Prolactin inducible protein (PIP) is a 17-kDa glycoprotein present in human seminal plasma. PIP is synthesized as a 146-amino acid long polypeptide and shows high sequence similarity with mouse submaxillary gland with a single glycosylation site. PIP is known variously as gross cystic breast cyst fluid protein-15 (GCDFP-15), a marker of human primary and metastatic apocrine breast carcinomas, or gp 17/secretory actin binding protein (SABP)/extra-parotid glycoprotein (EP-GP), a secretory glycoprotein isolated from seminal vesicles, salivary glands and sweat glands The exact biological functions of PIP are still uncertain but various functions have been assigned to PIP due its occurrence at high concentration in biological fluids. PIP binds to many proteins such as fibrinogen, actin, keratin, myosin and tropomyosin. PIP is expressed in pathological conditions of the mammary gland and in several exocrine tissues, such as the lacrimal, salivary,and sweat glands. Because of its association with secretory cell differentiation, PIP has been used in diagnostic evaluation of tumors of breast, salivary gland, and skin.