Recent evidences suggest that zoledronate, one of the most used bisphosphonates (BPs) in the clinical setting for the prevention and treatment of bone metastasis in cancer patients, may have antitumor activity in early breast cancer. Notwithstanding some conflicting data, the majority of the clinical trials have shown some positive effects of BPs on patients outcome, reporting improved Disease Free Survival (DFS) and Overall Survival in mostly chemotherapy-naive premenopausal patients after a 3-year treatment with zoledronate and better DFS for immediate use of zoledronate in postmenopausal patients receiving adjuvant aromatase inhibitor treatment. Moreover, early breast cancer patients treated with neoadjuvant chemotherapy in combination with zoledronic acid showed better response compared with chemotherapy alone.

Even though different explanations have been proposed over-time, the exact mechanism of action of the anti-tumor activity of BPs is still not well understood. Basically, BPs are mevalonate pathway inhibitors and one of the most intriguing hypothesis supporting their anticancer activity relies on the modulation of the mevalonate downstream metabolism. Biologically active mevalonate metabolites are involved in tumour cell proliferation, survival, invasion and metastasis. Moreover, there is evidence that selected cancer subtypes may present a more pronounced mevalonate activity, able of maintaining an aggressive phenotype. Indeed, the mevalonate pathway has deep impact on the function of YAP/TAZ, transcriptional regulators of tumour growth. Preclinical evidences, suggest that BPs are able to interfere with YAP/TAZ expression, via mevalonate pathway. This study addresses the clinical role of BPs in triple negative breast cancer (TNBC) patients selected by the level of mevalonate pathway regulation, namely the p53 expression.

This study is a multicenter single-arm, phase II study primarily aimed at assessing the anti-tumor activity of pre-operative zoledronate measured through its effect on the Ki67 proliferative surrogate biomarker, in patients with TNBC classified according to the p53 expression (high vs low p53 expression). An high level of p53 is defined by IHC expression ≥30%, while a low level is defined by IHC expression \<30%, as previously described. Patients with newly diagnosed, untreated, operable TNBC, intended to definitive breast surgery and suitable for pre-operative therapy will be registered using a centralized system and will receive a pre-operative, single administration of zoledronate (4mg i.v.), 7 days before definitive breast surgery . Ki67 levels will be assessed in core biopsy tumor samples collected at the time of diagnosis and after zoledronate treatment at the time of definitive surgery. Primary endpoint of the study is the proportion of responder patients, defined as those with at least 30% reduction in Ki67 at surgery with respect to core-biopsy analysis. The secondary objective of the study is to investigate the effect of zoledronate on critical genes/proteins related to p53 and mevalonate pathways, p53/PIN1 and YAP/TAZ, analyzed in the tumor tissue at the time of diagnosis (core biopsy) and at definitive surgery. The safety profile of zoledronate will be evaluated by the National Cancer Institute-Common Terminology Criteria for Adverse Events (NCI-CTCAE) scale, version 4.0 and by the occurrence of serious adverse reactions. The total number of patients required is forty. The overall duration of the project is expected to be 32 months, divided as follows: 30 months for accrual, followed by 2 months of follow-up after the recruitment of the last patient, aimed to collect data on zoledronate safety and tolerability. The primary analysis will be conducted on the PP population which will include all patients registered, who received the dose of study treatment and underwent definitive breast surgery, with no major violations of the eligibility criteria or during study conduction. Proportion of responder patients, defined as those with at least 30% reduction in Ki67 at surgery with respect to core-biopsy analysis, will be presented as point estimate and 95% confidence intervals (95% CIs) for each group. Logistic regression techniques will be used to compare groups in univariate and multivariate model adjusted for ECOG-PS, sex and pre- and postmenopausal status. The results of this project may eventually contribute to unveil novel anticancer mechanism of action of BPs and new therapeutic options for triple negative breast cancer.