Dickkopf-1 levels are suppressed in women with breast cancer following zoledronic acid. (A) Dickkopf-1 (DKK-1) levels were measured in women with estrogen receptor (ER)-negative nonmetastatic breast cancer, who received 3-monthly infusions of zoledronic acid (ZOL; n = 6) or placebo (n = 3). DKK-1 levels are presented as mean absolute values and mean percentage of baseline expression. (B) Markers of bone turnover were assessed at the same time points as DKK-1. Values are presented as percentage of baseline expression. (C) Schematic regulation of DKK-1 by mevalonate pathway modulators via inhibition of Cdc42 and Rho. ALP, alkaline phosphatase; CTx, C-terminal telopeptide; IPP, isopentenyl pyrophosphate; TRAP, tartrate-resistant acid phosphatase; PP, pyrophosphate.