GCDFP-15 (gross cystic disease fluid protein 15), also known as PIP (prolactin-induced protein) is a secretory glycoprotein expressed in benign and malignant breast tumor tissues and in some normal exocrine organs such as sweat, salivary, and lacrimal glands.GCDFP-15 is a marker of apocrine differentiation and is frequently used for assessment of metastases or regional recurrences of breast origin.GCDFP-15 expression is increased by prolactin and androgen and inhibited by estrogen.
