Trial results for the investigation of atezolizumab with or without abemaciclib for metastatic castration-resistant prostate cancer (mCRPC) were posted on ClinicalTrials.gov on 2025-10-02. The study found that abemaciclib monotherapy in biomarker-unselected patients achieved a 100% 6-month Progression Free Survival (PFS) rate, while the combination of abemaciclib + atezolizumab showed an Objective Response Rate (ORR) of 12.5% in the biomarker-unselected randomized arm.
Background
This trial aimed to test the effectiveness and safety of abemaciclib, a molecularly targeted chemotherapy drug, and atezolizumab, an immunotherapy drug, both alone and in combination, for shrinking or preventing the growth of metastatic castration-resistant prostate cancer (mCRPC).
Trial design
The study (NCT04751929) was a Phase 2 trial with an enrollment of 19 participants. It investigated treatments for patients with Prostate Cancer and Metastatic Castration-resistant Prostate Cancer. The interventions included abemaciclib and atezolizumab. The trial design included several arms: Biomarker-Unselected Abemaciclib Monotherapy (Randomized), Biomarker-Unselected Abemaciclib + Atezolizumab (Randomized), CDK12 Mutation Atezolizumab Monotherapy (Non-Randomized), and CDK12 Mutation Abemaciclib + Atezolizumab (Non-Randomized).
Key results
Key outcome measurements from the trial include:
- 6-month Progression Free Survival (PFS) Rate:
- For the Biomarker-Unselected Abemaciclib Monotherapy (Randomized) group, the rate was 100% of participants.
- For the CDK12 Mutation Atezolizumab Monotherapy (Non-Randomized) group, the rate was 50% of participants.
- The rate for Biomarker-Unselected Abemaciclib + Atezolizumab (Randomized) was reported as NA.
- Objective Response Rate (ORR):
- For the Biomarker-Unselected Abemaciclib Monotherapy (Randomized) group, the ORR was 0% of participants (90% Confidence Interval).
- For the Biomarker-Unselected Abemaciclib + Atezolizumab (Randomized) group, the ORR was 12.5% of participants (90% Confidence Interval).
- For the CDK12 Mutation Atezolizumab Monotherapy (Non-Randomized) group, the ORR was 0% of participants (90% Confidence Interval).
- Number of Participants Experiencing Dose Limiting Toxicity (DLT):
- In the Biomarker-Unselected Abemaciclib Monotherapy (Randomized) group, 0 participants experienced DLT.
- In the Biomarker-Unselected Abemaciclib + Atezolizumab (Randomized) group, 4 participants experienced DLT.
- In the CDK12 Mutation Atezolizumab Monotherapy (Non-Randomized) group, 0 participants experienced DLT.
- In the CDK12 Mutation Abemaciclib + Atezolizumab (Non-Randomized) group, 0 participants experienced DLT.
- 12-month Overall Survival (OS):
- For the Biomarker-Unselected Abemaciclib Monotherapy (Randomized) group, OS was 83% of patients (90% Confidence Interval).
- For the Biomarker-Unselected Abemaciclib + Atezolizumab (Randomized) group, OS was 50% of patients (90% Confidence Interval).
What this means
The results from this Phase 2 trial provide initial insights into the efficacy and safety of abemaciclib and atezolizumab in mCRPC. The 100% 6-month PFS rate observed with abemaciclib monotherapy in biomarker-unselected patients is a notable finding, though this is from a small patient cohort. The combination of abemaciclib + atezolizumab demonstrated an ORR of 12.5% in a similar group, suggesting some activity. However, the combination also led to 4 participants experiencing Dose Limiting Toxicity (DLT) in the biomarker-unselected randomized arm, compared to 0 in the monotherapy arms. The 12-month OS data also shows variability between the monotherapy and combination arms. These early-phase results warrant further investigation in larger studies to confirm efficacy and better characterize the safety profile.
Source
The information regarding these trial results was obtained from ClinicalTrials.gov, a public database of clinical studies. The results for study NCT04751929, titled "Abemaciclib With or Without Atezolizumab for mCRPC," were posted on 2025-10-02 on clinicaltrials.gov.