ERBB2 and neoplasm: Conversely, HCT/130-mono-mIL12 with moderate affinity for HER2 (KD ≈ 130 nM) and a much faster koff (18.9 × 10-3 s-1 or ~53 s) can deeply penetrate the distant regions in free form by repetitive cycles of HER2 binding and dissociation within the tumor interstitial space (Figure 6, step 2).