Defining response of ovarian carcinoma to initial chemotherapy according to serum CA 125

To produce definitions based on serial CA 125 levels to measure response of ovarian carcinoma in patients receiving first-line chemotherapy.

Definitions were derived from analysis of 277 patients in North Thames Ovary Trial 3. Patient data were then incorporated into a computer program and tested against 254 patients in North Thames Ovary Trial 4 and 458 patients in Gynecologic Oncology Group (GOG) protocol 97. For optimum detection of response, three response definitions have been combined into a computer program. The precise definitions use mathematic logic and take account of factors such as intervening samples. Response to a specific treatment has occurred if after two samples there has been a 50% decrease, confirmed by a fourth sample (50% response), or a serial decrease over three samples of greater than 75% (75% response). The final sample has to be at least 28 days after the previous sample.

Six hundred twenty of 989 patients were considered assessable for response according to CA 125 level. Only two patients (0.3%) had a CA 125 response at the time of clinical progression. The CA 125 response rate was 62% and 54% in the North Thames trials. In the GOG trial, it was 66% in all 317 patients assessable for CA 125 and 67% in 221 patients whose CA 125 level was not measurable according to GOG criteria, compared with a GOG-defined response rate of 62%. The sensitivity for detecting GOG-defined response was at least 68%.

Definitions based on a 50% or 75% decrease of CA 125 levels have been shown reliably to define partial response of ovarian cancer in patients receiving first-line chemotherapy. These definitions should be used in addition to or instead of standard response criteria.