Evaluation of cystatin C mRNA and protein expression showed no significant changes between human premalignant and malignant cells (brain, pituitary [77], renal carcinoma [78], breast [79], and colon cancers [80]), but a high level of cystatin C in the serum, the pleural effusions, and the ascites fluids collected from cancer patients was observed [81,82]. This evidence concerns the gene CST3 and cancer.