MTR and neoplasm: An important issue is the difficulty to control the environment where Mφs are recruited which directly influences their phenotype and activity, and hence it might make the comparison of results from different studies inaccurate.[32] In this regard, there are concerns that Mφs being educated to induce antitumor effects turn into protumoral Mφs, influenced by the tumor microenvironment conditions and contribute to tumor survival.[33] Another concern is the in vivo biodistribution of Mφs and their homing capabilities.