ERBB2 and neoplasm: In the control groups, the tumor uptake of 99mTc-HP-Ark2 in the HER2-negative MCF7 (1.44 ± 0.08 %ID/g, P < 0.0001, n = 4) and MDA-MB-468 models (1.08 ± 0.06 %ID/g, P < 0.0001, n = 4) was significantly lower than that in the HER2-positive SK-BR-3 model, also indicating the specific targeting of the probe to HER2-positive tumors (Additional file 1: Figure S6).