a blood test used to determine the presence of CA 125 serum tumor marker, which has a high degree of sensitivity and specificity for ovarian cancer. It is a useful tumor marker for evaluating therapy and monitoring disease status in patients under treatment for ovarian cancer. CA-125 is a mucin like glycoprotein. It is a surface antigen associated with nonmucinous epithelial ovarian cancer. The protein is sloughed or secreted from the surface of the ovarian cancer cells into the serum or ascites also made by inflamed normal cells that line body parts. This substance is shed in body fluids and finds its way into the bloodstream.