I’m going to present data on the immune checkpoint inhibitor atezolizumab in patients with metastatic triple negative breast cancer. We treated 115 patients with atezolizumab; these are all patients with metastatic disease, most of them had at least one or two prior lines of treatment for metastatic disease, a small group of those patients also had no prior treatment for metastatic breast cancer.

What was your method and what did you find?

It was the expansion phase of a phase I study establishing the optimal dose of atezolizumab. We had 115 patients all with measurable disease, some appreciative, some not. Patients were initially selected by positive PD-L1 expression but later on we also allowed patients with low or negative PD-L1 expression in the study to get a better feel for PD-L1 as a biomarker in terms of response to single agent atezolizumab.
We had three really important findings in this study we are presenting today. The first finding is that atezolizumab works very well as single agent therapy but the best responses are seen in patients who receive the treatment as first line and first line triple negative breast cancer response rate was 26% whereas in later lines the response rate was just under 10%. The second important finding is that if patients respond to atezolizumab they have a very long duration of response with 21.1 months on average which, if you compare this to the median survival of patients with metastatic triple negative breast cancer which is between 9-12 months, this is a very significant result. The third important finding is the survival data of patients treated on this study. The median overall survival in this study was, unfortunately as expected, around 9 months but the survival of patients responding to atezolizumab was 100% of these patients were alive after one year, 100% of the patients were alive after two years which is a significant result and very different to what we normally see with chemotherapy in triple negative breast cancer.

Were there any adverse effects?

The treatment is generally well tolerated. What we saw in this breast cancer cohort is very much in keeping with what we know from immune checkpoint inhibitors in other diseases. About 10-11% of patients had grade 3/4 toxicity which, again if you put this in context with what we normally see with chemotherapy, is a very well tolerated treatment.

What could be the future implications of these findings?

The first implication is that we know if patients respond to immune checkpoint inhibitor therapy they have a substantial benefit with a long duration of response and probably a significant prolongation of survival. The downside at the moment is it’s a relatively small percentage of patients who benefit from single agent immune checkpoint inhibitor therapy so our efforts are now focussing on, first of all, better characterising the patients who do respond but, secondly, also to find better treatments, better combinations, that more patients will benefit from this. One of those conclusions is already to combine immune therapy with chemotherapy; there are large randomised phase III trials ongoing that explore the combination of chemotherapy with immune checkpoint inhibitors, including atezolizumab in metastatic triple negative breast cancer. We will hopefully see this treatment has a benefit over chemotherapy alone and that more patients will benefit compared to single agent immune checkpoint inhibitor therapy.