It is becoming increasingly evident that stromal cells such as macrophages, mast cells, adipocytes and mesenchymal cells associated with tumors significantly contribute to tumorigenesis. Some types of cancer indeed profoundly rely on extrinsic signals afforded by infiltrating or neighbouring cells for survival, proliferation and dissemination. Tissue disruption that results from tumor growth further activates tissue repair and inflammatory reactions that significantly shape the nature of the developing tumors. Over the past recent years, several studies have revealed that mesenchymal stem cells (MSCs) are recruited to tumors and play a particularly important role in the regulation of both solid and haematological malignancies. The tumor-homing properties of MSCs have further led to studies investigating their therapeutic use as targeted delivery vehicles of gene products. I hereafter discuss the role of MSCs in cancer.