Photodynamic therapy (PDT) has drawn great interest in recent years mainly due to its low side effects and few drug resistances. Nevertheless, one of the issues of PDT is the need for oxygen to induce a photodynamic effect. Tumours often have low oxygen concentrations, related to the abnormal structure of the microvessels leading to an ineffective blood distribution. Moreover, PDT consumes O₂. In order to improve the oxygenation of tumour or decrease hypoxia, different strategies are developed and are described in this review: (1) The use of O₂ vehicle; (2) the modification of the tumour microenvironment (TME); (3) combining other therapies with PDT; (4) hypoxia-independent PDT; (5) hypoxia-dependent PDT and (6) fractional PDT.

Despite the exceptional progress in breast cancer pathogenesis, prognosis, diagnosis, and treatment strategies, it remains a prominent cause of female mortality worldwide. Additionally, although chemotherapies are effective, they are associated with critical limitations, most notably their lack of specificity resulting in systemic toxicity and the eventual development of multi-drug resistance (MDR) cancer cells. Liposomes have proven to be an invaluable drug delivery system but of the multitudes of liposomal systems developed every year only a few have been approved for clinical use, none of which employ active targeting. In this review, we summarize the most recent strategies in development for actively targeted liposomal drug delivery systems for surface, transmembrane and internal cell receptors, enzymes, direct cell targeting and dual-targeting of breast cancer and breast cancer-associated cells, e.g., cancer stem cells, cells associated with the tumor microenvironment, etc.

Photodynamic therapy is a therapeutic option to treat cancer and other diseases. PDT is used every day in dermatology, and recent developments in the treatment of glioblastoma, mesothelioma or prostate have demonstrated the efficacy of this modality. In order to improve the efficacy of PDT, different strategies are under development, such as the use of targeted PS or nanoparticles to improve selectivity and the design of light devices to better monitor the light dose. Due to the low penetration of light into tissue, another way to improve the efficacy of PDT to treat deep tumors is the use of upconversion NPs or bi-photon absorption compounds. These compounds can be excited in the red part of the spectrum. A relatively new approach, which we will call PDTX, is the use of X-rays instead of UV-visible light for deeper penetration into tissue. The principle of this technique will be described, and the state-of-art literature concerning this modality will be discussed. First, we will focus on various photosensitizers that have been used in combination with X-ray irradiation. To improve the efficacy of this modality, nanoparticles have been designed that allow the conversion of high-energy ionizing radiation into UV-visible light; these are potential candidates for the PDTX approach. They will be discussed at the end of this review.

Nanoparticles (NPs) have been shown to have good ability to improve the targeting and delivery of therapeutics. In the field of photodynamic therapy (PDT), this targeting advantage of NPs could help ensure drug delivery at specific sites. Among the commonly reported NPs for PDT applications, NPs from zinc oxide, titanium dioxide, and fullerene are commonly reported. In addition, graphene has also been reported to be used as NPs albeit being relatively new to this field. In this context, the present review is organized by these different NPs and contains numerous research works related to PDT applications. The effectiveness of these NPs for PDT is discussed in detail by collecting all essential information described in the literature. The information thus assembled could be useful in designing new NPs specific for PDT and/or PTT applications in the future.