['It was the aim of this study to evaluate the serum levels of cathepsin D (Cath D) as a diagnostic tool in patients with renal cell carcinoma (RCC) in comparison with healthy volunteers.', 'Cath D serum levels were measured in serum samples obtained preoperatively from 32 patients with histologically confirmed RCC versus 30 healthy individuals using an enzyme immunoassay. Additionally, for the tumor group, Cath D serum levels were correlated with tumor stage and grade as determined according to the 2002 TNM classification.', 'The serum Cath D concentration was not significantly different in patients with RCC compared with healthy individuals (mean 16.58 vs. 16.64 ng/ml; p = 0.43). Furthermore, there was no significant association between Cath D serum levels and several patient or tumor characteristics such as tumor stage, tumor grade, lymph node status, presence of metastasis, gender or age.'] Are cathepsin D serum levels a valid serum marker in renal cell carcinoma?