Prognostic evaluation of metallothionein expression in human colorectal neoplasms

To investigate the role of metallothionein in colorectal tumours and the possible relation with other factors associated with tumour progression: expression of cathepsin D (CD), CD44, p53, Rb, bcl-2, c-erbB-2, epidermal growth factor receptor (EGFR), proliferation indices (Ki-67, proliferating cell nuclear antigen (PCNA)), and conventional clinicopathological variables.

The immunohistochemical expression of metallothionein was investigated in 23 cases of colorectal adenoma and 94 adenocarcinomas. Metallothionein expression was examined by the avidinbiotin peroxidase immunoperoxidase (ABC) using the monoclonal mouse antibody E9, on formalin fixed, paraffin embedded tissue.

Positive metallothionein expression (> 5% of neoplastic cells) was observed in 30.4% of adenomas and 25.5% of adenocarcinomas, while 8.7% of adenomas and 14.9% carcinomas showed focal metallothionein positivity. In contrast, 60.9% of adenomas and 59.6% of carcinomas almost completely lacked metallothionein expression. In the series of adenocarcinomas, metallothionein expression was inversely correlated with CD44 in neoplastic cells (p = 0.01). There was no statistically significant difference of metallothionein expression, or the other variables examined, between adenocarcinomas and adenomas.

Metallothionein expression does not seem to indicate aggressive biological behaviour in colorectal adenocarcinomas, in comparison with the other types of carcinoma. The inverse correlation with CD44 could suggest that the decreased metallothionein expression may contribute to the metastatic spread of the lymph node involvement in colorectal cancer. Metallothionein expression does not seem to represent an independent prognostic marker in colorectal cancer.