ERBB2 and breast cancer: Martínez-Jothar et al. used two human breast cancer cells known as HER2-positive SkBr3 and HER2-negative MDA-MB-231, to show that PCI with the photosensitizer TPPS2a and saporin-loaded polyester nanoparticles could specifically target HER2-positive cells when the particles were functionalized with the nanobody 11A4, which binds to the HER2-receptor [27]; the antineoplastic drug saporin is a ribosome inactivating protein.