Purpose: To investigate the short-term biologic effects of neoadjuvant chemotherapy +/− zoledronic acid (ZOL) in invasive breast cancer.

Experimental Design: Forty patients were randomized to receive a single 4 mg infusion of ZOL 24 hours after the first cycle of FE₁₀₀C chemotherapy, or chemotherapy alone. Randomization was stratified for tumor stage, ER, HER2, and menopausal status. All patients had repeat breast core biopsy at day 5 (D5) ± day 21 (D21). Effects on apoptotic index, proliferation (Ki67), growth index, surrogate serum markers of angiogenesis (VEGF), and serum reproductive hormones within the TGFβ family (activin-A, TGFβ1, inhibin-A, and follistatin) were evaluated and compared.

Results: Baseline clinicopathologic characteristics were well balanced. Cell growth index (increased apoptosis and reduced proliferation) fell at D5 in both groups but recovered more rapidly with chemotherapy + ZOL compared with chemotherapy alone by D21 (P = 0.006). At D5, a greater reduction in serum VEGF occurred with chemotherapy + ZOL compared with chemotherapy: median percentage change −23.8% [interquartile range (IQR): −32.9 to −15.8] versus −8.4% (IQR: −27.3 to +8.9; P = 0.02), but these effects were lost by D21. Postmenopausal women showed a decrease in follistatin levels from baseline in the chemotherapy + ZOL group at D5 and D21, compared with chemotherapy alone (P_interaction = 0.051).

Conclusions: In this pilot study, short-term changes in biomarkers suggest potentially relevant interactions between tumor biology, chemotherapy, modification of the bone microenvironment, and the endocrine status of the host. Larger studies with more frequent dosing of zoledronic acid are needed to assess these complex interactions more thoroughly. Clin Cancer Res; 19(10); 2755–65. ©2013 AACR.