PCNA and breast cancer: Similarly, it has been observed that low doses of BBR can sensitize breast cancer cells lines to CDDP, positively regulating caspases 3 and 9, negatively regulating the expression of the Bcl-2 protein and, most importantly, increasing the DNA damage caused by CDDP while reducing the level of cellular PCNA (Proliferating Cell Nuclear Antigen) [48].