The quantification of CXCL12 in cell-conditioned media (Figure S1B) indicates that all BC lines secrete different levels of this chemokine, although these do not overall correlate with the extent of internalized receptors, thereby suggesting that other signaling components in BC cancer cells might contribute to shape a steady-state pool of intracellular receptors. The gene discussed is CXCL12; the disease is breast cancer.