Fig. 1

Indirect interactions between mesenchymal stroma/stem cells and cancer cells. a Cytokines, chemokines, growth factors: MSC secrete a plethora of soluble factors that can bind as substrates to appropriate receptors on the cell surface of cancer cells and vice versa for mutual activation of signaling pathways. b Metabolites: Likewise, MSC-released metabolites such as prostaglandin E2, kynurenine or galectin-1 can act in a paracrine manner on cancer cells altering their properties and functions [14]. c Exosomes: Both, MSC and cancer cells, secrete exosomes for the exchange of small molecules including protein, mRNAs and microRNAs. d Microvesicles: Besides exosomes, microvesicles represent a different type of microparticles for the exchange of small molecules such as mRNAs or microRNAs affecting tumor cells and MSC in mutual ways