C3 and breast cancer: We combined the unique abilities of EPI-X4 peptides targeting the CXCR4 receptor on BC cells [8] and of the enzyme C3bot1 from the bacterium Clostridium (C.)botulinum (abbreviated as C3), which specifically inhibits Rho, a master-regulator of the actin cytoskeleton that is crucial for both tumor growth and osteoclast formation and activity [9,10,11].