Are CASA and CA125 concentrations in peripheral blood sourced from peritoneal fluid in women with pelvic masses?

Background. The Cancer associated serum antigen (CASA) and CA125 assays used in the management of ovarian cancer measure distinct high molecular weight glycoproteins. The mechanisms of secretion of these molecules into the peripheral circulation are not clearly understood. Methods. Concentrations of CASA and CA125 were assessed in peripheral blood, blood from veins draining ovarian and omental tumors, and peritoneal fluid in 20 women with pelvic masses. Results. There was a near perfect correlation between peripheral vein and ovarian vein concentrations for both markers; concentrations in omental veins were higher than in peripheral veins in only a small proportion of cases, whereas the concentration in peritoneal fluid was universally much higher than in blood. Conclusions. These studies suggest a similar route of entry into the peripheral circulation and a similar half‐life for these glycoproteins. These data provide no support for the hypothesis that a significant contribution to CA125 concentrations comes from peritoneal release by mesothelial cells rather than tumor cells, because the relative CA125 concentrations between compartments were similar to those of CASA within patients. The lack of a gradient between CASA levels in peripheral blood and tumor draining veins suggests that the CASA half‐life is much longer than that predicted in animal studies. CA125 and CASA in peripheral blood are probably derived from markers secreted into peritoneal fluid and lymph, rather than directly into the bloodstream.