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Background: Gross cystic disease fluid protein (GCDFP-15), also called prolactin-inducible protein (PIP), is a single polypeptide chain with a versatile function in human reproductive and immunological systems (1). It is unique because of its small size (1). GCDFP-15 binds to CD4, exerts a potent inhibition on T lymphocyte apoptosis mediated by CD4/T-cell receptor (TCR) activation, and carries a fibronectin-specific aspartyl protease activity (2). Its ability to bind with other molecules like immunoglobulin G (IgG), actin, and zinc alpha2-glycoprotein (ZAG) shows its various biological activities (1). GCDFP-15 is expressed in benign and malignant human breast tumors and in normal exocrine organs such as sweat, salivary and lacrimal glands (1). It is up regulated by prolactin and androgens, while it is down regulated by estrogen (1). Due to its expression in breast cancer, GCDFP-15 is used as a prognostic biomarker (3, 4).