“…The PpIX converted from 5-ALA in fibroblasts was rapidly converted into heme by ferrous chelatase, which greatly reduces the effect of PDT. The lack of ferrous chelatase in cancer cells leads to a large accumulation of PpIX [25] . When the concentration of 5-ALA was greater than or equal to 2 mM, the PDT effect reached equilibrium, which agreed to the published research results [26] .…”