LBA5002 Background: Abagovomab, a murine monoclonal anti-idiotypic antibody directed against CA125, has been shown to induce an active immune response against CA125 tumor-associated antigen in advanced ovarian cancer patients. Methods: Abagovomab (A) has been tested in a randomized (2:1) double-blind, placebo (P) controlled, multicenter phase II/III trial in patients with FIGO stage III/IV ovarian cancer after complete response to platinum-taxane first-line chemotherapy. A (2 mg/1 ml) or P was given subcutaneously every 2 weeks for 6 weeks (induction phase); then every 4 weeks (maintenance phase) until recurrence, or up to 21 months after the last patient had been randomized. Primary endpoint is progression-free survival (PFS); secondary endpoints are OS and immunological response. An estimated 870 patients, with a mean follow-up of 18 months, were needed to observe at least 535 recurrences, which provides a power >90% in rejecting the null hypothesis of equality between A and P on PFS according to a hazard ratio (HR) of 1.33, in which median P PFS time is 18 months, significance level (a) 5% (two-sided), and the overall dropout rate 10%. Primary analysis was run on PFS in the ITT population. The design included a prospective stratification in randomization for the following prognostic factors: FIGO stage (III-IV); tumor size after debulking (residual tumor <1 cm, >1 cm); and CA125 serum level after the third cycle (<35 U/ml, >35 U/ml). The Cox proportional hazards model was used for adjusting the primary analysis. Results: 888 patients were enrolled by December 2008, 593 in A arm and 295 in P arm. The median follow-up was 28.1 months and the mean number treatment administrations was 18. Baseline characteristics were balanced between arms. Overall tolerability profile was consistent with previous A studies. Median (95% CI) PFS was 13.24 (10.612-13.602) months for A arm and 13.21 (10.612-16.000) months for P arm; HR=1.099 (0.919-1.315); p=0.301. Conclusions: Treatment with A did not translate into a prolonged PFS.
