In general, the change in serum protease inhibitor cystatin B was milder (Fig. 2) as compared to CA-125 and procathepsin B. Moreover, serum cystatin B level had a tendency to increase (p<0.05 vs. serum in the control group) only in ovarian cancer, not in benign ovarian tumours (Fig. 2). This evidence concerns the gene MUC16 and ovarian cancer.