Final survival follow-up and translational associations using interval indirect immunization with oregovomab (O) and poly ICLC in patients (pts) with recurrent platinum-resistant ovarian cancer (PROC).

Abstract

e17545 Background: Indirect immunization with tumor specific antibody is an approach to triggering therapeutic immunity to cancer through activated immune cells. O is a monoclonal IgG1 specific to CA125 (MUC16). O is currently in phase III evaluation of front-line chemoimmunotherapy (CIT), having shown benefit relative to chemotherapy alone in a randomized phase II study (Brewer, Gyn Onc 2020). H is a TLR3 agonist used as a stimulatory immune adjuvant. The dosing phase of the protocol established safety and compatibility of this combination. The primary safety and response outcomes were reported at IGCS-2019. Immune parameters and long-term outcome associations are the focus of this final update. Methods: Pts with heavily treated RECIST evaluable platinum resistant ovarian cancer (median of 5 prior Rx) received 4 IV infusions with 2 mg O followed by 2mg H IM 30 min & 48 hrs post O at wks 0, 3, 6, 9. At wk 12 imaging was performed and elective salvage Rx allowed. A fifth O+H was optional at wk 16. Study endpoints included immune associations after O+H, after second-line chemotherapy, and survival outcomes. Results: 17 pts were enrolled at 2 centers; 15 patients were dosed and 13 completed the specified minimum 3 infusions. The treatment was well tolerated with local reactions and mild flu like symptoms (13/15 pts) as the only reported adverse events. There was no treatment related serious adverse events. Median survival was 15.0 m [95% CI:10.8m-NE] and 4 patients remained alive at data lock (median 26.5 m). H stimulated an early humoral antibody response to O at wk 6 in 7 of 9 pts (78%). Interval administration of second-line Rx (bevacizumab, paclitaxel, carboplatin, &/or doxorubicin) and O were associated with further antibody spikes. Baseline neutrophil monocyte to lymphocyte ratio (NMLR), a measure of myeloid-derived immune suppression was inversely associated with survival. PROC patients with baseline NMLR ≤4x (n = 8) had median OS 19.6m [15.0 m -NE] vs median OS 10.8m [3.6m-NE] HR 2.44 [0.73-8.15], ( p= 0.13) for pts with NMLR > 4.0 (n = 7). Conclusions: H is a viable immune adjuvant for combination with O suitable for further study in immune resistant settings. Immune responsiveness was similar to that observed in a prior study of same day schedule of carboplatin-paclitaxel front-line immunotherapy (Braly, JIT 2009; Battaglia, Cll, 2020). Patterns of immune response to O in the setting of recurrent ovarian cancer are influenced by concomitant anti-neoplastic therapy. Clinical outcomes appear sensitive to myeloid burden (NMLR > 4) which may be more prevalent in patients with treatment resistant disease than in chemotherapy naïve patients, as previously observed in front-line CIT trials. A phase III study to further evaluate these associations in the front-line setting is currently underway NCT04498117. Clinical trial information: NCT03162562.