Clinical review 165: Markers of bone remodeling in metastatic bone disease

A Phase I/II Clinical Trial of Pembrolizumab and Cabozantinib in Metastatic Renal Cell Carcinoma

Purpose

Immune checkpoint inhibitor and VEGFR inhibitor combinations are effective treatments for patients with metastatic renal cell carcinoma (mRCC). This phase I/II clinical trial evaluated the safety and efficacy of pembrolizumab and cabozantinib in patients with mRCC.

Experimental Design

Eligible patients had mRCC with clear-cell or non-clear cell histology, adequate organ function, Eastern Cooperative Oncology Group 0-1 performance status, and no prior exposure to pembrolizumab or cabozantinib. The primary endpoint was objective response rate (ORR) at the recommended phase II dose (RP2D). Secondary endpoints included safety, disease control rate (DCR), duration of response (DoR), progression-free survival (PFS), and overall survival (OS).

Results

Forty-five patients were enrolled. A total of 40 patients were treated at the RP2D of pembrolizumab 200 mg i.v. every 3 weeks and cabozantinib 60 mg orally once daily, 38 of which were evaluable for response. The ORR was 65.8% [95% confidence interval (CI), 49.9-78.8] for all evaluable patients [78.6% as first-line therapy, 58.3% as second-line therapy]. The DCR was 97.4% (95% CI, 86.5-99.9). Median DoR was 8.3 months (interquartile range, 4.6-15.1). At a median follow-up of 23.54 months, the median PFS was 10.45 months (95% CI, 6.25-14.63) and median OS was 30.81 months (95% CI, 24.2-not reached). The most common grade 1 and/or 2 treatment-related adverse events (TRAE) were diarrhea, anorexia, dysgeusia, weight loss, and nausea. The most common grade 3 and/or 4 TRAEs were hypertension, hypophosphatemia, alanine transaminase elevation, diarrhea, and fatigue. There was one grade 5 TRAE of reversible posterior encephalopathy syndrome related to cabozantinib.

Conclusions

Pembrolizumab and cabozantinib treatment in patients with mRCC demonstrated encouraging preliminary efficacy and a manageable toxicity profile comparable with other available checkpoint inhibitor-tyrosine kinase inhibitor combinations.

Trial Registration

ClinicalTrials.gov Identifier: NCT03149822 https://clinicaltrials.gov/ct2/show/NCT03149822.

Significance

This study evaluated the safety and effectiveness of the combination of pembrolizumab and cabozantinib in patients with mRCC. The safety profile was manageable. The combination showed promising activity with an objective response rate of 65.8%, median PFS of 10.45 months, and median OS of 30.81 months.

Schwann Cell Insulin-like Growth Factor Receptor Type-1 Mediates Metastatic Bone Cancer Pain in Mice

Insulin growth factor-1 (IGF-1), an osteoclast-dependent osteolysis biomarker, contributes to metastatic bone cancer pain (MBCP), but the underlying mechanism is poorly understood. In mice, the femur metastasis caused by intramammary inoculation of breast cancer cells resulted in IGF-1 increase in femur and sciatic nerve, and IGF-1-dependent stimulus/non-stimulus-evoked pain-like behaviors. Adeno-associated virus-based shRNA selective silencing of IGF-1 receptor (IGF-1R) in Schwann cells, but not in dorsal root ganglion (DRG) neurons, attenuated pain-like behaviors. Intraplantar IGF-1 evoked acute nociception and mechanical/cold allodynia, which were reduced by selective IGF-1R silencing in DRG neurons and Schwann cells, respectively. Schwann cell IGF-1R signaling promoted an endothelial nitric oxide synthase-mediated transient receptor potential ankyrin 1 (TRPA1) activation and release of reactive oxygen species that, via macrophage-colony stimulating factor-dependent endoneurial macrophage expansion, sustained pain-like behaviors. Osteoclast derived IGF-1 initiates a Schwann cell-dependent neuroinflammatory response that sustains a proalgesic pathway that provides new options for MBCP treatment.

Prepartum measurement of serum biomarkers reflecting osteoclastic and osteoblastic bone metabolism for predicting the risk of milk fever in dairy cows

We investigated whether prepartum levels of serum bone biomarkers are related to the degree of parturient hypocalcaemia and risk of milk fever (MF) in dairy cows with advancing parity. A total of 58 late-pregnant cattle were assigned to four groups: nulliparous, primiparous, multiparous in the 2nd lactation and multiparous in the 3rd-5th lactation. The multiparous cows were further assigned to MF and non-MF groups according to the onset of MF. Serum samples were obtained from the cows during the 3 weeks prepartum to 5 d postpartum period for the measurement of serum calcium (Ca) and three bone biomarkers: tartrate-resistant acid phosphatase isoform 5b (TRAP5b), osteoprotegerin (OPG) and bone isoenzyme of alkaline phosphatase (ALP3). The ratios of OPG to TRAP5b (O/T ratio) and ALP3 to TRAP5b (A/T ratio) were calculated. The data from all cattle showed that the severity of hypocalcaemia at parturition increased with advancing parity/age. The MF cows had elevated serum TRAP5b activity and a decreased O/T ratio after parturition, suggesting an increased number of osteoclasts due to osteoclastogenesis, in response to severe hypocalcaemia. The MF cows showed lower serum ALP3 activity during the 3 weeks prepartum than the non-MF cows, therefore, prepartum osteoblast function was likely weak in the MF cows. During the 2-3 weeks prepartum, serum ALP3 activity and the A/T ratio had moderate associations with the serum Ca concentration at day 0 (day of calving) in the multiparous cows, and receiver operating characteristic curve analysis revealed that ALP3 activity had excellent ability to predict MF. In conclusion, prepartum serum ALP3 activity is a promising biomarker to predict MF in multiparous cows.

Immune checkpoint inhibitor-related hepatotoxicity: A review

The application of immune checkpoint inhibitors (ICI) in advanced cancer has been a major development in the last decade. The indications for ICIs are constantly expanding into new territory across different cancers, disease stages and lines of therapy. With this increased use, adverse events including immune checkpoint inhibitor-related hepatotoxicity (ICH) have emerged as an important clinical problem. This along with the introduction of ICI as first- and second-line treatments for advanced hepatocellular carcinoma makes ICH very relevant to gastroenterologists and hepatologists. The incidence of ICH varies between 1%-20% depending on the number, type and dose of ICI received. Investigation and management generally involve excluding differential diagnoses and following a stepwise escalation of withholding or ceasing ICI, corticosteroid treatment and adding other immunosuppressive agents depending on the severity of toxicity. The majority of patients with ICH recover and some may even safely recommence ICI therapy. Guideline recommendations are largely based on evidence derived from retrospective case series which highlights a priority for future research.

