Quantification of cathepsin D in plasma of patients with malignant melanoma

The high mortality rate of melanoma patients who develop metastases prompted us to seek for a prognostic soluble marker to identify high-risk and non-risk patients at the stage of the primary tumour. Therefore, we developed a new ELISA for quantifying plasma concentrations of the proteolytic enzyme cathepsin D (CD) in patients with primary tumours (MM-P) and with metastases (MM-M), respectively, compared to a control group. Whereas healthy probands (n = 56) and MM-P (n = 68) showed similar mean values of CD (0.73 +/- 0.45 ng/ml and 0.82 + 0.80 ng/ml), MM-M (n = 40) yielded significantly reduced plasma levels (0.43 +/- 0.53 ng/ml) revealing a high significant discrimination both between controls and MM-M, and MM-P and MM-M (p < 0.0001). From the beginning of the study (1990) to the present 11 of 68 MM-P developed metastases. In order to test the prognostic efficiency of this enzyme to determine those patients at high-risk and non-risk for developing metastases, the receiver operating characteristic analysis was used showing that CD plasma levels cannot supply reliable prognostic values (W = 0.53, p = 0.66).