MUC1 (Matsubayashi)
MUC5AC stains normal goblet cells and gastric metaplasia
Ultimately, the diagnosis of carcinoma must be made on morphologic grounds