Metastatic breast cancer detection and therapy monitoring using folate-targeting flow cytometry.

Abstract

23 Background: Circulating tumor cell (CTC) has emerged as a valuable surrogate tumor marker for cancer diagnosis, prognosis, therapy personalization, and drug discovery. To identify CTCs, EpCAM and/or cytokeratin have been commonly used; however, their expression may diminish for subgroups of breast cancers or during epithelial-mesenchymal transition. A unique approach by targeting folate receptor (FR) on CTCs overcomes the limitation. Cancer cells overexpress FR with high affinity (KD=0.1 nM) to internalize high levels of folate for rapid growth. FR is also found upregulated in most cancers, while at very low levels in normal tissues. Methods: A flow cytometry based in-vitro CTC assay kit (OncoIVDx) was developed by IV Diagnostics Inc to specifically enumerate CTCs which overexpress FRs. 20 mL of 9 metastatic breast cancer (MBC) patients' peripheral blood was collected using CellSave tube before and after the treatment in midst of therapy. CTCs were tagged by fluorescently labeled folate conjugate, while leukocytes were counterstained by anti-CD45. To absolutely count the rare CTCs, a fluorescent bead was added serving internal control. Results: Table. Conclusions: No obvious shift in dot plots was found for patients' leucocytes compared to those in normal sample. Tumor size, histologic grade, nodal involvement and lymphovascular invasion (LVI) did not display a significant association with CTC presence, although more positive nodes with identified LVI might indicate an unfavorable increase in CTC counts. CTC presence was found associated with serum marker CA27.29. A score of 30 and less correlated with CTC response to the treatment. Chemotherapy alone or in combination with hormone therapy did not correlate with the change in CTC counts after treatment, except for hormone therapy alone. Unfavorable progression of cancers could be predicated for the patients with approximately 25 and more CTCs. We would like to thank NIH/NCI for SBIR phase I grant (1R43CA13789301A1). [Table: see text]