S100P and breast cancer: For subgroup analysis (Figures 5D–M), S100P in HER2+ tumor tissue decreased by 57.58% after chemotherapy (p = 0.027, Figure 5B), while there was no statistical difference in the change of S100P in the HER2− subgroup (p = 0.942, Figure 5C), which suggested that HER2+ breast cancer cells with higher levels of S100P were more sensitive to chemotherapy.