BACKGROUND. Few studies have focused on the presence and significance of mi
crosatellite instability (MSI) in gastric polyps, and the results on record
are conflicting. The aim of the current study was to address this issue, l
aking into consideration the 2 main types of gastric polyps, the coexistenc
e of foci of malignant transformation, and the expression of p53 and ERBB-2
.
METHODS. Six hyperplastic polyps, 10 adenomatous polyps, and 4 adenomatous
polyps displaying foci of malignant transformation (intestinal-type carcino
ma) were studied for MSI. The authors analyzed a mononucleotide repeal micr
osatellite (BAT-26) and 5 dinucleotide repeats in microdissected formalin f
ixed, paraffin embedded tissue sections that were representative of the les
ions. Expression of p53 and ERBB-2 were evaluated by immunohistochemistry.
RESULTS. BAT-26 positivity was detected in 1 of 6 hyperplastic polyps (16.7
%) and in 2 of 10 adenomas (20%) without malignant transformation. In the 4
adenomatous polyps with carcinomatous foci, BAT-26 positivity was detected
in 2 cases (50%) in both (adenomatous and carcinomatous) components of the
lesions. p53 immunoreactivity was observed in 6 adenomatous polyps, 2 of t
hem with malignant transformation, Overexpression of the ERBB-2 protein was
detected in 1 adenomatous polyp with malignant transformation.
CONCLUSIONS. Replication error (RER+) phenotype occurs in both hyperplastic
and adenomatous polyps of the stomach. The highest frequency is observed i
n adenomatous polyps with carcinomatous foci, suggesting that MSI may play
a role in the process of malignant transformation in this setting. No signi
ficant association was observed between RER+ phenotype and overexpression o
f p53 or ERBB-2 proteins. (C) 1999 American Cancer Society.