Methods: The involvement of P-glycoprotein (P-gp/ABCB1), breast cancer resistance protein (BCRP/ABCG2), and multidrug resistance-associated protein 1 (MRP1/ABCC1) in the transport of 7 clinically utilized photosensitizers [benzoporphyrin derivative (BPD), temoporfin, redaporfin, talaporfin sodium, rose bengal, methylene blue, and indocyanine green] were investigated using human breast cancer cell lines following well-established protocols. Here, ABCG2 is linked to breast cancer.