GJA1 and breast cancer: This study was performed for the first two data sets: (1) SET 1 to analyse potential variations in Cx43 expression depending on the breast cancer subtype; and (2) SET 2 to discern possible differences in Cx43 levels in invasive breast cancer luminal B HER2- tissues according to their Oncotype DX Breast Recurrence Score Test results (Figs. 1 and 2 show representative IHC images).