Epithelial-mesenchymal transition and stem cell markers in patients with HER2-positive metastatic breast cancer

Currently, there is extensive information about circulating tumor cells (CTC) and their prognostic value; however, little is known about other characteristics of these cells. In this prospective study, we assessed the gene transcripts of epithelial-to-mesenchymal transition - inducing transcription factors (EMT-TF) and cancer stem cell (CSC) features in patients with HER2 ⁺ metastatic breast cancer (MBC). Epithelial cells were enriched from peripheral blood mononuclear cells (PBMC) using antibody-coated anti-CD326 antibody (CD326⁺) magnetic beads, and the residual CD326^- PBMCs were further depleted of leukocytes using anti-CD45 antibody-coated magnetic beads (CD326^-CD45^-). RNA was extracted from all cell fractions, reverse transcribed to cDNA, and subjected to quantitative reverse transcription PCR to detect EMT-TFs (TWIST1, SNAIL1, ZEB1, and TG2) as a measure of CTCs undergoing EMT (EMT-CTCs). In addition, PBMCs were analyzed using multiparameter flow cytometry for ALDH activity and CSCs that express CD24, CD44, and CD133. Twenty-eight patients were included in this study. At least one EMT-TF mRNA was elevated in the CTCs of 88.2% of patients and in the CD326^-CD45^- cell fraction of 60.7% of patients. The CD326^-CD45^- fraction of patients with elevated SNAIL1 and ZEB1 transcripts also had a higher percentage of ALDH⁺//CD133 ⁺ cells in their blood than did patients with normal SNAIL1 and ZEB1 expression (P = 0.038). Our data indicate that patients with HER2⁺ MBCs have EMT-CTCs. Moreover, an enrichment of CSCs was found in CD326 ^-CD45^- cells. Additional studies are needed to determine whether EMT-CTCs and CSCs have prognostic value in patients with HER2 ⁺ MBCs treated with trastuzumab-based therapy.