We investigated the potential associations between genotypes of MDM2 SNP309 (rs2279744), SNP285 (rs117039649) and del1518 (rs3730485) and neutrophil counts in breast cancer patients receiving neoadjuvant sequential epirubicin and docetaxel, with additional G-CSF, in the DDP-trial (NCT00496795). This evidence concerns the gene CSF3 and breast cancer.