The role of radiotherapy-resistant stem cells in breast cancer recurrence.

Abstract

Although the effectiveness of anti cancer therapies has improved dramatically, breast cancer (BC) remains the second leading cause for cancer-related death among women in the western world [1]. The observed improvement in the survival rate and remission for primary tumors are essentially related to the advances in early diagnosis with more sensitive imaging technology [2,3]. However, the death rate remains unacceptably high for BC patients due to hard-to-treat metastatic and recurrent tumors, necessitating new, effective approaches and anticancer agents. Accumulating evidence suggests that cancer stem cells (CSCs), which are present in many cancers including BC, mediate tumor metastasis and contribute to relapse due to their resistance to current conventional therapies [4,5]. These unique cells possess stem cell-like characteristics, such as the capacity of self-renewal, which makes the tumor capable of regenerating its entire bulk. CSCs are resistant to proapoptotic factors, rendering them a formidable adversary to anticancer agents. In part, this is related to their quiescence capacity, which holds them in a standby mode in their niche microenvironment, sheltering them from radiation and other anticancer agents, since these agents are effective only on highly proliferative cells [6,7]. In addition to their powerful DNA repair machinery, breast CSCs (BCSCs) express ALDH, which is suspected to play a part in their death-resistance phenotype by being involved with cell detoxification machinery [8,9]. Thus, BCSCs represent a major challenge in the battle against BC, and an opportunity to develop more effective target to treat metastatic lesions.