Several studies reported that APN/CD13 is overexpressed in the endothelial cells of tumor vasculature and in several solid tumors, such as melanoma [18, 19], prostate carcinoma [20], lung cancer [21], pancreas adenocarcinoma [22], ovarian cancer [23], breast cancer [13], colon cancer [24], thyroid cancer [25], and fibrosarcomas [26]. Here, ANPEP is linked to breast cancer.