Pre-clinical mouse studies blocking PTHrP with small-molecule inhibitors and neutralizing antibodies have shown promise in reducing metastatic disease across many types of cancers, including colorectal cancer [26], melanoma [27], squamous cell lung carcinoma [28], and breast cancer [28,29,30], but most efforts have focused on targeting the upstream regulators of PTHrP, including TGF-β, GLI2, matrix metalloproteinases (MMPs), and p38 MAP kinases [31]. This evidence concerns the gene PTHLH and breast cancer.