PDGFRB and cancer: On the other hand, for stromal cells targeting we used the 2′F-Py RNA Gint4.T aptamer (Kd, 9.6 nM; 33 nt) [20], which binds to the extracellular domain of platelet-derived growth factor receptor β (PDGFRβ), an established marker of stromal cells, including mesenchymal stem cells [30], cancer associated fibroblasts [31, 32], tumor-associated endothelial cells [33], immune cells [34, 35], and macrophages [36–38].