Abstract P3-02-06: Correlation of BCL-2 and Apoptosis on Circulating Tumor Cells and Breast Cancer Tissue

Abstract

Abstract Background: Circulating Tumor Cell (CTC) levels are prognostic markers in metastatic breast cancer (MBC). Further phenotypic characterization of CTC may provide an opportunity for non-invasive evaluation of predictive and prognostic markers. Apoptosis is a common form of chemotherapy-induced cell death. Monoclonal antibody (MAb) M30 recognizes a neo-epitope on fragmented cytokeratin and is a marker of apoptosis. BCL-2 is an anti-apoptotic marker and may predict for resistance to anti-neoplastic therapy. We have previously reported the results of a pilot clinical trial to estimate M30 and BCL-2 expression in CTC from patients with MBC. The current study was performed to correlate the expression of both BCL-2 and M30 in CTC with breast cancer tissue samples. Methods: Of the 85 patients in the original pilot study, 52 (61%) had evaluable tissue available (39 primary and 12 metastatic lesions; one unknown) and were included in this analysis. CTC were collected at baseline and were isolated, enumerated, and phenotypically characterized for M30 and BCL-2 using the CellSearch® System. CTC phenotype is reported as percentage of cells with positive staining. Tissue Microarrays (TMA) were constructed and immunohistochemically stained for M30 (anti-Cytodeath™ M30, Roche) and Bcl-2 (M-0887, DAKO) and scored using the Allred method. Results: Tissue staining for M30 and Bcl-2 were inversely correlated. Of the 52 patients with TMA available for investigation, 22 (42%) had > 5 CTC/7.5 ml whole blood. A positive, but non-significant, correlation was observed between increasing numbers of CTC levels and tissue BCL-2 Allred Score (Spearman r=0.36; p=0.1310). M30 staining was detected in ≥10% of CTC in 20 of the 22 (91%) patients with elevated CTC, while BCL-2 staining was detected in ≥10% of CTC in 19 of the 22 (86%) patients. Little if any correlation was observed between CTC M30 and tissue M30 expression, however CTC BCL-2 was positively correlated with tissue Bcl-2 expression (Spearman r=0.47; p=0.0440). Conclusions: BCL-2 and M30 can be characterized in both CTC and breast cancer tissue. The likelihood of having elevated CTC may be associated with higher BCL-2 expression, and CTC BCL-2 was associated with tissue BCL-2 expression. Although the clinical implications of these findings are unknown, they offer the opportunity for future trials to investigate whether CTC BCL-2 and M30 might be useful to identify patients with cancers that are resistant to standard therapies. Furthermore, CTC BCL-2 and M30 might be monitored in clinical trials of novel, apoptosis-inducing therapeutic agents. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P3-02-06.