Substantial evidences suggested that the expression of Schwann cell hallmarks, including S100 calcium binding protein A4 (S100A4), p75 neurotrophin receptor (p75NTR) and glial fibrillary acidic protein (GFAP) were increased considerably in many tumors with PNI, such as melanoma [23], breast cancer [24], prostate cancer [25], colorectal cancer [26]. Here, S100A4 is linked to breast cancer.