While the initial view was that PDE5 is highly expressed and can function in breast cancer cells, we show here that this enzyme is also upregulated in CAFs when compared to normal fibroblasts and this overexpression is a part of the dialogue between breast cancer cells and CAFs, allowing CAFs via CXCL16 secretion to promote breast cancer progression. The gene discussed is CXCL16; the disease is breast carcinoma.