Cancer antigen 125 is produced by human endometrial stromal cells*

Cancer antigen 125 (CA125) is an antigenic determinant defined by a murine monoclonal antibody and is present on the surface of some ovarian tumours. Using an immunoradiometric assay CA125 immunoreactivity was found in amniotic fluid and decidual extracts, hence the possibility of an endometrial origin of CA125 in pregnant and non-pregnant women was investigated. First-trimester decidual explants produced CA125 in vitro and cycloheximide significantly reduced the concentration of CA125 both in the medium and in the tissue. CA125 was also produced in primary culture of human endometrial stromal cells, its concentration in the medium being significantly higher with cells obtained during the proliferative and early secretory phases compared to those obtained during the late secretory phases. Medroxyprogesterone acetate (MPA, 1 mumol/l) induced a significant inhibition of CA125 production. This effect could be blocked by oestradiol (E2, 36 nmol/l) or the antiprogesterone RU486 (10 mumol/l). In women with endometriosis, the circulating levels of CA125 increased with the severity of the disease and were found to be significantly higher when compared to those of healthy volunteers. Gonadotrophin-releasing hormone or Danatrol therapy significantly reduced the CA125 levels. The endometrium, decidualized or not, seem to be capable of producing CA125, and this production is evidently correlated with endometrial cell growth and/or activity.