According to our previous studies showing that estrogens regulate c-Fos levels in diverse cancer cell types [41,42,43,44], the induction of c-Fos mRNA and protein expression upon a 4 h treatment with 100 nM E2 and 100 nM G-1 was abolished silencing GPER in SkBr3 cancer cells (Figure 5B,C) and CAFs (Figure 5D,E). This evidence concerns the gene GPER1 and cancer.