Very high CA 125 levels prior to surgery are associated with a worse prognosis. In women with stage I disease a pre-operative level >65 U/ml is a powerful adverse prognostic indicator, and such patients are candidates for chemotherapy rather than surveillance. Elevated CA 125 levels after one, two, or three courses of chemotherapy are important adverse prognostic factors for survival. Serial changes in CA 125 are recognized as one of the best methods for monitoring therapy.
A persistently elevated CA 125 after oophorectomy for suspected stage I disease is evidence of residual tumour.
A biological response based on CA 125 has been defined as either a 50% or a 75% reduction in CA 125 levels. To reduce the chance of falsely predicting a response, the 50% CA 125 response definition requires four CA 125 levels—two initial elevated samples, and the sample showing a 50% decrease requires confirmation by a fourth sample. The 75% CA 125 response definition requires only three CA 125 levels, with a serial decrease of at least 75%. In both 50% and 75% response definitions, the final sample has to be at least 28 days after the previous sample.
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