The anti-tumor effect induced by PDT in MDR cancers may result from the following: 1) inhibiting some anti-apoptotic proteins, such as those in the Bcl-2 family [41], 2) preventing a drug-efflux effect, damage to ATP-binding transporters [42], 3) altering the microenvironment of tumor cells, including by microvascular injury and inflammatory factor secretion [43, 44], 4) enhancing the permeability of tumor vessels and promoting drug delivery [43, 45], and 5) promoting immune system response [46]. The gene discussed is BCL2; the disease is neoplasm.