With antibodies targeting the last 20 amino acids of the Cx43 C-terminal tail (see Additional file 1: Methods and Additional file 2: Figure S1), we detect GJA1-20k in a wide variety of cell lines derived from different cancers including cervical cancer (C33a), lung cancer (A549 and Hop-62), breast cancer (BT-549 and MDA-MB-231), endometrial adenocarcinoma (Ishikawa), and mouse embryonic carcinoma (NF-1) (Figures 1a and 2b). This evidence concerns the gene NF1 and breast cancer.