Serum Levels of Tartrate-Resistant Acid Phosphatase-5B in Breast Cancer Patients Treated with Pamidronate

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.

The use of molecular markers of bone turnover in the management of patients with metastatic bone disease

Biochemical markers of bone turnover are widely used in clinical practice. These indices have been shown to be associated with the occurrence, prognosis and therapeutic response of malignant bone lesions. For example, markers of bone resorption are often elevated in patients with established bone metastases and while this may point to a role of these markers in the diagnostic workup of cancer patients, the available evidence does not permit any final conclusions as to the accuracy and validity of the presently used markers in the early diagnosis of bone metastases. Many bone turnover markers appear to respond to antiresorptive and antineoplastic therapies, and recent evidence from prospective trials suggests that the aim of bisphosphonate therapy should be to normalize rates of bone remodelling to optimize therapeutic and prognostic outcomes. However, it remains unknown whether the use of bone markers in the routine clinical setting has any defined beneficial effects on overall outcome in cancer patients. Clearly, bone turnover markers have insufficient diagnostic or prognostic value to be used in isolation; however, the combination of these markers with other diagnostic techniques may improve clinical assessment of patients with bone-seeking cancers. This article reviews the available evidence (as of August 2007) on the clinical use of bone turnover markers in the management of patients with metastatic bone disease.

Can bone markers guide more effective treatment of bone metastases from breast cancer?

Bone metastases are a common problem for breast cancer patients, causing significant disease-related morbidity and mortality. Bisphosphonates and other cancer therapies can assist in managing these patients. However, assessing treatment efficacy in bone metastases is hampered by the inability to accurately measure disease response within a clinically desirable time frame. Bone-specific biochemical markers, notably type I collagen telopeptide cross-link by-products such as N-telopeptide (NTx) and C-telopeptide (CTx), have been shown to be effective tools for assessing the severity and extent of bone metastases, and the response to bisphosphonates. Elevated NTx levels correlate with adverse clinical outcomes. Normalization of NTx and CTx excretion rates are associated with relief of symptoms and a reduced incidence of skeletal-related events (SRE). This review discusses the expanding role of these bone markers in guiding treatment of bone metastases from breast cancer.

Clinical use of markers of bone turnover in metastatic bone disease

Bone metastases profoundly perturb normal bone remodeling. Biochemical markers of bone turnover have been shown to reflect these tumor-induced changes in bone remodeling and might therefore be useful in the diagnosis and follow-up of patients with malignant bone disease. Most markers of bone turnover, particularly those of bone resorption, are elevated in patients with established bone metastases. While this might indicate a role for bone markers as diagnostic tools in cancer patients, the available evidence does not provide any final conclusions as to the accuracy and validity of the markers presently used in the early diagnosis of bone metastases. Markers of bone resorption respond promptly and profoundly to bisphosphonate and antineoplastic therapy, and this response is associated with a favorable clinical outcome. Most markers, however, have been more useful in groups of patients monitored in clinical studies than in studies of individuals. While this makes them a good tool for drug development, it remains unknown whether the use of bone markers in a routine clinical setting has any defined beneficial effects on overall outcome in cancer patients. In particular, no study has addressed the question of whether patients with bone metastases should be treated according to their rate of bone turnover and what the treatment goals are in this respect. While it is unlikely that bone-turnover markers have sufficient diagnostic or prognostic value when used in isolation, the combination of these markers with other diagnostic techniques might be the way forward to improve the clinical assessment of patients with cancers of the bone.

Serum TRACP 5b is a useful marker for monitoring alendronate treatment: comparison with other markers of bone turnover

We studied clinical performance of serum TRACP 5b and other bone turnover markers, including S-CTX, U-DPD, S-PINP, S-BALP, and S-OC, for monitoring alendronate treatment. TRACP 5b had higher clinical sensitivity, area under the ROC curve, and signal-to-noise ratio than the other markers.

INTRODUCTION

The purpose of this study was to compare the clinical performance of serum TRACP 5b (S-TRACP5b) with that of other markers of bone turnover in the monitoring of alendronate treatment.

