Breast Cancer with Bone Metastasis: Molecular Insights and Clinical Management.

Despite the remarkable advances in the diagnosis and treatment of breast cancer patients, the presence or development of metastasis remains an incurable condition. Bone is one of the most frequent sites of distant dissemination and negatively impacts on patient's survival and overall frailty. The interplay between tumor cells and the bone microenvironment induces bone destruction and tumor progression. To date, the clinical management of bone metastatic breast cancer encompasses anti-tumor systemic therapies along with bone-targeting agents, aimed at slowing bone resorption to reduce the risk of skeletal-related events. However, their effect on patients' survival remains controversial. Unraveling the biology that governs the interplay between breast neoplastic cells and bone tissue would provide means for the development of new therapeutic agents. This article outlines the state-of-the art in the characterization and targeting the bone metastasis in breast cancer, focusing on the major clinical and translational studies on this clinically relevant topic.

Antiresorptive agents' bone-protective and adjuvant effects in postmenopausal women with early breast cancer.

Potent antiresorptive drugs (bisphosphonate and denosumab) are often used to protect bone health in postmenopausal breast cancer patients. In addition, clinical trials have shown that these drugs increase disease-free survival, though the mechanism of adjuvant benefit is largely unknown. Here we review the bone health and adjuvant data for both classes of antiresorptive drugs and highlight differences in their pharmacology. Inhibition of bone resorption is vitally important to protect against osteoporotic fractures, and may also contribute to adjuvant survival benefits by making the bone microenvironment less amenable to breast cancer metastasis. After a course of therapy, stoppage of bisphosphonates yields a persistent antiresorptive effect, whereas discontinuation of denosumab causes a rebound increase in bone resorption markers and a loss of bone mineral density to baseline levels. Whether the potential adjuvant benefits of denosumab are also rapidly lost after drug discontinuation deserves further investigation.

Proximal Femur Volumetric Bone Mineral Density and Mortality: 13 Years of Follow-Up of the AGES-Reykjavik Study.

Bone mineral density (BMD) has been linked to mortality, but little is known about the independent contribution of each endosteal bone compartment and also the rate of bone loss to risk of mortality. We examined the relationships between (1) baseline trabecular and cortical volumetric BMD (vBMD) at the proximal femur, and (2) the rate of trabecular and cortical bone loss and all-cause mortality in older adults from the AGES-Reykjavik study. The analysis of trabecular and cortical vBMD and mortality was based on the baseline cohort of 4654 participants (aged ≥66 years) with a median follow-up of 9.4 years; the association between rate of bone loss and mortality was based on 2653 participants with bone loss data (median follow-up of 5.6 years). Analyses employed multivariable Cox-proportional models to estimate hazard ratios (HRs) with time-varying fracture status; trabecular and cortical variables were included together in all models. Adjusted for important confounders, Cox models showed that participants in the lowest quartile of trabecular vBMD had an increased risk of mortality compared to participants in other quartiles (HR = 1.12; 95% confidence interval (CI), 1.01 to 1.25); baseline cortical vBMD was not related to mortality (HR = 1.08; 95% CI, 0.97 to 1.20). After adjustment for time-dependent fracture status, results were attenuated and not statistically significant. A faster loss (quartile 1 versus quartiles 2-4) in both trabecular and cortical bone was associated with higher mortality risk (HR = 1.37 and 1.33, respectively); these associations were independent of major potential confounders including time-dependent incident fractures (HR = 1.32 and 1.34, respectively). Overall, data suggest that faster bone losses over time in both the trabecular and cortical bone compartments are associated with mortality risk and that measurements of change in bone health may be more informative than single-point measurements in explaining mortality differences in older adults. © 2017 American Society for Bone and Mineral Research.

Comparative effectiveness on survival of zoledronic acid versus pamidronate in multiple myeloma.

Zoledronic acid and pamidronate are the two bisphosphonates approved in the United States to reduce multiple myeloma skeletal complications. Little prior evidence exists comparing survival outcomes between the two. We evaluated the incidence of skeletal-related events and overall survival in patients with myeloma treated with zoledronic acid versus pamidronate using a cohort of 1018 United States veterans. At a median follow-up of 26.9 months, patients receiving zoledronic acid had a 22% reduction in risk of death compared to pamidronate (hazard ratio 0.78; 95% confidence interval, 0.67-0.92). The benefit persisted after controlling for potential confounders. Adjusted Cox modeling with inverse probability weighting and propensity score matching supported these findings. Zoledronic acid was also associated with a 25% decrease in skeletal-related events. Zoledronic acid is associated with increased overall survival and decreased skeletal-related events compared to pamidronate in patients with multiple myeloma and should become the preferred bisphosphonate.

Effects of surface microtopography on the assembly of the osteoclast resorption apparatus.

Bone degradation by osteoclasts depends on the formation of a sealing zone, composed of an interlinked network of podosomes, which delimits the degradation lacuna into which osteoclasts secrete acid and proteolytic enzymes. For resorption to occur, the sealing zone must be coherent and stable for extended periods of time. Using titanium roughness gradients ranging from 1 to 4.5 µm R(a) as substrates for osteoclast adhesion, we show that microtopographic obstacles of a length scale well beyond the range of the 'footprint' of an individual podosome can slow down sealing-zone expansion. A clear inverse correlation was found between ring stability, structural integrity and sealing-zone translocation rate. Direct live-cell microscopy indicated that the expansion of the sealing zone is locally arrested by steep, three-dimensional 'ridge-like barriers', running parallel to its perimeter. It was, however, also evident that the sealing zone can bypass such obstacles, if pulled by neighbouring regions, extending through flanking, obstacle-free areas. We propose that sealing-zone dynamics, while being locally regulated by surface roughness, are globally integrated via the associated actin cytoskeleton. The effect of substrate roughness on osteoclast behaviour is significant in relation to osteoclast function under physiological and pathological conditions, and may constitute an important consideration in the design of advanced bone replacements.

