BDNF and breast cancer: Previously, we have measured the BDNF level in the cultured media of different breast cancer cell lines (MCF-7, SK-BR-3, MDA-MB-231, MDA-MB-468) and the results showed that only MDA-MB-231 cells, but not other cell types, secreted BDNF into the culture media in a time-dependent manner (S3 Fig).