Cathepsin D is a protease involved in the metastasis and angiogenesis of mammary carcinomas. This review analyzes the significance of the tumor protease cathepsin D in mammary carcinomas as a tumor marker. We present a systematic overview based on a selective Medline search. Cathepsin D is expressed in mammary carcinomas and exhibits higher expression in invasive ductal carcinomas compared with lobular carcinomas. Nodal positive carcinomas showed reduced cathepsin D expression compared to lymph node metastases, and increased expression has been observed in hormone-receptor negative tumors. Thus, the expression of cathepsin varies between the two histological types. Increased cathepsin-D expression in acinar affection has also been described. The lack of an association of cathepsin D with known prognostic factors such as CA15-3, ERalpha and ERbeta does not prevent it from being using as a tumor marker. Cathepsin has already been used along with other genes as a prognostic parameter for carcinoma patients in gene arrays.