Immunohistochemically demonstrated metallothionein expression in malignant melanoma

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Abstract
Metallothioneins are ubiquitous proteins with a high affinity for heavy metal ions, e.g. zinc, copper and cadmium. Experimentally, metallothionein over‐expression in cell lines derived from a variety of cancers has been associated with resistance to anticancer drugs and irradiation therapy. Using a monoclonal antibody (E9) to metallothionein we investigated immunoreactive expression in routinely fixed and paraffin‐embedded tissue from 63 cases of malignant melanoma and 13 secondary deposits. Whereas a variety of cells in normal skin showed metallothionein expression, all forms of benign naevi studied were uniformly negative. In contrast 13/30 ‘thin’ (≤1.5 mm; 0.7 ± 0.4). 25 29 ‘thick’ malignant melanoma (> 1.5 mm; 5.5 ± 3.9) and 12/13 metastases were positive. Six patients with thin and 19 with thick melanoma with metallothionein expression died during a mean observation period of 6.4 ± 1.8 and 3.6 ± 2.5 years, respectively, their survival distribution function analyses giving statistically significant results for both the vertical tumour thickness (P < 0.0001) and metallothionein expression (P < 0.0001). These immunohistochemical results, based on routinely processed paraffin‐embedded tissue, suggest that metallothionein expression in malignant melanoma is significantly associated with progressive disease and might therefore be a useful prognostic indicator.