Follow-up with CA125 after primary therapy of advanced ovarian cancer has major implications for treatment outcome and trial performances and should not be routinely performed.

Background: Only one randomized trial has examined the value of performing routine CA125 measurements during follow-up of ovarian cancer. The results of this trial and implications of frequent CA125 measurements are examined.
Patients and Methods: The Medical Research Council OV05/European Organisation for Research and Treatment of Cancer 55955 trial enrolled 1442 patients with a CA125 level within the normal range following platinum-based chemotherapy for epithelial ovarian cancer. If CA125 levels rose to more than twice the upper limit of normal, patients were randomized to immediate or delayed chemotherapy.
Results: Those randomized in the early arm started chemotherapy a median of 4.8 months earlier than those on the delayed arm. There was no difference in survival between the early and delayed arms.
Conclusions: Women should be advised not to have routine CA125 measurements, providing they are well and have no symptoms suggesting relapse. In asymptomatic patients with a rising CA125 level, chemotherapy can be delayed. Earlier stopping of maintenance therapy just because of rising CA125 might deny patients continuing benefit from that therapy. Use of CA125 to define progression could result in platinum-sensitive patients being falsely classified as platinum resistant.