Cathepsin X is a cysteine protease involved in mechanisms of malignant progression. It is secreted from tumour cells as a proenzyme and may serve to predict the disease status and risk of death for cancer patients. In a previous, pilot, study on 77 colorectal patients we demonstrated the correlation of higher serum levels with shorter overall survival.

264 patients with colorectal cancer were included in a prospectively accrued multi-centre observational cohort study with the aim of testing novel biomarkers. Blood samples were collected before preoperative large bowel endoscopy and total cathepsin X was measured in sera by ELISA. As a control group we selected at random 77 subjects who had no findings at endoscopy and reported no co-morbidity.

The mean level of cathepsin X in cancer patients did not differ from the control levels (23.4 ng/ml ± 6.4 SD vs. 18.8 ng/ml ± 11.4 SD, p > 0.05) and there was no association with age, gender, disease stage, tumour location or CEA. In univariate analysis no association between cathepsin X levels and overall survival was demonstrated for the entire set of patients, however, cathepsin X was associated with survival in a group of patients with local resectable disease (stages I-III) (HR = 1.69, 95% CI: 1.03-2.75, p = 0.03). For this group, multivariate Cox regression analysis showed an association (HR = 3.13, 95% CI: 1.37-7.18, p = 0.003) between high cathepsin X levels and shorter overall survival for patients who did not receive chemotherapy, whereas, for patients who received chemotherapy, there was no association between cathepsin X and survival (HR = 0.51, 95% CI: 0.20-1.33, p = 0.88).