Biomechanical Properties of Metastatically Involved Osteolytic Bone

PURPOSE OF REVIEW

Skeletal metastasis involves the uncoupling of physiologic bone remodeling resulting in abnormal bone turnover and radical changes in bony architecture, density, and quality. Bone strength assessment and fracture risk prediction are critical in clinical treatment decision-making. This review focuses on bone tissue and structural mechanisms altered by osteolytic metastasis and the resulting changes to its material and mechanical behavior.

RECENT FINDINGS

Both organic and mineral phases of bone tissue are altered by osteolytic metastatic disease, with diminished bone quality evident at multiple length-scales. The mechanical performance of bone with osteolytic lesions is influenced by a combination of tissue-level and structural changes. This review considers the effects of osteolytic metastasis on bone biomechanics demonstrating its negative impact at tissue and structural levels. Future studies need to assess the cumulative impact of cancer treatments on metastatically involved bone quality, and its utility in directing multimodal treatment planning.

Anthropometric and blood data on a hand-reared captive Asian elephant (Elephas maximus) calf: A retrospective case report

The anthropometric and blood data of an unsuccessfully hand-reared Asian elephant (Elephas maximus) calf were retrospectively compared with the data for calves raised by their real mothers or allomothers, to identify potential reasons for poor outcomes in the hand-reared case. The hand-reared calf grew normally in terms of body weight and withers height. However, blood biochemical data suggested reduced bone metabolism, low immune status, and malnutrition during its life. Blood bone markers were measured to determine whether a skeletal disorder was present in the Asian elephant calf, which was not clear from the anthropometric data. Monitoring these parameters in hand-reared Asian elephant calves, with the aim of keeping them within the normal range, may increase the success rate of hand-rearing of Asian elephant calves.

Longitudinal evaluation of Wnt inhibitors and comparison with others serum osteoimmunological biomarkers in osteolytic bone metastasis

Bone and the immune system are closely linked: bone regulates the hematopoietic stem cells, which are precursors of immune cells, and several immunoregulatory cytokines influence the differentiation of bone cells, thus defining the osteoimmunological system. Cytokines and growth factors produced by immune and bone cells promote tumors in bone, supporting the vicious cycle of bone metastasis. Therefore osteoimmunological molecules linking the immune and bone systems could have diagnostic and prognostic potential for bone metastases. The osteoimmunologic Wnt pathway has been recently described as an important pathway with a vital role in bone carcinogenesis and metastatic progression. We examined the Wnt inhibitor DKK-1, sclerostin and several other osteoimmunological biomarkers involved in bone metastatic progression: RANKL, OPG, OPN, matrix metalloproteinase MMP-3 and the Receptor of Advanced Glycosylated End-products sRAGE. OPN and sclerostin proved good biomarkers of metastatic bone progression; the RANKL/OPG ratio was a good indicator of bone erosion in the metastatic process, while sRAGE had a protective role against metastatic progression in bone. These results serve to define a panel of new osteoimmunological biomarkers that could be useful in assessing the progress of osteolytic bone metastases.

Determination of serum bone-specific alkaline phosphatase isoenzyme activity in captive Asian elephants (Elephas maximus) using an agarose gel electrophoresis method

The bone-specific alkaline phosphatase (ALP) isoenzyme activity was measured in 51 serum samples from four captive Asian elephants (Elephas maximus) using a conventional method with wheat germ lectin precipitation and a commercial agarose gel electrophoresis (AGE) kit; the isoenzymes were designated as bone-specific ALP (BAP) and ALP isoenzyme 3 (ALP3), respectively. This study examined the suitability of the AGE kit for analyzing blood biochemistry in Asian elephants. The serum ALP3 and BAP activities were strongly positively correlated and met the evaluation criteria for agreement using Bland-Altman analysis. The results indicate that the AGE kit can be used to examine the blood biochemistry in Asian elephants instead of the conventional method.

Cyperenoic acid suppresses osteoclast differentiation and delays bone loss in a senile osteoporosis mouse model by inhibiting non-canonical NF-κB pathway

Cyperenoic acid is a terpenoid isolated from the root of a medicinal plant Croton crassifolius with a wide range of biological activities. In this study, the effects of cyperenoic acid on osteoclast differentiation were investigated both in vitro and in vivo using receptor activator of nuclear factor-κB ligand (RANKL)-induced bone marrow-derived osteoclasts and senescence-accelerated mouse prone 6 (SAMP6). Cyperenoic acid significantly suppressed RANKL-induced osteoclast differentiation at the concentrations with no apparent cytotoxicity. The half maximum inhibitory concentration (IC₅₀) for osteoclast differentiation was 36.69 μM ± 1.02. Cyperenoic acid treatment evidently reduced the expression of two key transcription factors in osteoclast differentiation, NFATc1 and c-Fos. Detailed signaling analysis revealed that cyperenoic acid did not affect MAPK pathways and canonical NF-κB pathway but impaired activation of p100/p52 in the non-canonical NF-κB pathway upon RANKL stimulation. Moreover, the expression of osteoclast-related genes, nfatc1, ctsk, irf8, acp5 and cfos were disrupted by cyperenoic acid treatment. The bone resorption activity by cyperenoic acid-treated osteoclasts were impaired. In a senile osteoporosis mouse model SAMP6, mice fed on diet supplemented with cyperenoic acid showed delay in bone loss, compared to the control. Taken together, plant-derived cyperenoic acid shows great potential as therapeutic agent for osteoporosis.

Serum activities of two bone markers in captive Asian elephants (Elephas maximus) at different ages

The blood biochemical analysis of bone markers could have a role in the early diagnosis of metabolic bone disease in animals; however, there is limited information on bone markers in captive Asian elephants (Elephas maximus). Serum samples from ten captive Asian elephants were obtained to clarify the relationship between age and the blood bone markers tartrate-resistant acid phosphatase isoform 5b (TRAP5b) and bone specific alkaline phosphatase (BALP). Serum TRAP5b and BALP activities were negatively correlated with age. A positive correlation was observed between TRAP5b activity and BALP activity. These results may contribute to the health management of captive Asian elephants.

