An antigen expressed by tissues derived from mullerian epithelium (tubal, endometrial and endocervical) or celomic epithelium (mesothelial cells of the pleura, pericardium and peritoneum). Although its biochemical nature has not been clearly defined, CA125 has been described as a glycosylated, high-molecular-weight protein that may be released from damaged cells. Measurable in plasma, CA125 is a sensitive, nonspecific tumor marker for ovarian cancer; as such it is much more useful for monitoring clinical responses to the treatment of ovarian cancer than for the diagnosis of ovarian cancer. Elevated plasma CA125 may occur in association with other malignancies and non-malignant gynecologic disorders. (NCI04)