ABCB1 and neoplasm: found that methylene blue-mediated PDT combined with the chemotherapeutic drug adriamycin (DOX) exhibited potent cytotoxicity against drug-resistant tumor cells due to the presence of drug-resistant cells after PDT therapy high concentrations of DOX, along with a decrease in P-glycoprotein expression and an increase in reactive oxygen species yield in tissues, which ultimately led to necrosis or apoptosis of drug-resistant tumor cells (69).