Mesenchymal Stem Cell-Breast Cancer Stem Cell: Relevance to Dormancy

Clinical advancement in cancer treatment has improved patient's outcome. Despite these advancements, cancer continues to remain amajor clinical problem.However, treatment has been hindered by the ability of cancer to remain dormant for later resurgence. This review discusses dormant breast cancer (BC) with an emphasis on cancer stem cells (CSCs). BC cells (BCCs) havepreference for thebonemarrow (BM).Wediscusshowcells of theBMmicroenvironment suchasmesenchymal stem cells (MSCs) and the hematopoietic supporting stroma interact with CSCs to support the latent or dormant phase of CSCs. The exchanges of small non-codingmicroRNAs between theCSCs andBMmicroenvironmental cells to induce cycling quiescence in CSCs are discussed. The article proposes the implications for treatments of BCCs and the challenges to target these cells in organs suchasBM.Part of the challenges in this article include the similarity between theCSCsand the endogenous normal stem cells. The role of BM microenvironment with regards to oxygen levels and the ability to release cytokines as support of tumor growth is incorporated in the review.