Receptor activator of NF-kB (RANK) and RANK ligand protein expression in invasive ductal carcinoma.

Abstract

Abstract Abstract #2057 Purpose: Bone metastases are commonly observed in patients with advanced breast cancer. Tumor cells interact with the bone microenvironment to induce osteoclastogenesis via local bone stromal expression of receptor activator of NF-kB ligand (RANKL), leading to bone destruction and release of growth factors. In addition to its critical role in tumor-induced osteolysis, RANKL has been demonstrated to enhance the invasive behavior of epithelial tumor cells that express RANK, and RANK over-expression in transgenic mice using the breast-specific MMTV promoter results in increased mammary carcinoma. This study assessed the expression of human RANK and its ligand (RANKL) in invasive ductal carcinoma (IDC).
 Methods: We studied a total of 57 IDC specimens. Antibodies against human RANK (AF683) and human RANKL (M366; Amgen) were used for immunohistochemistry (IHC) cell staining along with an isotype control. The specificity of the 2 antibodies was substantiated by IHC, flow cytometry and Western blot analysis of positive and negative control cells. In addition, for RANK, mass spectrometry/protein sequencing of immunoprecipitated proteins was performed. The intensity of IHC staining was scored on a semiquantitative scale (1=weak, 2=moderate, 3=intense) or a complex scale (sum of percentages of stained tumor cells x staining intensity (0-3)).
 Results: Using a complex score with a threshold of 10, 20/57 IDC (35%) expressed minimal level of RANK (range 0 to <10, median 1) while 37/57 IDC (65%) expressed RANK protein with a score ranging from 10 to 100 (median 50). The expression in the tumor was heterogeneous, with cells having no expression and cells having intense expression. In addition, RANK was intensely expressed in the basal layer of all normal ducts and lobules. RANKL was observed in rare tumors (7/57; 11%), in rare lymphocytes of most tumor stroma (42/62; 68%), and in rare fibroblast-like cells in the stroma of rare tumors (3/62; 4.8%).
 Conclusion: In this study, RANK expression was observed by IHC in the majority (65%) of IDC. RANKL expression was observed in the epithelial carcinoma element of some tumors (11%) and was detected in 68% of tumors in rare lymphocytes infiltrating the tumor stroma. Correlation studies between prognosis markers ER, PR, Her2, and CK5/6 expression and RANK or RANKL expression in those IDC have been initiated. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2057.