PECAM1 and neoplasm: We further characterized the microvessels with anti‐CD31, which can specifically react with CD31, a marker protein in the vascular endothelial cells,[50] and found that the fluorescence of ICG was not completely colocalized with the one of the tumor microvessels (Figure 5b), implying that ICG‐PtMGs@HGd could extravasate from the microvessels and penetrate into the deeper part of the tumors, and would therefore achieve a better phototherapeutic efficacy.