S100A4 and breast cancer: S100A4, also known as mts1, is a member of the S100 family of Ca2+-binding proteins and is thought to be directly involved in tumor invasion and metastasis via interactions with specific protein targets [19] in a variety of tumors, such as breast cancer [20, 21], gastric cancer [22], pancreatic cancer [23], colorectal cancer [24], non-small cell lung cancer [25], and prostate cancer [26].