Clinical outcome and prognostic factors in hepatocellular carcinoma patients with bone metastases medicated with zoledronic acid

AIMS

We retrospectively analyzed the clinical outcome and prognostic parameters in patients with hepatocellular carcinoma (HCC) and bone metastases who had received treatment with zoledronic acid (ZOL).

METHODS

Ninety-nine HCC patients with bone metastases who had been treated with ZOL were enrolled in this retrospective cohort study. We analyzed the prognostic factors, including serum N-telopeptide of type I collagen (NTX) levels, as bone metabolism markers.

RESULTS

The median overall survival (OS) time was 11.5 months. Child-Pugh grade A (P = 0.004) and intrahepatic tumor stage (IHTS) T0-3 (P = 0.010) correlated significantly with favorable OS. In 46 patients with grade A and T0-3, receiver operating characteristic curve analysis defined 16 nmol BCE/L serum NTX as the cut-off level for median OS. Multivariate analysis identified baseline serum NTX <16 nmol BCE/L (P = 0.045) as the only significant and independent determinant of OS.

CONCLUSION

Low baseline serum NTX level correlated with favorable outcome in bone metastatic HCC patients with Child-Pugh grade A and IHTS T0-3 treated with ZOL.

Bone targeted therapy for preventing skeletal-related events in metastatic breast cancer

Cancer cells can alter physiological mechanisms within bone resulting in high bone turnover, and consequently in skeletal-related events (SREs), causing severe morbidity in affected patients. The goals of bone targeted therapy, as bisphosphonates and denosumab, are the reduction of incidence and the delay in occurrence of the SREs, to improve quality of life and pain control. The toxicity profile is similar between bisphosphonates and denosumab, even if pyrexia, bone pain, arthralgia, renal failure and hypercalcemia are more common with bisphosphonates, while hypocalcemia and toothache are more frequently reported with denosumab. Osteonecrosis of the jaw (ONJ) occurred infrequently without statistically significant difference. The present review aims to provide an assessment on bone targeted therapies for preventing the occurrence of SREs in bone metastatic breast cancer patients, critically analyzing the evidence available so far on their effectiveness, in light of the different mechanisms of action. Thus, we try to provide tools for the most fitting treatment of bone metastatic breast cancer patients. We also provide an overview on the usefulness of bone turnover markers in clinical practice and new molecules currently under study for the treatment of bone metastatic disease.

Effect of neoadjuvant chemotherapy on the serum levels of bone turnover markers in women with early-stage breast cancer

Background

To evaluate effects of neoadjuvant chemotherapy on the bone turnover markers of preoperational breast cancer patients.

Methods

Forty-one breast cancer patients (29 premenopausal and 12 postmenopausal) and 60 healthy women (30 premenopausal and 30 postmenopausal) aged 30-64 years, were evaluated for their bone status. Serum levels of the bone formation markers PINP and BAP, as well as the resorption markers ICTP and β-Crosslaps in addition to E2, FSH, 25(OH)D and PTH were measured at the initial diagnosis and at 24 hours after each four chemotherapy cycles. BMD T-scores were determined in 12 patients 6 months after the neoadjuvant chemotherapies.

Results

The baseline levels of both bone formation and resorption markers in premenopausal patients were higher than in premenopausal healthy women (p<0.05), while no statistic difference was observed between postmenopausal patients and postmenopausal healthy women. Regardless of the menopausal status, chemotherapy increased the ICTP and β-Crosslaps levels (p<0.05), but decreased the BAP and PINP levels (p<0.05), the later one significantly more with Taxane medication (p<0.01, p<0.05). Chemotherapy caused significant decreases of 25(OH)D levels in premenopausal (p<0.01) and postmenopausal (p<0.05) patients, however, did not affect the PTH concentrations. In premenopausal patients the E2 level decreased, while the FSH level increased after chemotherapy (p<0.05). Patients with pronounced ICTP and β-Crosslaps combined with reduced BAP and PINP serum concentrations after neoadjuvant chemotherapies were prone to develop osteoporosis 6 month later.

Conclusions

Neoadjuvant chemotherapy appeared to promote bone resorption and inhibit bone formation in both postmenopausal and premenopausal early-stage breast patients.

Relationship between oxidative stress and bone mass in obesity and effects of berry supplementation on bone remodeling in obese male mice: an exploratory study

Berry consumption can prevent bone loss. However, the effects of different berries with distinct anthocyanin composition have not been thoroughly examined. The present study compared the effects of blueberry, blackberry, and black currant on bone health using a mouse model of diet-induced obesity. To investigate the effect of different berry supplements against a high-fat (HF) diet in vivo, 40 HF diet-induced obese (DIO) C57BL mice were assigned into four groups and fed a HF diet (35% w/w) with or without berry supplementation for 12 weeks (n=10). We measured adipose tissue mass (epididymal and retroperitoneal), plasma antioxidant, bone-related biomarkers, femur bone mineral density (BMD), and bone mineral content (proximal and distal). Adipose masses were negatively correlated with proximal BMD, but positively associated with plasma superoxide dismutase (SOD) concentrations (P<.001). Berry supplementation did not change the plasma ferric reducing antioxidant power, SOD, and insulin-like growth factor-1. However, the black currant group exhibited greater plasma alkaline phosphatase compared with the control group (P<.05). BMD in the distal epiphysis was significantly different between the blueberry and blackberry group (P<.05). However, berry supplementation did not affect bone mass compared with control. The present study demonstrates a negative relationship between fat mass and bone mass. In addition, our findings suggest that the anthocyanin composition of berries will affect bone turnover, warranting further research to investigate the underlying mechanisms.

