The combination of NIR-PIT using the HER2 Affibody-IR700Dye conjugate and the trastuzumab-IR700Dye conjugate enhanced the cytotoxic effect for HER2-positive breast cancer cells, including HER2 low-expressing cancer cells, trastuzumab-resistant cancer cells, and brain metastatic cells. This evidence concerns the gene ERBB2 and breast carcinoma.