ERBB2 and breast cancer: Taken together, our combination of NIR-PIT using the HER2 Affibody-IR700Dye conjugate and the trastuzumab-IR700Dye conjugate led to a strong anti-cancer effect for HER2-positive cancer cells, including HER2 low-expressing cells, trastuzumab-resistant cells, and brain metastasis of HER2-positive breast cancer.