Immunostaining of cathepsin D in breast cancer: quantification by computerised image analysis and correlation with cytosolic assay.

Cathepsin-D (cath-D) was quantified in 34 breast cancer specimens by immunohistochemical staining of frozen sections with a computer image analysis and the results were compared with the corresponding cytosolic assay. Cath-D concentrations varied from 0 to 420 arbitrary units (AU). Tumour cells were more intensely stained than peritumoral tissue with the D7E3 mouse monoclonal antibody than with rabbit polyclonal antibodies. There was a good correlation (r = 0.80) between cath-D values obtained either by immunohistochemistry with D7E3 antibody or by cytosolic immunoenzymatic assay. However, with a cut-off of 50 AU, 3 out of 25 patients had higher immunohistochemical values and 2 had higher cytosolic values. Therefore, quantification of cath-D concentration in tissue section by immunostaining and a computerised image analyser, which is the only technique available for small tumours, should provide similar prognostic information to that obtained by assaying cath-D in the cytosol.