The preliminary results are quite compelling. First, looking at patient characteristics, the majority of patients who were on the study had prior therapy in the adjuvant setting. About 63% or so had either neoadjuvant or adjuvant therapy. About half of the patients on the study had previously seen taxane-based therapy, and about 90% of the patients on the trial were being treated in the first-line metastatic setting.
It is worth noting that about 7% of patients had node-only disease. Eligibility criteria allowed for any PD-L1 [programmed death-ligand 1] status. Biopsies were collected to check PD-L1 status using the SP142 assay. When they analyzed PD-L1 status on the submitted tumors, about 41% of patients had PD-L1 positivity based on the criteria used in the study. The preliminary results from the first report of over year ago were quite compelling.
Progression-free survival in the intention-to-treat population met statistical significance and reflected about 20% improvement, with an increase of around 18% to 24%, at 1-year median progression-free survival. In the PD-L1–positive subset of patients, this is where we really started to see the greatest impact. The improvement in progression-free survival with the addition of atezolizumab was approximately 40%. Therefore, the statistical plan allowed us to look at the overall survival data.
In the intention-to-treat population, for overall survival, there was a modest difference. Where there was great enthusiasm was in the exploratory look at the PD-L1–positive patients. That particular group had an absolute difference measured, in the updated data, of about 7 months in median overall survival. There was not a statistical analysis of this. This was an exploratory look, but it was quite compelling for PD-L1–positive patients with triple-negative breast cancer regarding the addition of atezolizumab to nab-paclitaxel.
These data, when they were presented, were quite practice changing. They led to the FDA approval of atezolizumab in addition to nab-paclitaxel for patients with PD-L1–positive, metastatic triple-negative breast cancer. I think it has been adopted widely in practice, where it is quite important to understand the PD-L1 status of patients with triple-negative breast cancer to be able to select appropriate therapy for them. It is important to note the assay used in IMpassion130 was the VENTANA PD-L1 SP142 assay. The definition of PD-L1 positivity was 1% or greater staining in the immune cells. Keep that in mind as you are thinking about PD-L1 testing in your patients with metastatic triple-negative breast cancer.
A question that remains is what we are to do when our patients experience progression of disease on a checkpoint inhibitor. I think at this point we really do not have data to support continuation of checkpoint blockade. This study can’t answer the question of what to do upon progression of disease. It is a robust area for clinical trials right now, and I would encourage you to look in your community for studies that are exploring combination therapies or checkpoint inhibitors upon progression on a checkpoint inhibitor.
Transcript Edited for Clarity
Barbara Jacoby is an award winning blogger that has contributed her writings to multiple online publications that have touched readers worldwide.