Nuclear factor-kappa B ligand and osteoprotegerin levels in serum and gingival crevicular fluid in patients with bone metastases treated with zoledronic acid

Bone metastases are frequently observed in patients with certain types of cancer and are significant cause of morbidity. Zoledronic acid (ZA) is routinely prescribed for patients with bone metastases by affecting osteoclast function. We aimed to assess the effect of ZA over time in patients with bone metastases by analyzing novel bone turnover marker levels including receptor activator of nuclear factor-k B ligand (RANKL) and osteoprotegerin (OPG) in serum and gingival crevicular fluid (GCF). Also, associations between these bone turnover markers with hematological and biochemistry dysregulation were studied. The study enrolled patients with bone metastases including 32 patients diagnosed with solid tumors and 15 patients with multiple myeloma. In these patients, GCF and serum RANKL and OPG levels were measured and compared with measures of hematological and biochemical parameters before and after 3 months of ZA therapy. Mean subject age was 54 years old with a range of 28-80 years. Skeletal-related events were observed in 8.5% of all patients. After the 3-month treatment of ZA therapy, no significant differences were found in serum and GCF levels of RANKL and OPG when compared with before treatment levels. GCF RANKL levels at baseline and following 3 months of ZA therapy were significantly higher in patients with solid tumors when compared patients diagnosed with multiple myeloma (p=0.001; p<0.001, respectively). GCF OPG levels after the entire course of ZA therapy were greater in patients with 5 or more bone metastases (p=0.04). For patients with multiple myeloma, control GCF OPG was negatively correlated with control platelet and WBC counts (p=0.018 and p=0.027, respectively). A negative correlation was observed between control serum RANKL and control serum OPG levels in myeloma patients (p=0.001). After 3 months of ZA therapy, no significant differences were observed in GCF and serum RANKL and OPG levels when compared with baseline. A negative correlation was observed between serum control RANKL and OPG levels in myeloma patients. OPG levels were greater in patients with 5 or more bone metastases. In patients diagnosed with multiple myeloma, GCF OPG levels were negatively associated with WBC and platelet counts.

Hepcidin deficiency undermines bone load-bearing capacity through inducing iron overload

Osteoporosis is one of the leading disorders among aged people. Bone loss results from a number of physiological alterations, such as estrogen decline and aging. Meanwhile, iron overload has been recognized as a risk factor for bone loss. Systemic iron homeostasis is fundamentally governed by the hepcidin-ferroportin regulatory axis, where hepcidin is the key regulator. Hepcidin deficiency could induce a few disorders, of which iron overload is the most representative phenotype. However, there was little investigation of the effects of hepcidin deficiency on bone metabolism. To this end, hepcidin-deficient (Hamp1(-/-)) mice were employed to address this issue. Our results revealed that significant iron overload was induced in Hamp1(-/-) mice. Importantly, significant decreases of maximal loading and maximal bending stress were found in Hamp1(-/-) mice relative to wildtype (WT) mice. Moreover, the levels of the C-telopeptide of type I collagen (CTX-1) increased in Hamp1(-/-) mice. Therefore, hepcidin deficiency resulted in a marked reduction of bone load-bearing capacity likely through enhancing bone resorption, suggesting a direct correlation between hepcidin deficiency and bone loss. Targeting hepcidin or the pathway it modulates may thus represent a therapeutic for osteopenia or osteoporosis.

[Correlation of the levels of the bone turnover markers BAP and β-CTX with bone metastasis progress in lung cancer patients]

背景与目的

肺癌易发生骨转移，Ⅰ型胶原羧基端肽β特殊序列（β isomer of C-terminal telopeptide of type Ⅰ collagen, β-CTX）和骨源性碱性磷酸酶（bone-specific alkaline phosphates, BAP）在骨质代谢中是重要的生化标记物，本研究旨在探讨骨代谢生化指标和肺癌骨转移进展程度的相关性，有助于早期判断是否有肺癌骨转移的发生。

方法

天津市人民医院2009年7月-2012年7月共收治92例肺癌并发生骨转移患者，全部病例其原发灶均经细胞学检查证实，骨转移灶的数目及类型经ECT结合X线片、CT证实，采用ELISA方法检测血β-CTX、BAP的浓度水平。

结果

收集的92例肺癌伴骨转移的患者中，转移灶 < 3处为58例，≥3处为34例；溶骨型68例，成骨型9例，混合型15例。血β-CTX、BAP水平在不同的骨转移数目组间差异有统计学意义（P < 0.05），β-CTX在肺癌溶骨型骨转移患者中具有较高的敏感性。

结论

骨代谢生化指标β-CTX、BAP对肺癌骨转移具有辅助诊断意义，是判断转移进展程度的良好指标。

Bisphosphonates and bone metastases: current status and future directions

Since bone metastases in advanced cancer are common and frequently lead to skeletal-related morbid complications, their treatment remains a major challenge in cancer therapy. Bisphosphonates not only significantly decreased the odds ratios for fracture, need for radiotherapy, and incidence of hypercalcemia, but also had proven ability in the preservation of the 3D microstructure of bone that is responsible for bone stability. Bisphosphonates are well tolerated and have a very low incidence of serious side effects. Consequently, bisphosphonates have become the standard of care for the treatment of malignant bone disease. Benefits of bisphosphonate treatment appears to be more pronounced with longer treatment, indicating that they should be continued until no longer clinically relevant. As this advice has substantial implications on resources, it is essential that the use of bisphosphonates is evidence based.

The osteoblastic and osteoclastic interactions in spinal metastases secondary to prostate cancer

Prostate cancer (PC) is one of the most common cancers arising in men and has a high propensity for bone metastasis, particularly to the spine. At this stage, it often causes severe morbidity due to pathological fracture and/or metastatic epidural spinal cord compression which, if untreated, inevitably leads to intractable pain, neurological deficit, and paralysis. Unfortunately, the underlying molecular mechanisms driving growth of secondary PC in the bony vertebral column remain largely unknown. Further investigation is warranted in order to identify therapeutic targets in the future. This review summarizes the current understanding of PC bone metastasis in the spine, highlighting interactions between key tumor and bone-derived factors which influence tumor progression, especially the functional roles of osteoblasts and osteoclasts in the bone microenvironment through their interactions with metastatic PC cells and the critical pathway RANK/RANKL/OPG in bone destruction.

Clinical significance of serum BAP, TRACP 5b and ICTP as bone metabolic markers for bone metastasis screening in lung cancer patients

BACKGROUND

We investigated the clinical significance of serum bone-specific alkaline phosphatase (BAP), tartrate-resistant acid phosphatase isoform 5b (TRACP 5b) and type I collagen carboxyterminal telopeptide (ICTP) as bone metabolic markers for bone metastasis (BM) screening in lung cancer patients.

METHODS

Newly diagnosed advanced lung cancer patients with (N = 130) and without (N = 135) BM were enrolled in the study. Serum BAP, TRACP 5b and ICTP were measured before the treatment.

RESULTS

BAP, TRACP 5b and ICTP values were higher in patients with BM compared with patients without BM (all P < 0.0001). Area under ROC curve (AUC) of BAP, TRACP 5b and ICTP was 0.760, 0.753 and 0.835 (all P < 0.0001), respectively. The cut-off values for BAP, TRACP 5b and ICTP were 21.8 μg/l, 7.8 U/l and 8.8 μg/l, respectively. When TRACP 5b and ICTP were combined, AUC was elevated to 0.895 (P < 0.0001), and the cut-off values were TRACP 5b 7.6 U/l and ICTP 8.4 μg/l.

