Background: There is a need to delineate how the best available serum marker for ovarian cancer, CA 125 should be used in monitoring the treatment of individual patients, and in clinical trials.
Patients and methods: The situations where measurement of CA 125 could alter the management of individual patients during therapy and at relapse were critically analysed. Precise definitions for response according to CA 125 were first developed and tested on 989 patients receiving first line therapy and have since been tested on over 2000 patients in phase 2 trials. Precise definitions for progression were developed from 71 patients during and on 255 patients both during and after initial chemotherapy.
Results: In individual patient management, progression on initial chemotherapy can be demonstrated by serial rise in CA 125 suggesting the need for a change in therapy. A confirmed doubling of CA 125 from the upper limit of normal during follow up accurately predicts relapse. This endpoint needs prospective testing for use in clinical trials. Precise definitions of response based on a 50% or 75% fall in CA 125 levels accurately predicts whether a cytotoxic agent is active against ovarian cancer.
Conclusion: Precise definitions of response based on CA 125 should be used in phase 2 trials of new cytotoxic drugs.