The possible different roles of denosumab in prevention and cure breast cancer bone metastases: A 'hypothesis-generator' study from clinical practice

The most frequent site of recurrence in breast cancer (BC) is the bone, particularly in patients with 'luminal-like' disease. Denosumab has been shown to prevent aromatase inhibitors (AIs) induced bone resorption in postmenopausal early BC patients and reduce skeletal-related events (SREs) in bone metastatic breast cancer (BMBC). A 'real life' analysis of 90 BMBC patients treated with denosumab was performed. Eighty-six patients (95.6%) had 'luminal-like' disease, 72 (80%) had bone metastases at the time of first recurrence of disease. Among 50 patients with metachronous 'luminal-like' disease, 40 (80%) had first recurrence to the bone. Among these patients median time to skeletal recurrence (TSkR) was shorter for patients who were previously exposed to AIs compared to those who were not (53.0 vs. 102.0 months, respectively; P=0.0300) and longer for patients previously treated with tamoxifen compared to those who were not (102.0 vs. 59.0 months, respectively; P=0.0466). Both of them were not confirmed at multivariate analysis. In the overall population, 17 first SREs were observed (16 radiation therapy) and median time to first SRE was not reached. A statistically significant difference in the incidence of SREs was detected only between patients with exclusively osteolytic bone metastases vs. those without (P=0.013). The presence of exclusively-osteolytic bone metastases was the only factor significantly associated with a shorter time to first SRE (P=0.011). The only G3 toxicity reported was hypocalcemia in one patient. No osteonecrosis of the jaw events (ONJ) occurred. This study demonstrated that a pro-active attitude enables the treatment of the majority of patients with denosumab without significant class-related toxicities. The majority of SREs were from radiation therapy, so pain still remains the clinical hallmark of bone metastases, particularly for osteolytic ones. The suggestion that estrogen deprivation with AIs can favor a 'bone-related' risk conditions for developing bone metastases must be considered with caution and surely needs further validations.