The tumor marker CA 125 is a common constituent of normal cervical mucus

The presence of the tumor marker CA 125 was studied in the cervices of healthy women. Immunohistochemical staining of normal cervical tissue demonstrated the presence of CA 125 in the tall columnar cells of the endocervical epithelium but not in the ectocervical squamous epithelium. We measured very high levels of CA 125 in liquefied cervical mucus from women with regular menstrual cycles. At midcycle, levels ranged from 14,200 to 153,000 U/ml (n = 13) in cervical mucus, while normal levels less than 35 U/ml were found in the corresponding serum samples. Levels of CA 125 in cervical mucus are comparable to the high levels found in cyst fluids from ovarian tumors (median 24,600 U/ml, n = 25). When secretion of cervical mucus was stimulated by ethinyl estradiol, equally high levels were found (7900 to 138,000 U/ml, n = 10). We conclude that the tumor marker CA 125 is synthesized and secreted by normal endocervical cells. Apparently an effective barrier exists between the endocervical mucosa and the circulation.