Preoperative
bevacizumab and
chemotherapy may benefit a subset of
breast cancer (BC) patients. To explore potential mechanisms of this benefit, we conducted a phase II study of neoadjuvant
bevacizumab (single dose) followed by combined
bevacizumab and
adriamycin/
cyclophosphamide/
paclitaxel chemotherapy in HER2-negative BC. The regimen was well-tolerated and showed a higher rate of
pathologic complete response (pCR) in triple-negative (TN)BC (11/21 patients or 52%, [95% confidence interval (CI): 30,74]) than in
hormone receptor-positive (HR)BC [5/78 patients or 6% (95%CI: 2,14)]. Within the HRBCs, basal-like subtype was significantly associated with pCR (P = 0.007; Fisher exact test). We assessed interstitial fluid pressure (IFP) and tissue biopsies before and after
bevacizumab monotherapy and circulating plasma
biomarkers at baseline and before and after combination
therapy.
Bevacizumab alone lowered IFP, but to a smaller extent than previously observed in other
tumor types. Pathologic response to
therapy correlated with sVEGFR1 postbevacizumab alone in TNBC (Spearman correlation 0.610, P = 0.0033) and pretreatment microvascular density (MVD) in all patients (Spearman correlation 0.465, P = 0.0005). Moreover, increased pericyte-covered MVD, a marker of extent of vascular normalization, after
bevacizumab monotherapy was associated with improved pathologic response to treatment, especially in patients with a high pretreatment MVD. These data suggest that
bevacizumab prunes vessels while normalizing those remaining, and thus is beneficial only when sufficient numbers of vessels are initially present. This study implicates pretreatment MVD as a potential predictive
biomarker of response to
bevacizumab in BC and suggests that new
therapies are needed to normalize vessels without pruning.