In a phase III clinical trial of people with previously untreated metastatic renal cell cancer (mRCC), combining immunotherapy atezolizumab with targeted therapy bevacizumab delayed cancer growth by about three months longer than sunitinib, another targeted therapy. The benefit of atezolizumab plus bevacizumab was greater for patients with PD-L1-positive tumors. These findings were presented at ASCO's 2018 Genitourinary Cancers Symposium in San Francisco, California.

"The side effects of atezolizumab plus bevacizumab were decidedly less harsh than sunitinib. And because progression-free survival was also better, I am confident that this relatively easy-to-administer combination will be a strong treatment choice in all medical practices," said lead study author Robert J. Motzer, MD, a medical oncologist at Memorial Sloan Kettering Cancer Center, New York.

Renal cell cancer is the most common type of kidney cancer in adults. IMmotion151 is the first randomized, phase III combined immunotherapy with bevacizumab trial in people with untreated mRCC. Starting in 2015, sites worldwide enrolled 915 adults who were randomly assigned to receive either atezolizumab plus bevacizumab intravenously every 3 weeks or take a sunitinib pill daily for 4 weeks followed by two weeks off treatment.

Atezolizumab is an immune checkpoint inhibitor that blocks the PD-L1 protein on the surface of tumor cells, allowing the immune system to recognize and attack those cells. Bevacizumab and sunitinib are targeted medicines that block the growth of blood vessels to the tumor, thereby limiting its growth. 

"With the introduction of checkpoint inhibitors, clinicians started looking at combinations of these medicines with anti-angiogenic medicines like bevacizumab," said Dr. Motzer. "Bevacizumab may affect the local immune response in the tumor and help prime the response of tumor and immune cells to immune-system activators like atezolizumab."

For the analysis, the researchers grouped patients according to PD-L1 expression on immune cells in the tumor (so-called tumor infiltrating immune cells). Tumors that had the PD-L1 protein detected on the surface of at least 1% of those immune cells were considered PD-L1-positive, and all other tumors were considered PD-L1-negative.

The study had co-primary endpoints were investigator-assessed progression-free survival in the PD-L1-positive group and overall survival in the group of all enrollees (the intention-to-treat (ITT) population).

At a median follow-up of 15 months, patients in the PD-L1-positive group treated with atezolizumab and bevacizumab had a 26% lower chance of the cancer progressing than those who received sunitinib; the median time until the cancer progresssed was also 3.5 months longer (median 11.2 months in the atezolizumab plus bevacizumab group vs. 7.7 months in the sunitinib group).

In the ITT group, a benefit of atezolizumab plus bevacizumab was also observed, though more modest. Those treated with atezolizumab and bevacizumab had a 17% lower chance of cancer progressing, with a median time of 2.4 months longer until the cancer progressed. The difference in overall survival between the two treatment regimens was not statistically significant at this early interim analysis. Overall survival data are still immature, and the authors are planning an updated analysis as more data accrues.

Treatment-related side effects were less frequent in the atezolizumab and bevacizumab group, occurring in 40% of people, compared to 54% of people in the sunitinib group. Twelve percent of people in the atezolizumab and bevacizumab group, and 8% in the sunitinib group, stopped at least one treatment component due to treatment-related side effects during the trial.

"Adding immunotherapy to existing targeted therapies has shown promising results in recent clinical trials. We're pleased to see validation of this approach through this large trial in advanced kidney cancer, a disease that remains incurable for most patients," said ASCO Expert Sumanta K. Pal, MD.

"For an aggressive cancer like this, where less than 20% of people survive 5 years after diagnosis, we think a 3.5-month longer progression-free survival, given the tolerability for this new combination treatment regimen, is an important development," said Dr. Motzer.

The study will continue to assess overall survival as specified by protocol as well as secondary endpoints. In addition, the researchers collected tumor tissue and will look at molecular profiles to try to tease out markers, in addition to PD-L1, in the people who responded best to the combination therapy. Dr. Motzer said the researchers may look at novel therapies that could be added to atezolizumab so they could devise treatments to boost survival odds even higher.

This study was funded by F. Hoffmann-La Roche Ltd., Basel, Switzerland.