L. Cawkwell et al., Defective hMSH2/hMLH1 protein expression is seen infrequently in ulcerative colitis associated colorectal cancers, GUT, 46(3), 2000, pp. 367-369
Background-Ulcerative colitis is associated with an increased risk of color
ectal cancer above that of the normal population. The relative risk correla
tes with the extent and duration of the disease but the genetic basis of ul
cerative colitis associated cancer risk is not known.
Aims-To assess the prevalence of microsatellite instability and mismatch re
pair gene abnormalities in ulcerative colitis associated colorectal cancer.
Patients-Forty six patients with colorectal cancer, with a previous histolo
gical diagnosis of ulcerative colitis.
Methods-The frequency of microsatellite instability and/or immunohistochemi
cal expression of hMSH2 and hMLH1 was assessed. Thirty three cases were inv
estigated using both approaches.
Results-Although 6/41 (14.6%) cases showed microsatellite instability at on
e or more markers, only one case (2.4%) exhibited high level instability (a
t least two markers affected). Of 38 cases which were assessed using antibo
dies against hMSH2 and hMLH1, only one case (2.6%) showed loss of expressio
n. This case, which showed loss of hMSH2 expression, was the same case whic
h exhibited high level microsatellite instability. The 33 cases which were
investigated using both approaches showed that loss of expression of either
hMSH2 or hMLH1 was not seen in any case which exhibited microsatellite ins
tability in no more than one marker.
Conclusions-This study suggests that both high level microsatellite instabi
lity and loss of expression of hMSH2/hMLH1 are infrequent events in ulcerat
ive colitis associated colorectal cancers. Low level microsatellite instabi
lity was not associated with loss of expression of either hMSH2 or hMLH1.