GPER1 and breast cancer: While there has been no direct interactions described so far between GPER1 and COL17 at a molecular level, COL17 protein has already been shown to inhibit breast cancer cell proliferation and growth via decreasing the phosphorylation of key proteins in the AKT/mTOR pathway [92], which is known to be one of the major downstream signaling target of the GPER1 pathway as well [93–96].