Abstract B95: PDL-1 is more frequently expressed on circulating epithelial tumor cells (CETCs) in metastatic than in non-metastatic breast cancer patients and could be a crucial factor in the inhibition of immune response to CETCs during metastasis formation

Abstract

Abstract Background: Analysis of CETCs is a promising diagnostic field for estimating the risk for metastatic relapse and progression. The phenotypic characterization of CETCs may provide real time information and can be of great value in therapy monitoring. Programmed cell death ligand 1 (PDL-1) is an important protein frequently upregulated in a number of different cancers. Cancer cells expressing PDL-1 inhibit immune-modulatory T-cell activation allowing disease progression. Therefore this immune checkpoint has emerged as an important target for immune therapy. The purpose of the current study was to identify potential patients who may benefit from PDL-1 targeted immunotherapies. Methods: CETCs were determined from blood of 22 (69%) non-metastatic and 10 (31%) metastatic breast cancer patients. The number of vital CETCs and the expression of PDL-1 were investigated using the maintrac® method. Results: PDL-1 expressing CETCs were detected in 94% of breast cancer patients; however the fraction varied between 30 to 100% in individual patients. There was no association between the frequency of PDL-1 positive CETCs and chemotherapy. Interestingly, we found a relationship between the frequencies of PDL-1 positive CETCs and progression of disease. Patients with metastatic disease had more PDL-1 positive CETCs as compared to patients without metastasis. Conclusion: Metastatic breast cancer patients have an elevated fraction of PDL-1 positive CETCs as compared to non-metastatic patients. These cells have the capacity to block the immune system and therefore may be a promising target for anticancer therapies. Monitoring the frequency of PDL-1 positive CETCs could contribute to individual patient's response for to anti-PDL-1 therapy. Citation Format: Monika Pizon, Dorothea Zimon, Ulrich Pachmann, Katharina Pachmann. PDL-1 is more frequently expressed on circulating epithelial tumor cells (CETCs) in metastatic than in non-metastatic breast cancer patients and could be a crucial factor in the inhibition of immune response to CETCs during metastasis formation. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B95.