Utility of cystatin C as a potential bladder tumour biomarker confirmed by surface plasmon resonance technique.

Background & objectives: The determination of cystatin C (cysC) may be helpful in diagnosis and monitoring of cancer because the pathogenesis of cancer is linked with an increased activity of cysteine peptidases (cathepsins) and a decrease of cysC concentration. This study was aimed to examine the utility of cysC as a marker of bladder cancer (BCa) to be used in the diagnosis.

Methods: This study was conducted with 90 patients with BCa and 27 healthy people. Patients with other cancers, inflammation process and impaired renal function were excluded from the study. The concentrations of cysC in the plasma and urine were measured by surface plasmon resonance imaging technique.

Results: The concentration of cysC in the serum taken from the patients with BCa [0.35±0.02 μg/ml (range: 0.20-0.78 μg/ml)] was significantly (P<0.001) lower than the serum cysC concentration of the healthy people [0.68±0.05 μg/ml (range: 0.52-0.89 μg/ml)]. The urinary cysC concentration of the BCa patients [0.19±0.01 μg/ml (range: 0.09-0.34 μg/ml)] was not significantly different from the urinary cysC concentration of the healthy people [0.24±0.02 μg/ml (range: 0.16-0.33 μg/ml)]. Receiver operating characteristic (ROC) curve showed that BCa patients with cysC concentration <0.54 μg/ml [sensitivity: 87%; specificity: 92%; area under the curve (AUC) of ROC: 0.927; P=0.02] could be optimally separated from healthy people. The ROC curve further showed that superficial low-grade patients with cysC concentration lower than 0.36 μg/ml (sensitivity: 0.63%; specificity: 0.58%; AUC of ROC: 0.635; P=0.08) could not be optimally separated from high-risk tumour patients.

Interpretation & conclusions: BCa patients have lower serum cysC concentration than the control group. Serum cysC may be considered as a potential marker of BCa but not its aggressiveness.