**2. Expression of HE4 in tumours**

HE4 is a secretory glycoprotein. It is over-expressed in ovarian carcinomas especially in serous and endometriod variants. It is also called whey-acidicprotein that belongs to WAP domain family. WAP is a four-disulfide core domain protein 2 [WFDC2]. It was initially described to have tissue specific expression in epididymis [5].

Available literature revealed that HE4 is expressed in female reproductive tract, breast tissue, kidney, regions of the respiratory tract and nasopharynx [6–8]. Moreover, it is also expressed in normal human trachea, salivary glands, lung, prostate, pituitary gland, thyroid, and kidney [8]. It's an independent prognostic marker in non-small cell lung cancer [NSCLC] [9].
