Increased primary breast tumor expression of CD73 is associated with development of bone metastases and is a potential biomarker for adjuvant bisphosphonate use

Abstract

Purpose: Increased CD73 expression has been associated with progression in various cancer types. Results of the AZURE and other trials suggest that, in postmenopausal breast cancer patients, adjuvant bisphosphonates inhibit bone relapses and prolong overall survival. Based on these findings, adjuvant bisphosphonates (typically zoledronic acid) are standard-of-care in postmenopausal patients with high-risk early breast cancer. However, biomarkers are needed for improved patient selection. The aim of this study was to investigate the association of primary tumor CD73 expression with later development of bone metastases.

Methods: To determine whether CD73 levels correlated with tumor parameters (hormone receptor status, tumor stage and grade), patient outcomes (bone metastases and survival) or other patient characteristics (menopausal status, chemotherapy or statin use), we analyzed primary breast tumor CD73 expression immunohistochemically in tumor microarray samples from the AZURE (BIG01/04) trial.

Results: In the AZURE control arm, high CD73 score are significantly prognostic for overall survival (p-value = 0.03, HR = 1.87, 95% CI = 1.06-3.29), disease-free survival (p-value = 0.06, HR = 1.66, 95% CI = 0.982-2.8) and time to first metastasis to bone (p-value = 0.04, HR = 2.23, 95% CI = 1.04-4.81), as compared with low CD73 scores. However, high CD73 score did not display an association with time to non-bone metastasis or first recurrence to a non-skeletal site. In the zoledronate arm, high CD73 score did not have association with patient outcomes, first metastasis to bone, nor with bone recurrence at any time (distant recurrence, including skeletal) or first non-skeletal recurrence. In multivariate testing, CD73 had no significant association with age, ER status, tumor stage, histological grade, menopausal status, chemotherapy or statin use in either arm.

Conclusions: High CD73 expression is associated with development of bone metastases. Zoledronate counteracts this effect. These results suggest that CD73 expression might serve as a biomarker for adjuvant zoledronic acid use.

Keywords: Bone metastases; Breast cancer; CD73; TMA.

Fig. 1

Representative images of immunostaining for CD73 in TMA cores from patients in the AZURE study. (A) Images of protein expression obtained using the anti-CD73 antibody and visualized at a magnification of 20x. Score 0–3 categories were determined by the intensity of staining in the cytoplasmic compartment of tumor cells only. Scale bar = 200 μm. (B) 40x magnification view of from the boxed regions depicted in panel A. Scale bar of core view = 100 μm. Scale bar of 40x = 50 μm.

Fig. 2

Prognostic value of CD73 levels in clinical events. Kaplan-Meier association of CD73 expression level in Overall Survival (OS) in (A) control and (B) zoledronic acid arms. Relationship between level of expression of CD73 in Disease-Free-Survival (DFS) in (C) control and (D) zoledronic acid arms. P-value is obtained from the log-rank test for testing quality of survival Q15 functions.

Fig. 3

Kaplan-Meier association of CD73 levels with clinical metastatic events. Relationship between CD73 expression to time to first bone recurrence, – where cancer spread to bone is the first recorded event in (A) control and (B) zoledronic acid arm. Relationship between level of CD73 expression to spread to bone at any time (for which patients may have had spread to non-bone sites first) in (C) control and (D) zoledronic acid arm. Relationship between CD73 expression to time to spread to non-bone sites in (E) control and (F) zoledronic acid arm. P-value is obtained from the log-rank test for testing quality of survival Q15 function.