CONCLUSIONS

We conclude that serum BAP, TRACP 5b and ICTP may serve as useful tools for BM screening in lung cancer patients.

Postoperative simple biochemical markers for prediction of bone metastases in Egyptian breast cancer patients

Objective:

The present study was undertaken to identify patient populations at high risk for bone metastases (BM) at any time after diagnosis of operable breast cancer.

Subjects and methods:

A total number of 59 cases with breast cancer after mastectomy was subdivided into two main groups that included 30 patients with radiologically confirmed BM and 29 patients with no bone metastasis (NBM). Patients with NBM were formerly observed for a one-year follow-up interval to monitor the development of bone metastasis (new BM). Parameters included a full blood picture, tumour markers (carcinoembryonic antigen and CA 15.3) and some biochemical markers (vascular endothelial growth factor and zinc levels, as well as tartrate-resistant acid phosphatase and alkaline phosphatase activities).

Results:

A significant elevation was recorded in carcinoembryonic antigen level and alkaline phosphatase activity, as well as inflammation and vascularisation markers at the time of primary diagnosis in patients with BM, compared with those without BM. CA 15.3 was significantly higher in the new BM group as compared with the other two groups (patients free of bone metastasis [free BM] and BM). According to the likelihood ratio, a panel of single, calculated as well as combined markers was proposed to predict BM within one year in breast cancer patients.

Conclusion:

Vascularisation and inflammation markers, as well as CA 15.3 are predictive of bone recurrence within one year in breast carcinoma patients. We suggest that in cancer validation studies it is imperative to search for markers that link to the premetastatic process and to determine what type of mechanism is active in each stage.

Management of skeletal-related events in patients with advanced prostate cancer and bone metastases: Incorporating new agents into clinical practice

Skeletal-related events (SREs) are a common complication of bone metastases, and have serious negative consequences for patients with castrate-resistant prostate cancer (CRPC). SREs can lead to severe pain, increased risk of death, increased health care costs and reduced quality of life. Until recently, zoledronic acid has been the sole standard of care for the prevention of SREs in men with CRPC with bone metastases. Denosumab, a receptor activator of nuclear factor kappa-B ligand (RANK-L) inhibitor, has been recently approved for use in Canada for this indication, thus presenting another option for these patients. Denosumab was shown to be superior to zoledronic acid in delaying the time to first or subsequent SREs in CRPC patients with bone metastases. This review discusses current and previous trials examining agents designed to prevent SREs in men with CRPC and bone metastases. It also discusses the practical aspects of administering a bone-targeted therapy, including choosing a bone-targeted therapy, monitoring at the onset and during therapy, switching from one therapy to another, and assessing potential complications.

The role of the bone microenvironment in skeletal metastasis

The bone microenvironment provides a fertile soil for cancer cells. It is therefore not surprising that the skeleton is a frequent site of cancer metastasis. It is believed that reciprocal interactions between tumour and bone cells, known as the “vicious cycle of bone metastasis” support the establishment and orchestrate the expansion of malignant cancers in bone. While the full range of molecular mechanisms of cancer metastasis to bone remain to be elucidated, recent research has deepened our understanding of the cell-mediated processes that may be involved in cancer cell survival and growth in bone. This review aims to address the importance of the bone microenvironment in skeletal cancer metastasis and discusses potential therapeutic implications of novel insights.

Excess iron undermined bone load-bearing capacity through tumor necrosis factor-α-dependent osteoclastic activation in mice

Iron overload has been associated with bone mass loss. To elucidate the effects of excess iron on bone metabolism, an iron-overloading mouse model was established by administering iron-dextran at 250 mg/kg to female BALB/c mice. After 4 weeks, the mice were sacrificed and the biomechanical properties of the femurs were examined. The results suggested a notable decrease of the maximal bending stress and the modulus of bending elasticity in the femurs obtained from the excess iron-treated mice compared to the control mice. The levels of the serum osteocalcin, C-telopeptide of type I collagen (CTX-1) and tumor necrosis factor-α (TNF-α) were measured in order to investigate the underlying mechanism responsible for the excess iron-induced bone strength reduction. Overall, the results suggested that iron overload resulted in a marked reduction of bone load-bearing capacity through a TNF-triggered osteoclast differentiation and resorption mechanism.

Clinical usefulness of bone markers in prostate cancer with bone metastasis

Bone metastases occur in approximately 70% of patients with advanced prostate cancer. Skeletal-related events have been correlated with reduced survival and quality of life of patients with prostate cancer. Biochemical markers of bone metabolism (e.g. bone formation, bone resorption, osteoclastogenesis) might meet an unmet need for useful, non-invasive and sensitive surrogate information for following patients' skeletal health. Recently, zoledronic acid and denosumab have been proven to have the potential for preventing skeletal-related events among prostate cancer patients with bone metastasis. An improved understanding of the mechanisms underlying bone metastasis has also led to the recognition of multiple molecular targets and advances in therapy. However, estimating the efficacy of these agents is difficult. A clinical trial for castration-resistant prostate cancer is currently underway based on the definition of The Prostate Cancer Clinical Trials Working Group, and bone turnover markers are being used as conventional end-points for the clinical trial. Bone turnover markers are useful surrogate markers reflecting the effect of new therapeutic drugs and prognosis, as well as assessment of bone metastases. In particular, N-terminal cross-linked telopeptide of type 1 collagen and bone-specific alkaline phosphatase are widely used bone metabolism markers, and offer reliable surrogate markers to detect bone metastatic spread and to predict prognosis for prostate cancer patients with bone metastases.

A molecular description of acid phosphatase

Acid phosphatase is ubiquitous in distribution in various organisms. Although it catalyzes simple hydrolytic reactions, it is considered as an interesting enzyme in biological systems due to its involvement in different physiological activities. However, earlier reviews on acid phosphatase reveal some fragmentary information and do not give a holistic view on this enzyme. So, the present review summarizes studies on biochemical properties, structure, catalytic mechanism, and applications of acid phosphatase. Recent advancement of acid phosphatase in agricultural and clinical fields is emphasized where it is presented as potent agent for sustainable agricultural practices and diagnostic marker in bone metabolic disorders. Also, its significance in prostate cancer therapies as a therapeutic target has been discussed. At the end, current studies and prospects of immobilized acid phosphatase are included.

