CST4 and prostate cancer: Low cystatin level or loss of cystatin function is often associated with poor prognosis, as it can signal increased proteolytic activity, higher invasiveness, and metastatic potential.29 Studies have shown that in cancers, such as breast and prostate cancer, lower cystatin expression correlates with advanced stage, higher metastatic burden, and shorter survival.30 On the other hand, high levels of cystatins may be associated with less aggressive tumors and better outcomes as they counteract protease-driven processes that favor metastasis.23,31