Localization of metallothionein in breast carcinomas. An immunohistochemical study

Metallothionein (MT) is a cysteine-rich, low molecular weight protein that binds zinc, copper, and cadmium. It is present in a number of normal cells including hepatocytes particularly during fetal and early postnatal life. It has been suggested that developmental profile of MT is similar to other oncofetal gene products and hence, it could be used as a marker for aggressive tumour behaviour. In order to test that hypothesis, we used a monoclonal antibody to MT and immunohistochemically evaluated formalin-fixed, paraffin-embedded tissues from 79 breast carcinomas. In non-neoplastic breast tissue, a strong nuclear and cytoplasmic staining was observed in myoepithelial cells. Positive staining for MT was present in 35 (44%) of breast carcinomas. In most positive cases, nuclear, or both nuclear and cytoplasmic staining was seen. All positive tumours were invasive ductal carcinomas, including a medullary and a metaplastic carcinoma. None of the mucinous, lobular, or intraductal papillary carcinomas reacted for MT. A statistically significant association was found between MT immunostaining and histological grade (P < 0.01) as well as with nuclear grade (P < 0.01). We also observed an inverse relationship between MT staining and oestrogen receptor content of tumours (P < 0.01). Similarly, a statistically significant association was found between moderate and strong MT immunostaining and decreased overall survival and shorter disease-free survival (P < 0.01). MT immunostaining was also predictive of a worse prognosis in the subgroup of lymph node negative (P < 0.001) and oestrogen receptor negative patients (P < 0.01). No statistically significant association was found between MT staining and size of tumour or the presence of lymph node metastasis. We conclude that MT staining may be a useful marker of less differentiated and more aggressive carcinomas of the breast.