Zhang et al calculated the microvessel density by CD31 staining, and there was a significant positive correlation between periosteal protein and the microvessel density observed by CD31 staining.[24] Kurokawa et al used CD31 immunostaining to analyze vascularization, and used computers to construct 3-dimensional images of microvessels in keloids and hypertrophic scars.[25] The same as VEGF, increased CD31 expression was also observed in radiated skin compared with the surrounding normal skin. Here, PECAM1 is linked to keloid.