ESR1 and breast cancer: Moreover, CCN5 expressing BC cells arealways ER-α positive, while CCN5 expression is lacking in HER-2/Neupositive and triple-negative BC (TNBC) cells.25,27, 28, 29, 30, 31 Ectopic CCN5 expression augments ER-αexpression in ER-α-negative BC cells.25,32 Collectively, these studies implicate afine tune between CCN5 signaling and ER-α pathways in BCs.