Overall, these results indicate that Day 13‐expanded NK cells (TS‐NK) exhibit promising cytotoxic potential against solid tumors, particularly HER2‐positive breast cancer (SK‐BR‐3, BT‐474), breast cancer (MDA‐MB‐231), liver cancer (PLC/PRF5), lung cancer (A549) and gastric cancer (AGS) (Figure 4e). Here, ERBB2 is linked to breast cancer.