Prevention of chemotherapy-induced osteoporosis by cyclophosphamide with a long-acting form of parathyroid hormone

BACKGROUND

Most chemotherapeutics reduce bone mineral density (BMD) and increase risk for fractures by causing gonadal suppression, which in turn increases bone removal. Cyclophosphamide (CYP) also has a direct effect of inhibiting bone formation and removal, making the resulting bone loss particularly difficult to treat with antiresorptive therapy.

AIM

We tested whether a single dose of the anabolic agent PTH linked to a collagen binding domain (PTHCBD) could prevent the effects of CYP-induced bone loss.

METHODS

Mice received either buffer alone, CYP, or CYP+ PTH-CBD. BMD and alkaline phosphatase were measured every 2 weeks for a total of 8 weeks.

RESULTS

After 6 weeks, mice treated with CYP showed expected reductions in BMD (increase from baseline: 7.4 ± 6.9 vs 24.35 ± 4.86% in mice without chemotherapy, p<0.05) and decrease in alkaline phosphatase levels (42.78 ± 6.06 vs 60.62 ± 6.23 IU/l in mice without chemotherapy, p<0.05), consistent with osteoporosis from impaired bone formation. Administration of a single dose of PTH-CBD (320 μg/kg ip) prior to CYP treatment improved BMD (change from baseline: 23.4 ± 5.4 vs 7.4 ± 6.9%, CYP treatment alone, p<0.05) and increased alkaline phosphatase levels (50.14 ± 4.86 vs 42.78 ± 6.06 IU/l in CYP treatment alone, p<0.05). BMD values and alkaline phosphatase levels were restored to those seen in mice not receiving chemotherapy.

CONCLUSIONS

A single dose of PTHCBD prior to chemotherapy reversed CYP-induced suppression of bone formation and prevented CYP-induced bone loss in mice.

Skeletal metastasis in renal cell carcinoma: current and future management options

Metastasis to the skeleton is common in advanced renal cancer and leads to debilitating skeletal complications including severe pain, increased fracture rate and spinal cord compression. The incidence of renal cell carcinoma is increasing by around 2% per year and recent advances in targeted anti-angiogenic therapy for advanced disease are expected to lead to longer survival times. The clinical management of metastatic bone disease in renal cell carcinoma therefore merits greater focus than hitherto. Bone metastases arising from renal cancer are highly osteolytic and particularly destructive. Fortunately, the continuing development of anti-resorptive drugs is revolutionising the medical management of metastatic bone disease across many tumour types and making a major impact on quality of life. The bisphosphonate zoledronic acid is now licensed for use in advanced renal cell carcinoma and appears to yield a greater benefit in terms of reduction in skeletal related events than in bone metastases arising from other tumour types. Drugs which are directed at specific targets in the bone metastasis pathway are in development, including denosumab, a fully human monoclonal antibody against receptor activator of nuclear factor kappa B ligand, which has recently been licensed in the United States for use in renal cell carcinoma, with European licensing expected soon. This review examines the increasing options for treatment of metastatic bone disease in renal cell carcinoma, with a focus on drug-based advances and progress in the development of existing and new biomarkers to support clinical management.

Bone-marker levels in patients with prostate cancer: potential correlations with outcomes

PURPOSE OF REVIEW

The skeleton is typically the first site of metastasis in patients with prostate cancer, and bone metastases can result in severe bone pain and potentially debilitating fractures. Although bone scans are a reliable means of assessing osteoblastic lesions, tools for monitoring early changes in bone health are lacking. Biochemical markers of bone turnover might fulfill this unmet need.

RECENT FINDINGS

Correlative studies have suggested that bone-marker levels may have utility in assessing disease progression and response to bone-directed therapy. Elevated levels of the markers, N-telopeptide of type I collagen and bone-specific alkaline phosphatase, are associated with higher rates of death and skeletal-related events in the bone metastasis setting. Marker levels also correlate with response to zoledronic acid treatment, and similar data with the investigational agent, denosumab, are emerging.

SUMMARY

Changes in bone-marker levels reflect alterations in skeletal homeostasis and can provide important insights into bone disease progression and response to bone-directed therapy in patients with prostate cancer. More mature data from currently ongoing clinical trials will provide further insight on the utility of marker assessments as an adjunct to established monitoring methods in prostate cancer.

Adenylate cyclase and calmodulin-dependent kinase have opposite effects on osteoclastogenesis by regulating the PKA-NFATc1 pathway

Nuclear factor of activated T cells c1 (NFATc1) is a transcription factor crucial for the differentiation of osteoclasts. In this study we discovered new signaling pathways involving cAMP regulators that modulate NFATc1 during osteoclastogenesis. The osteoclast differentiation factor receptor activator of NF-κB ligand (RANKL) increased the expression of adenylate cyclase 3 (AC3), accompanied by a rise in the intracellular cAMP level in osteoclasts. The knockdown of AC3 enhanced in vitro osteoclastogenesis and in vivo bone resorption, whereas cAMP-elevating agents showed opposite effects. The antiosteoclastogenic effect of the AC3-cAMP pathway was mediated by the inhibition of NFATc1 nuclear translocation and its autoamplification via a protein kinase A (PKA)-dependent mechanism. RANKL has been shown to activate Ca(2+) /calmodulin-dependent protein kinases (CaMKs). Knockdown or catalytic inhibition of CaMKs elevated intracellular cAMP levels in RANKL-treated osteoclast precursors and suppressed the activation of NFATc1. Taken together, our results demonstrate a pivotal role for the cAMP-PKA-NFATc1 signaling pathway during osteoclast differentiation, suggesting a mechanism by which osteoclastogenesis is fine-tuned by a balance between AC3 and CaMKs activities.

Consensus on the utility of bone markers in the malignant bone disease setting

Biochemical markers of bone turnover provide insight into ongoing rates of skeletal metabolism and tumor-bone interactions in patients with malignant bone disease. This article reviews the available recent evidence assessing the potential of bone markers for detecting and monitoring malignant bone lesions in patients with advanced cancers, and for assessing overall skeletal health and response to antiresorptive therapies in patients at all stages of cancer progression. Most data thus far are for urinary N-terminal cross-linked telopeptide of type I collagen (NTX) in predicting risks of skeletal morbidity and death and monitoring response to zoledronic acid in patients with bone metastases. Ongoing studies are evaluating such correlations for other markers and therapies. Emerging evidence suggests that bone markers may help identify patients at high risk for bone metastasis or bone lesion progression, thereby allowing improved follow-up. Results from ongoing clinical trials evaluating such potential applications of bone markers are awaited.

