Among the nine selected tumor-suppressing protein candidates that were enriched in lymphocyte-derived iTSC CM, five of them, including Uba1 (ubiquitin-like modifier activating enzyme 1), SNRPE (small nuclear ribonucleoprotein polypeptide E), OXCT1 (3-oxoacid CoA-transferase 1), S100A9 (S100 calcium-binding protein A9), and PABPC1 (polyadenylate-binding protein 1), reduced MTT-based viability of MDA-MB-231 breast cancer cells. Here, S100A9 is linked to breast cancer.