More recently, it was shown that metastatic 4T-1 breast cancer cells form functional GJs with EC via Cx43 and that Cx43 expression is required for metastatic breast cancer cell extravasation and blood vessel co-option in the brain, while metastatic melanoma B16 cells use Cx26 for brain perivascular microtumor formation [130]. This evidence concerns the gene GJB2 and breast cancer.