Vitamin D receptor status of circulating tumor cells (CTC) in metastatic breast cancer patients

Objective: In recent years, several trials suggested that optimal vitamin D levels, by binding to the vitamin D receptor (VDR), have a protective effect against development of breast cancer. VDR expressed in breast tumors may have the potential to be a prognostic biomarker for breast cancer. The detection of circulating tumor cells (CTCs) predicts outcomes of early and metastatic breast cancers. The evaluation of VDR expression in CTCs of breast cancers patients may contribute to better characterize CTCs.

Material and methods: We developed an innovative triple fluorescence technique to visualize simultaneously cytokeratin, VDR, and CD45 on a single cell level. We compared VDR expression levels on various breast cancer cell lines and then on blood cytospins collected from 23 metastatic breast cancer patients.

Results: We could demonstrate very different expression levels of VDR in the 8 breast cancer cell lines, and even within one cell line. CTC analysis from patient blood samples was then performed with an individual assessment of VDR expression on each isolated tumor cell. We detected CTCs in 59.1% of the patients and demonstrated heterogeneities of the VDR status, aggregation and size.

Conclusions: We demonstrated that triple immunofluorescence allows an individual assessment of VDR expression at the protein level on CTCs in metastatic breast cancer patient. We plan to further explore if VDR expression relates to breast cancer subtypes classification, potentially as an independent prognostic and/or therapeutic biomarker factor.