Moreover, a clinical study by Koukourakis et al. revealed that esophageal tumors with high intratumoral protein levels of HIF-1 were more resistant to PDT compared to tumors with low HIF-1 protein levels [327], attesting to the involvement of HIF-1-mediated survival pathways following PDT (Section 3.3.2 and Fig. 5). Here, HIF1A is linked to neoplasm of esophagus.