Expression of the calcium receptor in human breast cancer—a potential new marker predicting the risk of bone metastases R. Mihai a, * , J. Stevens b , C. McKinney b , N.B.N. Ibrahim b a Department os Surgery, University of Bristol, Bristol BS2 8HW, UK b Department of Pathology, Frenchay Hospital, Bristol, UK Accepted 8 February 2006 Available online 24 March 2006 Abstract Aims: This study investigates whether the calcium-sensing receptor (CaR) is commonly expressed in primary breast cancers. The CaR controls secretion of PTHrP in several breast cancer cell lines and PTHrP is known to stimulate osteolysis during metastatic bone resorption. Whether this could explain the propensity of breast cancers to develop bone metastases has not been explored. Methods: With Ethical Committee approval, immunohistochemistry was performed using a commercially available antiCaR antibody (AffinityBioReagents, Cambridge, UK) on archived histological sections of primary tumours from patients who died with advanced breast cancer. Intensity of CaR expression was assessed by two independent observers on a 6-point scale. Results: One hundred and eight patients with breast cancer were found to have positive bone scans, 42 patients had died. Of the patients with negative bone scans, 23 had liver or lung metastases. Most patients with strongly expressed CaR (score 4–5 on immunohistochemistry) had bone metastases (13/15 patients) compared with 2/23 patients with normal bone scans (p!0.001, c 2 test). Other clinical/pathological markers (ER, PR, c-erb B-2, LN status) were not significantly different between patients with CaR-positive or CaR-negative tumours. Conclusions: CaR expression is common in a selected group of patients with advanced primary breast cancers. A prospective study should investigate if patients with CaR-positive tumours are more likely to develop bone metastases. q 2006 Elsevier Ltd. All rights reserved. Keywords: Calcium-sensing receptor; Breast cancer; Bone metastases Introduction The plasma membrane calcium-sensing receptor (CaR) was cloned from parathyroid cells 1 and was shown to represent the main component of the calcium-sensing mechanism involved in the inhibition of parathyroid hormone (PTH) secretion during hypercalcaemia [reviewed in Ref. 2]. More recently, CaR expression has been demonstrated in a variety of tissues and cells not involved in calcium homeostasis and it became apparent that CaR stimulates cell proliferation in several cell types. 3–6 Important for the hypothesis developed in this study, normal human breast tissue and ductal carcinomas express CaR. 7 Furthermore, human breast cancer cell lines MDA-MB-231 and MCF-7 express CaR and its stimulation leads to increased PTHrP secretion from these cell lines. 8 Similarly, PTHrP production and calcium transport in mammary epithelial cells are regulated by extracellular calcium acting through the CaR. 9 Parathyroid hormone-related protein (PTHrP) is a tumour product with the ability to activate PTH receptors. Secretion of PTHrP by tumoural cells drives osteolysis by osteoclasts, leading to release of growth factors and calcium from the bone matrix and further stimulation of tumoral cell proliferation. 10 Furthermore, there is a positive correlation between the levels of PTHrP expression in primary breast cancers and the subsequent risk of developing skeletal metastases 11 and PTHrP expression in skeletal metastases is more frequent and at higher levels than in the primary breast cancers. 12,13 The hypothesis that triggered this study is that CaR expression acts as a selection mechanism for tumour cells EJSO 32 (2006) 511–515 www.ejso.com 0748-7983/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ejso.2006.02.009 Abbreviations CaR, calcium-sensing receptor; ER, oestrogen receptor; IHC, immunohistochemistry; PTH, parathyroid hormone; PTHrP, para- thyroid hormone-related peptide. * Corresponding author. Tel.: C44 1865 220924; fax: C44 1865 220925. E-mail addresses: r_mihai99@hotmail.com (R. Mihai), jonathan. stevens@nbt.nhs.uk (J. Stevens), charles.mckinney@nbt.nhs.uk (C. McKinney), nassif.ibrahim@nbt.nhs.uk (N.B.N. Ibrahim).