Effect of Direct Intra-Tumoral Zinc Injection on PC3 Growth. Prostate cancer cell xenografts were placed into SCID mice and allowed to grow to a size of 300 mm3. Every 48 hours for 14 days, mice were then anesthetized and injected with 200 μL of either saline (black squares) or 3 mM zinc acetate (grey circles). Tumor size was measured at the indicated intervals. Error bars represent average size for 10 mice and "*" represents significance at p < 0.05 by ANOVA.