Evolving role of bone biomarkers in castration-resistant prostate cancer

The preferential metastasis of prostate cancer cells to bone disrupts the process of bone remodeling and results in lesions that cause significant pain and patient morbidity. Although prostate-specific antigen (PSA) is an established biomarker in prostate cancer, it provides only limited information relating to bone metastases and the treatment of metastatic bone disease with bisphosphonates or novel noncytotoxic targeted or biological agents that may provide clinical benefits without affecting PSA levels. As bone metastases develop, factors derived from bone metabolism are released into blood and urine, including N- and C-terminal peptide fragments of type 1 collagen and bone-specific alkaline phosphatase, which represent potentially useful biomarkers for monitoring metastatic bone disease. A number of clinical trials have investigated these bone biomarkers with respect to their diagnostic, prognostic, and predictive values. Results suggest that higher levels of bone biomarkers are associated with an increased risk of skeletal-related events and/or death. As a result of these findings, bone biomarkers are now being increasingly used as study end points, particularly in studies investigating novel agents with putative bone effects. Data from prospective clinical trials are needed to validate the use of bone biomarkers and to confirm that marker levels provide additional information beyond traditional methods of response evaluation for patients with metastatic prostate cancer.

Biochemical markers of bone turnover and clinical outcomes in men with prostate cancer

OBJECTIVES

Disrupted skeletal homeostasis is common in patients with prostate cancer. Low bone density is common at diagnosis, and fracture risk is further elevated by the effects of androgen-deprivation therapy. Later in the disease course, bone metastases can result in skeletal morbidity. Although prostate-specific antigen (PSA) levels can provide important insights into overall disease progression, convenient, noninvasive tools for monitoring skeletal health are lacking. Biochemical markers released into serum and urine as a result of bone turnover might fulfill this unmet need. The objectives of this article are to assess current evidence examining the potential utility of bone turnover markers for monitoring skeletal health, bone disease progression, and response to antiresorptive therapies in the prostate cancer setting.

METHODS

Published articles and abstracts from major oncology or urology congresses pertaining to the use of bone turnover markers to monitor skeletal health and disease progression were identified and assessed for relevance and methodologic stringency.

RESULTS

Several randomized trials and correlative studies support the utility of bone marker level changes to assess disease progression in the metastatic setting, bone health during hormonal therapy, and response to bisphosphonate therapy. The available data support potential associations between levels of the collagen type I telopeptides (NTX and CTX) and the severity of metastatic bone disease as well as outcomes during antiresorptive therapy. Evidence linking bone marker level changes with early diagnosis of skeletal metastases is emerging. Although several markers have shown promising results in correlative studies, results from ongoing prospective trials are needed to establish the role of bone markers in this setting.

CONCLUSIONS

Bone marker levels reflect ongoing skeletal metabolism and can provide important insights into bone health and response to bisphosphonate therapy in patients with prostate cancer. The data supporting a role for bone markers to monitor skeletal disease progression and response to zoledronic acid therapy are especially strong. Bone marker assessments may complement established diagnostic and monitoring paradigms in prostate cancer.

Markers of bone remodeling and skeletal morbidity in patients with solid tumors metastatic to the skeleton receiving the biphosphonate zoledronic acid

The molecular triad, which includes the receptor activator of nuclear factor kappa-B ligand (RANKL), its receptor RANK, and the endogenous soluble RANKL decoy receptor osteoprotegerin (OPG), has emerged as an important determinant of bone metabolism. We aimed to evaluate the effect of treatment with the biphosphonate zoledronic acid (ZA) on biochemical markers of bone remodeling and to detect possible correlations of markerlevel changes with skeletal morbidity and clinical outcomes in patients with solid tumors and osseous metastases. The following serum markers were measured at the onset of skeletal metastases and after 6 months of treatment with ZA (4 mg intravenously monthly) in 70 patients with breast (n = 30), lung (n = 18), or prostate (n = 22) cancer: RANKL, OPG, C-terminal cross-linking telopeptide of type I collagen (CTX), tartrate-resistant acid phosphatase isoform 5b (TRACP-5b), bone-specific alkaline phosphatase (bALP), and osteopontin (OPN). Logistic regression models were applied to assess the correlation between marker-level changes and skeletal related events (SRE, primary endpoint), recurrence or progression, and death. Within a median follow-up of 32 months, 34 patients (48.6%) presented with at least 1 SRE and 48 patients (68.6%) relapsed. The RANKL/OPG ratio was upregulated in patients with breast and lung cancer, and it tended to decline after treatment with ZA, whereas prostate cancer patients presented with profound elevation of OPG only that persisted after treatment. CTX levels were significantly reduced after treatment in the whole study population (P = 0.003). None of the markers was able to predict skeletal morbidity or clinical outcomes independently of well-established prognostic clinical parameters.

Fluorometric method for measuring plasma tartrate-resistant acid phosphatase isoform 5b and its application in cattle

This study determined the appropriate biochemical assay for measuring plasma tartrate-resistant acid phosphatase isoform 5b (TRAP5b) activity; this information is important to clarify the relationship between plasma TRAP5b and known biochemical bone markers in cattle. When plasma TRAP5b was measured using fluorometric and spectrophotometric methods, hemolysis products in plasma did not affect the former method. In plasma from healthy cattle, there was a good correlation (r=0.66) between the 2 methods. In age-related profiles, plasma TRAP5b (r=-0.53), hydroxyproline (HYP, r=-0.56) and bone-specific alkaline phosphatase (BALP, r=-0.44) showed significant negative correlations with age; these three parameters decreased until 4 or 5 years of age and then remained constant. There were significant correlations between TRAP5b and HYP (r=0.83) or BALP (r=0.83). Our results show that the fluorometric assay can be performed with a high degree of precision and reproducibility without interference from hemolysis, and that the age-related changes in plasma TRAP5b, HYP, and BALP constitute additional background values for clinical guidance in bovine medicine.

