Predictive value of osteocalcin and β-CrossLaps in metastatic breast cancer

Abstract

Objectives:

Assessment of the diagnostic value of serum CEA, CA 15.3, osteocalcin (OC) and β-CrossLaps (β-CTX) in the detection of metastatic breast cancer.

Design and methods:

This study included 47 patients with breast cancer (20 non-metastatic breast cancer, 11 bone metastasis, 11 soft tissue metastasis, 5 bone plus soft tissue metastasis), 10 patients with benign breast lesions and 13 healthy volunteers. CEA and CA 15.3 were determined using microparticle enzyme immunoassay; while OC and β-CTX were measured by electrochemiluminescence immunoassay.

Results:

CEA, CA 15.3, OC and β-CTX median levels were higher in breast cancer patients compared to controls (p = 0.006, 0.001, 0.004 and 0.038, respectively). Increased levels of OC and β-CTX were demonstrated in bone metastatic patients compared to non-metastatic or soft tissue metastatic patients (p = 0.000).

Conclusions:

Combined use of OC and β-CTX could be useful in early detection of bone metastatic breast cancer which might improve the outcome of the disease.

Introduction

Breast cancer is the third most common cancer in the world. Each year, almost 800,000 women are diagnosed with breast cancer worldwide. Breast cancer-associated bone metastases remain a common cause of morbidity and mortality. After metastatic bone disease is diagnosed, life expectancy is approximately 20 months. Bone lesions, which occur in an estimated 65% to 75% of patients with advanced metastatic breast carcinoma, may lead to skeletal-related events (SREs), including pathologic fracture, surgery to bone, spinal cord compression, debilitating bone pain requiring strong narcotics or palliative radiotherapy and potentially life-threatening hypercalcemia of malignancy [1]. Elucidation of the cellular and molecular mechanisms by which breast cancer selectively spreads to bone is essential for the development of mechanism-based effective and specific therapeutic interventions for this deleterious complication in breast cancer. CEA and CA 15.3 are the serum tumor markers commonly used for post-operative monitoring of breast cancer [2].

In the process of bone metastasis, the primary mechanism responsible for bone destruction is cancer cell-mediated stimulation of osteoclastic bone resorption, which results in osteolysis and release of various growth factors from the bone matrix. These growth factors are prerequisites for successful colonization and subsequent invasive growth of cancer cells in bone, thus establishing a “vicious cycle” [3], [4]. The diagnosis of bone metastases usually relies on skeletal X-ray and bone scintigraphy. This latter technique is a sensitive diagnostic tool but lacks specificity [5]. Several biochemical markers of bone formation and bone resorption have been developed in order to help the clinician in the diagnosis and follow-up of bone metastases. Among these markers, bone-specific alkaline phosphatase (B-ALP), procollagen I C-terminal propeptide (PICP), procollagen I N-terminal propeptide (PINP) and osteoclacin (OC) reflect bone formation, while type I collagen C-telopeptide (ICTP), C-terminal cross-linked telopeptide of type I collagen (CTX), N-terminal cross-linked telopeptide of type I collagen (NTX), pyridinoline (Pyr) and deoxypyridinoline (D-Pyr) represent degradation products of mature collagen and reflect bone resorption [6].

Osteocalcin is a 5.8-kDa, hydroxyapatite-binding, protein exclusively synthesized by osteoblasts, odontoblasts and hypertrophic chondrocytes. One of the major characteristics of OC is the three vitamin-K-dependent, gamma-carboxyglutamic acid residues, which are responsible for the calcium binding properties of the protein. After release from osteoblasts, the largest part of the newly synthesized protein is incorporated into the extracellular bone matrix where it constitutes approximately 15% of the non-collagenous protein fraction and a smaller fraction is released into circulation [6], [7]. OC is readily subjected to rapid degradation in serum, so that both intact peptides and OC fragments of various sizes coexist in the circulation. Only one third of the total OC serum pool represents intact OC (amino acids 1–49). A third is represented by a large N-terminal mid-molecule (N-MID) fragment of 43 amino acids and another third by several small fragments [5].

Type I collagen consists of two α1 chains and one α2 chain. The intact C-terminal telopeptide α1 chain consists of a 26 amino acid sequence. The amino acid sequence EKAHDGGR comprises a DG-motif (positions 19–20) susceptible to post-translational modifications. In newly synthesized collagen, a native non-isomerized form (Asp-Gly) denoted α-CTX is represented. However, with increasing age of bone, an isomerized form (βAsp-Gly) denoted β-CrossLaps (β-CTX) is formed. Furthermore, the lysine residue (K) participates in inter-molecular cross-links in mature bone [8], [9].

Despite early indications of a correlation between some bone marker levels and clinical outcome, the available data do not allow any final conclusions to be drawn about the validity of any of these markers in the primary diagnosis of bone metastases [10]. The aim of the ongoing work is to determine the diagnostic efficacy of serum CEA, CA 15.3, OC and β-CTX in detection of bone and/or soft tissue metastases in breast cancer patients.