Immunohistochemical metallothionein expression in colorectal adenocarcinoma: correlation with tumour stage and patient survival

Metallothioneins (MTs), a set of ubiquitous low-molecular-weight proteins essential for the protection of cells against heavy metal ion toxicity, were demonstrated immunohistochemically using a monoclonal antibody (E9) against a conserved epitope of I and II isoforms in a series of 109 colorectal adenocarcinomas. In a semiquantitative analysis strong MT expression in the majority of tumour cells was observed in 34 (31%) cases, 24 (22%) tumours showed a focal MT positivity, and 51 (47%) almost completely lacked MT expression. These differences in MT expression were statistically significantly (P<0.05) associated with the tumour stage (Dukes classification) and the lymph node involvement at the time of operation (pN stages). However, in contrast to previous findings obtained on a variety of tumours, MT positivity was associated with a favourable clinical outcome in colonic carcinoma, which may indicate their different biological behaviour. Survival curves of cases with MT-positive and MT-negative status differed from each other in a univariate analysis (Mantel-Haenszel: 8.9, P<0.05) but lost significance when a multivariate analysis was carried out by means of the Cox proportional regression model with Dukes' stages as a stratification factor. It is concluded that immunohistochemically demonstrated MT expression is significantly associated with tumour stages but does not represent an independent prognostic variable in colorectal cancer. However, it may provide important information about some of the biological mechanisms underlying progression in colorectal cancer.