Intercellular Communication by Exosome-Derived miRNAswithin The Tumor Microenvironment in Breas t Cancer

The process of tumor formation and progression is influencedby two factors, namely genetic/epigenetic changes in the tumorcells and the rearrangement of the components of the tumor microenvironment(TME) through mutual and dynamic cross talk.TME consis ting of dis tinct cell types including s tromal cellsand immune cells has recently emerged as a pivotal player intumor development and progression. Over the las t decade, researchershave demons trated that mesenchymal s tromal/s temcells (MSCs) can also migrate to the tumor microenvironment.Even though there has been an intense interes t in the role ofMSCs in cancer progression, the relationship between MSCsand tumor cells remains open to debate. Several s tudies havesugges ted that MSCs contribute to tumor progression and metastasis, whereas other reports have shown that MSCs suppresstumor growth. MSCs have been shown to be involved in theformation and modulation of tumor s troma and in interactingwith tumor cells, partly through their secretome. Exosomes arenano-sized intraluminal multivesicular bodies secreted by mos ttypes of cells and have been found to mediate intercellular communicationthrough the transfer of genetic information via codingand non-coding RNAs to recipient cells. Since exosomesare considered as protective and enriched sources of shuttle microRNAs(miRNAs), we hypothesized that exosomal transferof miRNAs from MSCs may affect tumor cell behavior, particularlyangiogenesis. However, molecular mechanisms underlyinginteractions between MSCs and tumor cells in breas t cancerprogression need to be thoroughly elucidated, which may provideattractive targets for making promising novel s trategies forbreas t cancer therapy.