Given the similarities between PTHrP overexpression in PyMT tumors and this model of secretory carcinomas, as well as the fact that PTHrP has been shown to activate AP1 signaling by increasing c-fos and/or JunB expression in several cell types, further study of potential interactions between PTHrP and AP1 signaling in breast cancer may be revealing [82, 83]. Here, FOS is linked to breast cancer.