Concordance between CA-125 and RECIST progression (PD) in patients with germline BRCA-mutated platinum-sensitive, relapsed ovarian cancer treated with a PARP inhibitor (PARPi) as maintenance therapy after response to chemotherapy.

Abstract

6014 Background: There are no data to support CA-125 as a surrogate biomarker for ovarian cancer PD in patients on maintenance therapy with a PARPi. We aimed to assess the concordance of PD by CA-125 with RECIST PD in patients treated with maintenance PARPi. Methods: We extracted data on PD as defined by GCIG CA-125 and investigator-assessed RECIST from the SOLO2/ENGOT-Ov21 (NCT01874353) trial. Patients were categorized into: (i) CA-125 and RECIST non-PD concordant; (ii) CA-125 and RECIST PD concordant; and (iii) CA-125 and RECIST discordant. We excluded those with PD other than by RECIST, PD on date of randomization, and no repeat CA-125 beyond baseline. To assess the concordance of CA-125 PD with RECIST PD and CA-125 non-PD with RECIST non-PD, we computed the positive predictive value (PPV), i.e. the probability that patients with CA-125 PD also had RECIST PD, and negative predictive value (NPV), i.e. probability that patients with no CA-125 PD also did not have RECIST PD, respectively. Results: Of 295 randomised patients, 275 (184 olaparib, 91 placebo) were included in the primary analysis. 80 (29%) had CA-125 PD and 77 had concordant RECIST PD, resulting in a PPV of 96% (95% CI 90%-99%). Of 195 patients without CA-125 PD, 101 also did not have RECIST PD, resulting in a NPV of 52% (95% CI 45%-59%; Table). Among those with RECIST PD (n = 171), a greater proportion of patients with RECIST-only PD had a normal baseline CA-125 than those with both CA-125 and RECIST PD (94% vs 69%; p< 0.001). Of 94 patients without CA-125 PD but had RECIST PD, 65 (69%) had CA-125 that remained within normal range, while 27 (29%) had rising and elevated CA-125 that did not meet the criteria for GCIG CA125-PD. Discordance between RECIST PD and CA-125 non-PD was similar in early (≤12 weeks) and late ( > 12 weeks) PD (56% vs 55%, respectively; p= 0.96). Conclusions: Almost half the patients with RECIST PD did not have CA-125 PD and most had CA-125 still within the normal range. Regular imaging should be considered as part of surveillance in patients on maintenance olaparib rather than relying on CA-125 alone. [Table: see text]