Prophylactic use of zoledronic acid to prevent early bone loss is safe and feasible in patients with acute myeloid leukemia undergoing allogeneic stem cell transplantation.

Osteopenia and osteoporosis are well-known consequences of allogeneic stem cell transplantation (allo-SCT). The role of prophylactic zoledronic acid on bone turnover following allo-SCT has not been well characterized. We prospectively studied the role of prophylactic use of zoledronic acid on bone metabolism in 17 patients with acute myeloid leukemia (AML) undergoing allo-SCT over a period of three yr (2006-2009). We measured bone mineral density using dual energy X-ray absorptiometry (DXA) scanning and the markers of bone turnover by urinary N-terminal telopeptide (uNTX) and serum osteocalcin levels prior to and serially following transplantation. All patients received 4 mg of zoledronic acid (Zometa, Novartis Pharmaceuticals Corp., Basel, Switzerland) intravenously prior to starting conditioning regimen and at six months after SCT. DXA scores did not change significantly in any patient over time (p > 0.05). uNTX progressively decreased over time (p < 0.001) and serum osteocalcin stabilized after six months. No patient developed osteonecrosis of the jaw. In conclusion, in this prospective pilot study, prophylactic use of zoledronic acid to prevent early bone loss was found to be safe and feasible in patients with AML undergoing allo-SCT during the immediate post-transplantation period.

Bone deposition, bone resorption, and osteosarcoma.

Bone deposition and bone resorption are ongoing dynamic processes, constituting bone remodeling. Some bone tumors, such as osteosarcoma (OS), stimulate focal bone deposition. OS is the most common primary bone tumor in children and young adults. A complex network of genes regulates bone remodeling and alterations in its expression levels can influence the genesis and progression of bone diseases, including OS. We hypothesized that the expression profiles of bone remodeling regulator genes would be correlated with OS biology and clinical features. We used real-time PCR to evaluate the mRNA levels of the tartrate-resistant acid phosphatase (ACP5), colony stimulating factor-1 (CSF1R), bone morphogenetic protein 7 (BMP7), collagen, type XI, alpha 2 (COL11A2), and protein tyrosine phosphatases zeta 1 (PTPRZ1) genes, in 30 OS tumor samples and correlated with clinical and histological data. All genes analyzed, except CSF1R, were differentially expressed when compared with normal bone expression profiles. In our results, OS patients with high levels of COL11A2 mRNA showed worse overall (p = 0.041) and event free survival (p = 0.037). Also, a trend for better overall survival was observed in patients with samples showing higher expression of BMP7 (p = 0.067). COL11A2 overexpression and BMP7 underexpression could collaborate to OS tumor growth, through its central role in bone remodeling process.

Advances in multiple myeloma and spine disease.

Progressive bone destruction is the hallmark of multiple myeloma (MM) and is responsible for principal morbidity in the disease. The spine is the most afflicted skeletal organ, and vertebral fractures have significantly contributed to its poor prognosis. The principal underlying pathologic mechanism causing bone disease in MM is a shift in the balance of bone formation and bone resorption toward bone resorption, and eventually total dissociation between the 2 processes occurs in latter stages of the disease. During the past decade bisphosphonates have become an important adjunctive treatment in the management of MM, in which they have shown the ability to reduce bony complications associated with the disease. Advances in minimally invasive surgical techniques, such as percutaneous vertebroplasty and kyphoplasty, offer these patients less-invasive options for the treatment of vertebral collapse and restoration of their normal function. This report reviews recent advances in the understanding of bone disease in MM, the role of bisphosphonates in the prevention of skeletal events, and available data regarding percutaneous vertebroplasty and kyphoplasty.

Extended survival in advanced-stage multiple myeloma patients treated with gallium nitrate.

Adjunctive anti-bone resorption therapy has become an important part of multiple myeloma (MM) treatment. Currently, no definite evidence exists that this therapy increases survival. We examined a cohort of 13 of 167 patients (8%) treated with the M-2 protocol who received adjuvant gallium nitrate (GN) treatment for osteolysis, and then compared the outcome of these patients to all individuals treated with the M-2 regimen. The stage at diagnosis was IA in two patients, IIIA in 10 patients and IIIB in one. Median age at diagnosis was 51 years (range 35-73). Median (range) of entry data were: paraprotein level: 6000mg/dl (3058-8675); beta2M: 2.7mg/l, (1.2-9.6); LDH: 166U/l (142-237); hemoglobin: 10.2 g/dl (8.3-12.6); albumin: 3.7 g/dl (2.5-5.0); calcium: 10.0 mg/dl (8.3-14.5); creatinine: 1.2 mg/dl (0.7-2.7). Median survival in these patients was 87+ months from time of diagnosis compared with 48 months for all other patients treated on the M-2 protocol. We identified a subgroup of patients with remarkably prolonged survival who had received M-2 chemotherapy and GN. Survival in this group markedly exceeds expectations for patients with advanced stage disease and poor prognostic features. The administration of GN may have a positive impact on survival either by decreasing skeletal complications or through a direct action of GN on the complex cytokine network involved in the proliferation of the malignant myeloma cell.