ERBB2 and breast cancer: HER2 is overexpressed in ∼25% of all breast cancer cases and it is used to determine progression and prognosis.60, 61 Based on this, Berstad et al. in 201228 combined trastuzumab (Herceptin®)‐saporin and a chlorin photosensitiser to compare PDT versus PCI induced cell killing on either HER2+ or HER2− breast cancer cells.28 Light administration post exposure of cells to (Herceptin®)‐saporin in PCI was far superior in cell killing compared to PDT and the PCI light‐before treatment.