A protein found on cells that line the lungs and reproductive organs, such as the ovaries. Human epididymis protein 4 may be found in higher than normal amounts in patients with some types of cancer, including ovarian epithelial cancer. Measuring the amount of human epididymis protein 4 in the blood may help plan cancer treatment or find out if cancer is getting worse or has come back. It is a type of tumor marker. Also called HE4.