I already read literature about that but I can't find a good answer. For example, in Huang et al. 2010: "...hematoxylin staining reveal that the nontargeted (PEG-conjugated) gold nanorods are mainly localized around blood vessels, in the tumor stromal matrix, and inside some macrophage cells.... and the integrin- targeted (RGD-conjugated) nanorods are accumulated around tumor blood vessels (perivascular regions)." 

What is the stromal matrix, and what is the difference between the two intratumoral distributions. Thanks.