Epithelial‑mesenchymal transition was identified as a potential marker for breast cancer aggressiveness using reverse transcription‑quantitative polymerase chain reaction.

The primary cause of breast cancer‑associated mortality is the formation of distant metastasis. During the metastatic process, single tumor cells dissolve from the primary tumor site and undergo various changes in cell adhesion and motility properties. The tumor cells invade the blood stream and travel to different sites of the body, where they may initiate outgrowth. These cells are referred to as circulating tumor cells (CTCs). The process of changing cellular properties is known as epithelial to mesenchymal transition (EMT). As a different set of genes is upregulated during EMT, such genes may serve as marker genes for the detection of CTCs based on reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). Therefore, EMT‑ and breast cancer‑related genes were selected as RT‑qPCR markers. These genes were tested for performance in a model system of blood samples from healthy donors, to which a number of various breast cancer cell lines were added. The genes with optimal performance were subsequently used in RT‑qPCR with 35 breast cancer patient samples. The genes which showed the highest and most consistent increase in gene expression with the increase in the number of cancer cell line cells added were CK19, Snail, FoxC2 and Twist. Following RT‑qPCR for all patient samples, two subgroups were arranged: One group in which all genes were downregulated and the second group with at least one gene indicated an upregulation of gene expression. Comparisons were made between the tumour characteristics from these two groups. Results suggested that carcinomas of the first group exhibited a less aggressive tumor biology compared with those in the second group. The present study indicated a novel RT‑qPCR based test for tumor malignancy.