Cathepsin-d in breast carcinomas - the role of the stromal cell component

Cathepsin D was initially identified as being an oestrogen responsive protein in breast cancer cell lines. Subsequent studies have shown a role for this lysosomal enzyme in invasion and metastasis. Immunoassay and blotting studies have demonstrated a relationship between high cathepsin D levels in breast carcinomas and poor prognosis, but the converse or no relationship has been found in immunohistochemical studies. Cathepsin D from stromal cells, which will be included in tumour homogenates, may account for this difference. This immunohistochemical study of 145 breast carcinomas has used two monoclonal antibodies to cathepsin D, and considered staining of stromal cells as well as tumour cells. Some differences were found in the reactivities of the two antibodies. No relationship has been found between tumour cell reactivity and node status, grade, oestrogen receptor status and prognosis. Up to one third of carcinomas had no staining of tumour cells but a diffuse stromal cell infiltrate. Prominent stromal cell reactivity was associated with poorer survival but these tumours were predominantly poorly differentiated. However, stromal cell reactivity cannot account alone for the differences reported between different studies in relation to cathepsin D land prognosis. Other factors may include differences in detection of the different molecular weight forms, as well as quantification.