Abstract P2-11-07: Proteins predictive of bone metastasis development in breast cancer patients
Authors: Westbrook JA , Cairns DA , Peng J , Speirs V , Hanby AM , Holen I , Marshall H , Banks RE , Selby PJ , Coleman RE , Brown JE 
Published: August 2014

Background

Bone is the commonest site of metastasis in breast cancer and bone metastasis is associated with skeletal complications and reduced quality of life. Adjuvant use of zoledronic acid (ZA) has been explored to prevent or reduce development of bone metastases. In the large international AZURE trial (N = 3360), early stage (II/III) breast cancer patients were randomised to standard therapy (control arm) or to standard therapy + ZA. There is an unmet need for biomarkers to identify early stage patients at high risk of developing bone metastasis so that therapy can be appropriately targeted. We report a study using proteomics and primary tumour tissue microarrays (TMAs) from patients in the AZURE trial to address this need.

Methods

Bone- and lung-homed variants of the MDA-MB-231 cell line were compared to the parental (non-bone homing) cell type using proteomics (difference gel electrophoresis and mass spectrometry) to identify differentially regulated proteins for clinical validation using TMAs from the AZURE trial. Following characterisation on breast cancer TMAs of different grade, protein expression of candidate biomarkers on AZURE TMAs was assessed semi-quantitatively (low, medium, or high) based on immunohistochemical staining intensity. Statistical analysis investigated associations between protein expression, clinical variables (e.g. ER/PR/HER2 status) and time to local and distant recurrence events (updated to 59 months follow-up).

Results

Over 140 proteins were differentially expressed and two were chosen for validation based on fold change, biological relevance and antibody availability: Macrophage-capping protein (CAPG) and PDZ domain-containing protein GIPC1. Cox proportional hazards regression analysis of 378 AZURE breast tumour samples showed that patients who did not receive ZA were 4.5-fold more likely to develop bone-only metastasis (p = 0.006) if both proteins were highly expressed in the primary tumour (adjusted for systemic therapy plan, ER status, lymph node involvement, Table 1). This effect was not seen in patients who received ZA. Kaplan-Meier analysis indicated that the effect was not linked to menopausal status.

Discussion

We have identified two proteins expressed in primary breast tumours of patients which are significantly associated with subsequent development of bone-only metastases and appear to predict for benefit from ZA. Biologically, the two proteins are reported to be involved in cellular structures and signalling, and are implicated in cancers, but their association with breast cancer bone metastasis appears to be novel. Ongoing analysis will extend validation in a further AZURE TMA sample set. These proteins have potential as biomarkers to predict development of bone metastasis.

Table 1: Cox proportional hazards regressions for breast cancer patients with high expression of CAPG and GIPC1 protein in primary tumour cells ArmN (events)HR95% CIp OV691.4520.673-3.1330.342Any distant recurrenceC341.2110.542-2.7040.641 ZA351.2400.468-3.2870.665 OV313.0361.150-8.0170.025Skeletal and other distant metastasesC172.9721.119-7.8890.029 ZA140.9780.214-4.4700.977 OV214.4461.547-12.7800.006Skeletal metastases onlyC144.4491.545-12.8080.006 ZA71.0560.122-9.1540.961Arm: OV, Overall, n = 378; C, Control, n = 191; ZA, n = 187

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-11-07.