The implantation of adult mesenchymal stem cells (MSCs) has become a promising alternative in cancer treatments. Accordingly, in this article we revised the ultimate advances in the knowledge on the MSC-homing mechanism, the cancer cell and MSCs interactions and the microvesicles and exosomes used by malignant cells to transport and deliver pro-cancer cytokines or microRNA (miRNA), or by MSCs to favor or fight cancer progression. In addition, we analyzed the current knowledge generated by ongoing or terminated preclinical and clinical trials, using naive MSCs as natural anti-cancer living factors or gene-engineered MSCs as cytokine delivering vehicles, where anti-cancer cytokines were chosen and the pro-cancer factors were avoided. Finally, we present some concerns about the implantation of MSCs and anti-cancer therapies and hypothesize the MSC implantation combines with conventional or new therapies to treat cancer.