KEYNOTE-046 (Part B): Effects of ADXS-PSA in combination with pembrolizumab on survival in metastatic, castration-resistant prostate cancer patients with or without prior exposure to docetaxel.

Abstract

126 Background: ADXS-PSA, an attenuated Listeria monocytogenes-based immunotherapy targeting prostate-specific antigen (PSA), is currently being evaluated in combination with pembrolizumab as a treatment for progressive metastatic castration-resistant prostate cancer (mCRPC) in the phase 1/2 KEYNOTE-046 trial (Part B). Methods: A total of 37 patients received 1x109 CFU + 200 mg pembro IV every 3 wks, for up to 2 yrs or until progression/toxicity. Results: At entry, patients were ~70 yrs with median a Gleason score of 9, and bone predominant disease (70%). MSI-High was negative in 36 pts who were able to be tested. Eighteen (48.6%) patients had received prior docetaxel, 15 pts of whom (83.3%) had also received 1-2 next generation hormonal agents (NGHAs). Nineteen (51.3%) had not received prior docetaxel and 16 of these pts (84.2%) had received 1-2 NGHAs. Overall, 16 out of 37 pts (43%) had a decreased PSA post-BL with 6/37 (16%) pts achieving a confirmed PSA reduction ≥50% from baseline. The median OS (months) for the whole group (37 pts) was 33.6 m (95% CI, range 15.4-33.6 months). The mOS for pts with and without prior exposure to docetaxel was 16 m (5.9 -33.6) and NR at 30 months of follow-up (15.4-NR), respectively. Prolonged survival was observed in pts regardless of prior therapies, microsatellite stable (MSS) status or PSA delta <50% or ≥50%. Conclusions: Results with ADXS-PSA in combination with pembrolizumab in mCRPC, with or without prior docetaxel, show promising clinical activity to be further assessed in randomized studies. Clinical trial information: NCT02325557.