L. Cawkwell et al., Choice of management strategy for colorectal cancer based on a diagnostic immunohistochemical test for defective mismatch repair, GUT, 45(3), 1999, pp. 409-415
Background-Despite intensive research into the molecular abnormalities asso
ciated with colorectal cancer (CRC), no diagnostic tests have emerged which
usefully complement standard histopathological assessments.
Aims-To assess the feasibility of using immunohistochemistry to detect repl
ication error (RER) positive CRCs and determine the incidence of RER positi
vity within distinct patient subgroups.
Methods-502 CRCs were analysed for RER positivity (at least two markers aff
ected) and/or expression of hMSH2 and hMLH1.
Results-There were 15/30 (50%) patients with metachronous CRCs, 16/51 (31%)
with synchronous CRCs, 14/45 (31%) with a proximal colon carcinoma, and 4/
23 University of Leeds, (17%) who developed a CRC under the age of 50 showe
d RER positivity. However, 0/54 patients who developed a solitary carcinoma
of the rectum/left colon over the age of 50 showed RER positivity. Immunoh
istochemical analysis revealed that 66/66 (100%) RER positive carcinomas we
re associated with complete lack of expression of either hMSH2 or hMLH1. Th
is correlation was confirmed using a further 101 proximal colon carcinomas.
Patients with a mismatch repair defective carcinoma showed improved surviv
al but a 5.54 times relative risk of developing a metachronous CRC. A prosp
ective immunohistochemical study revealed 13/117 (11%) patients had a misma
tch repair defective carcinoma. A fivefold excess of hMLH1 defective cases
was noted.
Conclusions-Ah RER positive carcinomas were identified by the immunohistoch
emical test. This is the first simple laboratory test which can be performe
d routinely on all CRCs. It will provide a method for selecting patients wh
o should be investigated for HNPCC, offered long term follow up, and who ma
y not respond to standard chemotherapy regimens.