Validity of bone marker measurements for monitoring response to bisphosphonate therapy with zoledronic acid in metastatic breast cancer

Clinical utility of bone markers in various diseases

Measurements of bone markers (BMs) in peripheral blood or urine are a pivotal part of bone research within modern clinical medicine. In recent years the use of BMs increased substantially as they can be useful either to diagnose bone (related) disease and to follow its natural history, but also to monitor the effects of interventions. However, the use of BMs is still complicated mainly due to (pre)analytical variability of these substances, limited accessibility of assays, variable cut-off values in different countries and laboratories and heterogeneous results with regard to clinical implications of measuring BMs in several studies. This review will provide the clinician with a practical guide, based on current evidence, in which circumstances to test which bone markers for optimal diagnostic purposes, in order to improve patient care in different areas of bone diseases including Paget's disease, primary osteoporosis, tumor induced osteomalacia, hypophosphatemic rickets, van Buchem disease, chronic kidney disease, rheumatoid arthritis, neoplasma/multiple myeloma, type 2 diabetes mellitus and primary hyperparathyroidism. The clinician should consider fasting state, recent fractures, aging, menopausal status, concomitant liver and kidney disease when ordering and interpreting BM measurements as these factors might result in misleading BM concentrations. We found that BMs are clearly useful in the current diagnosis of tumor induced osteomalacia, van Buchem disease, Paget's disease and hypophosphatemic rickets. In addition, BMs are useful to monitor disease activity in chronic kidney disease, Paget's disease and are useful to monitor treatment adherence in osteoporosis.

Diagnostic accuracy of bone turnover markers as a screening tool for aseptic loosening after total hip arthroplasty

Aseptic loosening is the most common cause of prosthesis failure after total hip arthroplasty (THA). We measured serum cross-linked carboxyterminal telopeptide of type I collagen (ICTP), tartrate-resistant acid phosphatase 5b (TRAP5b), dickkopf-1 (dkk-1) and sclerostin; and urinary α isomer of C-terminal cross-linked telopeptide of type I collagen (αCTX-I) to investigate their potential diagnostic value detecting aseptic loosening after THA. Biomarkers were measured in 24 subjects with aseptic loosening of THA versus 26 control subjects without loosening after THA. Serum ICTP in the loose group (7.04 ng/mL) was higher than controls (5.15 ng/mL), (p = 0.0007). ROC analysis demonstrated that a serum ICTP >5.5 ng/L had a sensitivity of 91% and specificity of 69% for detecting aseptic loosening (area under ROC curve = 0.77, p = 0.0001), resulting in a positive predictive value (PPV) of 73% and a negative predictive value (NPV) of 90%. Serum TRAP5b in the aseptic loosening group (4.17U/L) was higher than controls (3.44 U/L), (p = 0.03). A serum TRAP5b >2.46 U/L had sensitivity of 100% and a specificity of 31% to detect aseptic loosening (AUC 0.67, p = 0.031), resulting in a PPV of 57% and a NPV of 100%. Serum dkk-1, serum sclerostin and urinary αCTX-I were not elevated in subjects with aseptic loosening (p>0.05). Serum ICTP and TRAP5b show potential utility as screening biomarkers for excluding aseptic loosening, because of their ability to discriminate individuals without disease. Our finding of elevated ICTP, generated by the action of matrix metalloproteinases, suggests a role for this group of endopeptidases in aseptic loosening.

RANKL: A promising circulating marker for bone metastasis response

Bone metastases are a frequent event in patients with solid tumors. Although great advances have been made in the treatment of these patients, the identification of novel, accurate indicators of bone response would greatly facilitate the clinical management of the disease. The receptor activator of nuclear factor-κB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) signaling pathway is significantly involved in bone metastasis formation. The main aim of the present study was to evaluate the role of circulating RANK, RANKL and OPG levels in predicting bone response. Marker accuracy was also compared with that of the conventional tumor marker N-terminal telopeptide of type I collagen (NTX). A prospective study was performed on 49 patients with bone metastases from breast, lung and prostate cancer, who were undergoing treatment with zoledronic acid. Patients were monitored for 1 year with blood tests, clinical evaluation and instrumental exams according to the response evaluation criteria of the University of Texas M. D. Anderson Cancer Center (Houston, TX, USA) and the Positron Emission Tomography Response Criteria in Solid Tumors. Circulating RANK/RANKL/OPG transcripts and NTX levels were evaluated by reverse transcription-quantitative polymerase chain reaction and immune enzymatic assay, respectively. The baseline RANKL levels differed significantly between responders and non-responders, whereas no differences in NTX levels were observed between the two groups. Receiver operating characteristic curve evaluation for all markers revealed that RANKL was the most accurate marker, with an area under the curve of 0.74 (95% confidence interval, 0.54-0.93). In addition, RANKL, which is the target of the novel monoclonal antibody denosumab, was the most accurate predictor of bone response in the present series of patients with bone metastases. Thus, the use of RANKL as a marker could potentially improve clinical practice, as current bone response evaluation is still somewhat problematic.

Procollagen assays in cancer

The synthesis rates of fibrillar collagens can be assessed in blood by measuring propeptides set free from corresponding procollagens before fiber formation. Type I collagen is the major component of the organic matrix of bone, but it is also found in other connective tissues. The serum concentration of the amino-terminal propeptide of type I procollagen, PINP, functions as a measure of type I collagen synthesis during normal bone turnover, but it is also released from bone metastases that involve an osteoblastic component. Type III collagen is a major constituent of soft tissues and the corresponding amino-terminal propeptide, PIIINP, reflects collagen synthesis. Circulating PIIINP tends to be affected by malignomas that grow in the peritoneal cavity or affect bone marrow. Many studies on procollagen markers in cancer have been cross-sectional or demonstrated treatment effects in patient groups. Markers that originate from bone turnover have wide reference intervals, but low biologic variability in individuals. Thus, they appear better suited for monitoring versus diagnostic purposes. There is still definite need for research on the use of procollagen markers in the followup of individual patients undergoing cancer treatment or being monitored after such treatment.