For example, in vitro studies have demonstrated an enhanced PpIX accumulation in the tumor tissues and a complementary increase in the efficacy of PDT following the upregulation or presence of ATP-binding cascade (ABC) transporters inhibitors [222], iron chelators [223], calcitriol [224], arsenic trioxide [225], or NF-kappaB inhibitors [226]. Here, ABCG2 is linked to neoplasm.