Trial results for a Phase 3 study (NCT04740918) investigating atezolizumab in combination with trastuzumab emtansine for participants with HER2-positive and PD-L1-positive locally advanced or metastatic breast cancer were posted on ClinicalTrials.gov on 2025-08-08. The combination arm showed a median duration of response (DOR) of 15.57 months, compared to 8.21 months for the placebo combination arm.
Background
This Phase 3 study investigated atezolizumab in combination with trastuzumab emtansine for participants with Human Epidermal Growth Factor 2 (HER2)-positive and Programmed Death-ligand 1 (PD-L1)-positive locally advanced (LABC) or metastatic breast cancer (MBC). Participants had previously progressed during or after trastuzumab- and taxane-based therapy for LABC/MBC, or within six months of completing such therapy in the neoadjuvant and/or adjuvant setting.
Trial design
The study (NCT04740918) was a Phase 3 trial that enrolled 96 participants with Metastatic Breast Cancer. Specifically, the study focused on participants with HER2-positive and PD-L1-positive locally advanced or metastatic breast cancer. Participants were randomized to receive either trastuzumab emtansine 3.6 mg plus atezolizumab 1200 mg or trastuzumab emtansine 3.6 mg plus placebo.
Key results
The trial evaluated outcomes for trastuzumab emtansine 3.6 mg plus atezolizumab 1200 mg compared to trastuzumab emtansine 3.6 mg plus placebo.
- For Progression-Free Survival (PFS), the median was 8.61 months for the atezolizumab combination arm versus 7.52 months for the placebo combination arm. The Hazard Ratio (HR) was 0.75 (95.0% Confidence Interval: 0.44 to 1.28), with a p-value of 0.2876.
- Objective Response Rate (ORR) was 53.3 percentage of participants for the atezolizumab combination arm, compared to 49 percentage of participants for placebo. The Odds Ratio (OR) was 1.16 (95.0% Confidence Interval: 0.5 to 2.7), with a p-value of 0.724.
- The median Duration of Response (DOR) was 15.57 months for the atezolizumab combination arm, versus 8.21 months for the placebo combination arm. The Hazard Ratio (HR) was 0.65 (95.0% Confidence Interval: 0.26 to 1.61), with a p-value of 0.3531.
- In participants with baseline brain metastases, median PFS was 4.78 months for the atezolizumab combination arm compared to 7.69 months for the placebo combination arm. The Hazard Ratio (HR) was 1.59 (95.0% Confidence Interval: 0.39 to 6.43), with a p-value of 0.5151.
- Overall Survival (OS) data was reported as NA for both treatment arms, including for participants with baseline brain metastases.
What this means
The results from this Phase 3 trial show that the addition of atezolizumab to trastuzumab emtansine led to a numerically longer median duration of response in participants with HER2-positive and PD-L1-positive locally advanced or metastatic breast cancer, reaching 15.57 months compared to 8.21 months with placebo. While the median progression-free survival was also numerically higher in the atezolizumab arm, the statistical analyses for these endpoints did not demonstrate statistical significance. Notably, in the subgroup of participants with baseline brain metastases, the atezolizumab combination arm showed a numerically shorter median PFS compared to the placebo combination arm. These findings provide data on the efficacy profile of this combination in a challenging patient population.
Source
The information regarding these trial results was obtained from ClinicalTrials.gov, a public database of clinical studies. The results for study NCT04740918, titled "A Study of Trastuzumab Emtansine in Combination With Atezolizumab or Placebo as a Treatment for Participants With Human Epidermal Growth Factor 2 (HER2)-Positive and Programmed Death-ligand 1 (PD-L1)-Positive Locally Advanced (LABC) or Metastatic Breast Cancer (MBC)," were posted on 2025-08-08 on clinicaltrials.gov.