In contrast, HER2 low-expressing cells (MDA-MB231, MDA-MB468) maintained strong fluorescence intensity that was at the same level of intensity as the control cells, indicating that the NIR-PIT by HER2 Affibody–IR700Dye conjugate dramatically caused selective cell death of HER2-overexpressing breast cancer cells. The gene discussed is ERBB2; the disease is breast cancer.