MATERIALS AND METHODS

This double-blinded study included 148 healthy postmenopausal women that were randomly assigned into two groups: one receiving 5 mg alendronate daily (n=75) and the other receiving placebo (n=73) for 12 months. All individuals in both groups received calcium and vitamin D daily. The bone resorption markers S-TRACP5b, serum C-terminal cross-linked telopeptides of type I collagen (S-CTX), and total urinary deoxypyridinoline (U-DPD), and the serum markers of bone formation procollagen I N-terminal propeptide (S-PINP), bone-specific alkaline phosphatase (S-BALP), and total osteocalcin (S-OC) were assessed at baseline and at 3, 6, and 12 months after initiation of treatment. Lumbar spine BMD (LBMD) was measured at baseline and 12 months.

RESULTS

Compared with the placebo group, LBMD increased, and all bone markers decreased significantly more in the alendronate group (p<0.001 for each parameter). The decrease of S-TRACP5b after first 3 months of alendronate treatment correlated significantly with the changes of all other markers except S-OC, the best correlation being with S-CTX (r=0.60, p<0.0001). The changes of LBMD at 12 months only correlated significantly with the changes of S-TRACP5b (r=-0.32, p=0.005) and S-CTX (r=-0.24, p=0.037) at 3 months. Based on clinical sensitivity, receiver operating characteristic (ROC) curves, and signal-to-noise ratio, S-TRACP5b, S-CTX, and S-PINP were the best markers for monitoring alendronate treatment. Clinical sensitivity, area under the ROC curve, and signal-to-noise ratio were higher for S-TRACP5b than for the other markers.

CONCLUSION

These results show that S-TRACP5b, S-CTX, and S-PINP are useful markers for monitoring alendronate treatment.

Tartrate-Resistant Acid Phosphatase 5b is a Useful Serum Marker for Extensive Bone Metastasis in Breast Cancer Patients

Purpose: Previous studies showed that serum tartrate-resistant acid phosphatase 5b (TRACP5b) activity was increased in 70% to 94% of breast cancer (BC) patients with bone metastasis (BM). This study aims to determine whether serum TRACP5b is useful for identifying limited or extensive BM in BC patients.

Experimental Design: Serum TRACP5b activity was measured in 168 BC patients, including 81 who were newly diagnosed with early BC, 20 with extraosseous metastasis, 24 with limited BM, and 43 with extensive BM. Serum TRACP5b activity was also measured monthly in 151 patients with early BC until they developed BM. Four hundred and twenty-seven (427) healthy women ages 18 to 90 served as control. One-way ANOVA was used to compare serum TRACP5b among groups. The sensitivity and specificity of serum TRACP5b as a marker for BM were estimated by receiver operator characteristic (ROC) curves.

Results: Serum TRACP5b increased with age in healthy women ( P &lt; 0.0001). It was significantly elevated in patients with extensive BM compared with all other groups ( P &lt; 0.0001). ROC analysis established a cutoff value of 4.026 units/L to identify patients with extensive BM with a specificity of 98% and a sensitivity of 93% (area under the curve = 0.9807; 95% CI = 0.9698-0.9915). Among the 151 patients with early BC, 6 developed limited BM and 2 developed extensive BM during the follow-up period. Serum TRACP5b remained below the cutoff value in patients with limited BM, but became significantly increased in those whose BM became extensive.

Conclusion: Serum TRACP5b activity is a useful diagnostic marker for extensive BM in patients with BC.

Assessment of therapeutic response in patients with metastatic bone disease

Metastatic bone disease is common in cancer patients and causes substantial disease-related morbidity and mortality. However, several effective treatments are available for the management of these patients. Bisphosphonates, which inhibit osteoclast-mediated resorption of bone matrix, are especially important because they decrease the incidence of skeletal-related events in many tumour types and can complement antineoplastic therapies. At present, assessment of treatment for bone metastases is hindered by a lack of effective, rapid methods to measure disease response. We discuss the difficulties of current measures of response assessment and describe the development of new radiological and biochemical markers of bone metastases. Assays that detect type I collagen telopeptides as markers of bone resorption seem to be most promising at present.