Development of drug resistance due to overexpression of efflux transporters such as P‐glycoprotein (P‐gp) can limit the clinical therapeutic outcomes of chemotherapy.224 Photosensitizers such as methylene blue may be able to inhibit P‐gp mediated drug efflux and this was independent of PDT effect, as methylene blue without light can counter the drug resistance of Dox in cell lines.225 Nanoparticles combining two treatment modalities using Dox and methylene blue can potentially overcome tumor drug resistance. The gene discussed is PGP; the disease is neoplasm.