Immunohistochemical demonstration of metallothionein in eyes with choroidal melanomas

The since immunohistochemically detectable metallothionein (MT) overexpression has been described in a variety of human tumours, including skin melanomas, in relation to different stages of tumour development and progression.

We used a monoclonal antibody to investigate the distribution of MT in 18 formalin-fixed, paraffin-embedded, surgically enucleated eyes with choroidal melanomas, from 18 patients (8 male, 10 female; age range 30-83 years, mean 58.7). Clinico-pathological details and follow-up data (2-124 months, mean 36.1) were also available. MT immunoreactivity was recorded and the percentage of stained cells was graded for semiquantitative purposes. Correlations between immunohistochemical data and morphological characteristics of melanomas were investigated using non-parametric methods; survival analysis was done by the Kaplan-Meier method and the survival curves were compared by the Mantel-Cox log-rank test.

MT immunoexpression was found in 15/18 cases (83.3%) with staining scores from 1 to 3; MT staining varied in intensity and was mainly localized in the cytoplasm, although a combined nuclear/cytoplasmic reactive pattern was seen in neoplastic elements. No differences in MT immunostaining were seen in relation to age or sex, tumour size, histotype and amount of pigment; univariate analysis of survival data showed no prognostic significance regarding MT expression.

The immunohistochemical evidence of MT in neoplastic elements could be related to the production of this scavenging protein in the tumour for cell defense mechanisms against hydroxyl free radicals, and to act as a Zn donor, since Zn is required for the synthesis of DNA and DNA-repair enzymes.