CXCL12 and breast cancer: As some BP derivatives are able to induce mammary cancer cell proliferation, we performed RT-PCR to assay the ability of BP derivatives to induce the expression of several estrogen-regulated genes, focusing on two genes that are tightly linked with estrogen-mediated proliferation, the CXCL12 and amphiregulin genes [20]–[22] (Figs. 3.A and B).