Elevated serum CA 125 levels in patients with benign ascitic or pleural effusions.

The tumor-associated antigen CA 125 is widely used in monitoring of ovarian carcinomas. As this determinant is also expressed in proliferating mesothelia, we studied CA 125 levels in serum and effusion fluid of patients with ascitic and pleural effusions. Patients with benign and malignant disease were included. There was no statistically significant or diagnostically useful difference between 26 benign and 44 malignant cases in the CA 125 levels in effusions or sera. In 77% of benign cases, serum levels exceeding 105 U/ml (3 times the recommended upper limit of normal values) were found. Thus, in patients with serous effusions, elevated serum CA 125 values alone do not provide evidence for the presence of an (ovarian) malignancy, but may also indicate a proliferation of mesothelium due to benign disease.