Multiple myeloma: changes in serum C-terminal telopeptide of collagen type I and bone-specific alkaline phosphatase can be used in daily practice to detect imminent osteolysis

Objective: Monitoring of bone disease in multiple myeloma is becoming increasingly important because bone-protecting treatment with bisphosphonate is becoming restricted after the awareness of osteonecrosis of the jaw. Despite the potential of biochemical markers of bone remodeling to monitor dynamic bone turnover, they are not used in everyday practice. Here, we investigate their usefulness to detect imminent progressive osteolysis in relapsing patients with multiple myeloma. Methods: In an unselected cohort of 93 patients, we measured the bone resorption markers C-terminal telopeptide of collagen type I (CTX-I), C-terminal cross-linked telopeptide of type-I collagen generated by MMPs (ICTP), N-terminal cross-linked telopeptide of type-I collagen (NTX-I), and the bone formation marker bone-specific alkaline phosphatase (bALP) monthly for 2 yr. Retrospectively, we identified 40 cases where patients had progressive disease. We investigated how the bone markers developed prior to disease progression. Results: We observed that CTX-I and bALP changed significantly before progressive disease were recognized. More interestingly, these changes differed depending on whether concurrent progressive osteolysis was present. In patients with progressive osteolysis, there was a large increase in bone resorption which was not compensated by increased bone formation. In contrasts, patients with stable bone disease had only a slight increase in bone resorption which was compensated by concurrent increased bone formation. By calculating a patient-specific CTX-I/bALP ratio, we quantified the risk a patient experiences if the ratio increases. Conclusion: By analyzing patient-specific changes in the ratio of CTX-I/bALP, we might tailor treatment with bone-protecting agents in the individual patient.

Biology and clinical significance of tartrate-resistant acid phosphatases: new perspectives on an old enzyme

Type 5 tartrate-resistant acid phosphatase (TRAP) has been a clinically relevant biomarker for about 50 years. It has always been a reliable and specific cytochemical marker for hairy cell leukemia and for differentiated cells of monocytic lineage. Only recently has the test for serum TRAP activity been accepted as sensitive and specific enough for clinical use as a marker of osteoclasts and bone resorption. This has come about through steady advances in knowledge about TRAP enzymology, structure, function, and molecular regulation and a consequent appreciation that TRAP isoforms 5a and 5b have very different clinical significance. As a measure of osteoclast number and bone resorption, TRAP 5b has diagnostic and prognostic applications in osteoporosis, cancers with bone metastasis, chronic renal failure, and perhaps other metabolic and pathologic bone diseases. Serum TRAP 5a, on the other hand, has no relationship to bone metabolism but seems instead to be a measure of activated macrophages and chronic inflammation. Exploration of the real clinical usefulness of serum TRAP 5a for diagnosis and disease management in a wide variety of chronic inflammatory diseases is only now beginning. This perspective traces the important basic scientific developments that have led up to the refinement of serum TRAP isoform immunoassays and their validation as biomarkers of disease. Many unanswered questions remain, providing a wealth of opportunity for continued research of this multifaceted enzyme.

Abnormal bone remodeling process is due to an imbalance in the receptor activator of nuclear factor-kappaB ligand (RANKL)/osteoprotegerin (OPG) axis in patients with solid tumors metastatic to the skeleton

The role of receptor activator of nuclear factor-kappaB ligand (RANKL)/osteoprotegerin (OPG) system, and osteopontin (OPN) was studied in patients with solid tumors metastatic to the bone in relation to the type of malignancy and the neoplastic burden to the skeleton. Levels of soluble RANKL (sRANKL), OPG and OPN were assessed in 61 patients with breast, lung and prostate cancer with newly-diagnosed metastasis to the bone, in parallel with bone resorption [C-telopeptide of type-I collagen (CTX), tartrate-resistant acid phosphatase-5b (TRACP-5b)] and bone formation markers [bone-alkaline phosphatase (bALP), osteocalcin (OC), and C-terminal propeptide of collagen type-I (CICP)]. Patients had elevated serum levels of sRANKL, OPG, OPN, TRACP-5b, and bALP, and reduced OC levels compared to controls. OPG correlated with the extent of metastatic bone burden. Patients with breast and lung cancer shared increased levels of sRANKL, OPG, and OPN whereas prostate cancer patients had elevated values of OPG and bALP only. These results suggest that patients with solid tumors metastatic to the bone have severe disruption of the sRANKL/OPG axis. Breast and lung cancer seem to exert their osteolytic action through upregulation of the sRANKL/OPG system and OPN, whereas prostate cancer seems to provoke profound elevation of OPG levels only, thus leading to increased osteoblastic activity.

Treatment Options for Breast Cancer and Bone Metastases

The most common destination for breast cancer metastases is bone. If bone metastases are detected, treatment algorithms should include the continuation of cytoreductive therapy with the addition of treatment to counter skeletal-related events, including bone pain. The range of current treatment options includes bisphosphonates, surgical intervention to improve structural integrity and palliative focal radiotherapy. This article focuses on the role of bisphosphonate therapy in metastatic breast cancer. Bisphosphonate therapy significantly reduces the impact of skeletal-related events, reduces bone pain and increases patient quality of life. Our current understanding is that bisphosphonates may also disrupt the metastatic process and reduce the development of bone lesions. Ultimately, this may lead to further expansion of bisphosphonate-based therapy in the future.

Bone markers and their prognostic value in metastatic bone disease: clinical evidence and future directions

BACKGROUND

Bone metastases are prevalent among patients with advanced solid tumors. Metastatic bone disease alters bone homeostasis, resulting in reduced bone integrity and, consequently, increased skeletal complications. Biochemical markers of bone metabolism may meet an unmet need for useful, noninvasive, and sensitive surrogate information for following patients' skeletal health.

MATERIALS AND METHODS

Data for this review were identified by searches of PubMed, and references from relevant articles using the search terms "bone markers" or individual bone marker nomenclature, "cancer," and "metastases." Abstracts and reports from meetings were included only when they related directly to previously published work. Only papers published in English between 1990 and 2007 were included.

RESULTS

Recent retrospective analyses with bisphosphonates, and particularly with zoledronic acid, have shown significant correlations between biochemical markers of bone metabolism levels and clinical outcomes, especially for bone resorption markers. Clinical results for biochemical markers of bone formation and resorption and other emerging markers of bone metabolism including bone sialoprotein, receptor-activator of nuclear factor-kappaB ligand, osteoprotegerin, and other markers are presented. However, biochemical markers of bone metabolism are not yet an established surrogate endpoint for treatment efficacy.

CONCLUSIONS

Biochemical markers of bone metabolism may allow physicians to identify which patients with metastatic bone disease are at high risk for skeletal-related events or death and who may be responding to therapy. Prospective randomized clinical trials are underway to further assess the utility of markers of bone metabolism in patients with bone metastases.