In a similar line, transfection of human brain glioblastoma cells with Cx43 reduced proliferation in monolayer cultures and athymic nude mice, effects that were not associated with the establishment of gap junctional communication [565], and retroviral delivery of Cx43 and Cx26 to human breast tumor cells resulted in a reduction in tumor growth, with no detectable gap junctions nor rescue of intercellular communication [570]. Here, GJA1 is linked to neoplasm.