High Capacity of the Metastatic Breast Tumor Cells in Sphere Formation: Clue for Chemoresistance in Triple-Negative Breast Cancer

OBJECTIVE Metastasis is a major cause of cancer-related death in Triple-Negative Breast Cancer (TNBC). In TNBC, there is a significant correlation between metastasis and chemoresistance. Cancer relapse and metastasis are associated with the part of cancer cells with stem cell properties. These cancer stem cells are resistant to current cancer treatments. Due to their resistant nature, a significant relationship exists between the amount of cancer stem cells and chemoresistance. To our knowledge, to date, no comparative study was conducted on the number of these cells in metastatic loci vs. primary tumor site. METHODS In the present study, after developing a metastatic animal model of TNBC, metastatic and primary tumor cells were extracted from the lung and primary tumor of cancerous mice, respectively. In the next step, the sphere formation ability as a reliable in vitro assay to assess the presence and self-renewal ability of CSCs, in metastatic and primary tumor cells was evaluated separately. RESULTS The results showed that sphere formation ability, and consequently the population of cancer stem cells among metastatic tumor cells was significantly higher. CONCLUSION A higher percent of CSCs in lung metastatic site, compared with the primary tumor site, can partly explain the reasons for the chemoresistance and relapse in metastatic TNBC.