CST4 and cancer: The relative abundances of 5 salivary gland proteins were significantly lower in the cancer group 6 months post treatment compared with the control group: Cystatin S, SA, SN, Cystein-rich secretory protein 3, Lactoperoxidase (Fig. 1a), Prolactin-inducible protein and Proline-rich protein 4 (Fig. 1b).