In summary, having accounted for variables that might introduce bias in the results of the comparison of cytokine expression between post-surgical seroma samples derived from benign and malignant patients, three factors (GRO, ENA-78, TIMP-2) were found to be up-regulated (Fig. 2a) and five factors (IGFBP-1, IL-3, IFN-γ, FGF-9, IL-16) were down-regulated (Fig. 3a–c) in seroma fluid from breast cancer patients compared to non-cancer patients. This evidence concerns the gene FGF9 and breast cancer.