BARCELONA – There was no overall survival advantage for patients with metastatic colorectal cancer treated with the immune checkpoint inhibitor atezolizumab (Tencentriq) either in combination with cobimetinib (Cotellic) or as monotherapy compared with regorafenib (Stivarga), results of the randomized phase 3 IMblaze370 trial showed.
Median overall survival (OS, the primary endpoint) for 183 patients treated with atezolizumab and cobimetinib was 8.9 months, compared with 7.1 months for 90 patients treated with atezolizumab monotherapy, and 8.5 months for 90 patients treated with regorafenib. None of the differences were statistically significant, reported Johanna C. Bendell, MD, of the Sarah Cannon Research Institute in Nashville, Tenn.
“The lack of clinical activity may be due to the immune-excluded phenotype of metastatic colorectal cancer. The dual inhibition of the PD-L1 immune checkpoint and MAP kinase–mediated immune suppression may not be sufficient to generate that immune response that we need for antitumor activity,” she said at the European Society for Medical Oncology World Congress on Gastrointestinal Cancer.
In an interview, Dr. Bendell said that “we were all hoping that we were going to see some benefit, and we had some preliminary data suggesting that we would. What we still need to see is whether there are potentially populations of patients who might have benefited more, which hopefully will come out of the biomarker analysis.”
The results demonstrate the need for controlled comparison trials to detect true clinical benefits from a specific agent or combination, she added.
Microsatellite-stable disease, which accounts for approximately 95% of cases of metastatic colorectal cancer (MSS mCRC) is considered to be an immune-excluded or “cold” tumor type due to a lack of tumor-infiltrating lymphocytes. Single agent inhibitors of the programmed death 1 protein and its ligand (PD1/PD-L1) have only minimal activity in MSS mCRC, she noted.
In preclinical studies, there was evidence to suggest that the combination of atezolizumab and cobimetinib could augment antitumor T-cell responses. The combination also was shown to be safe and to demonstrate “promising” clinical activity in aconducted by Dr. Bendell and her colleagues.
To see whether the initial promise of atezolizumab in this population held up under closer scrutiny, the investigators enrolled patients with MSS mCRC refractory to chemotherapy and randomly assigned them on a 2:1:1 basis to receive either atezolizumab plus cobimetinib, atezolizumab monotherapy, or regorafenib.
Atezolizumab was administered intravenously at 840 mg every 2 weeks in the combination arm, and at 1,200 mg every 3 weeks in the monotherapy arm. Cobimetinib was administered orally at 60 mg on a 21-days-on/7-days-off schedule. Regorafenib was administered orally at 160 mg on a 21-days-on/7-days-off schedule.
As noted, the trial did not meet its primary endpoint of an OS benefit in the intention-to-treat population. In addition, there were no significant differences in either median progression-free survival, overall response rates, or duration of response.
Response rates for both the atezolizumab/cobimetinib combination and atezolizumab monotherapy arms were consistent with published data for other PD-1/PD-L1 inhibitors, and the safety of the combination was consistent with the known safety profiles of the individual agents, Dr. Bendell said.
The investigators are conducting extensive biomarker evaluations and gene expression profiles, and hope to present the results of these studies at a future conference, she added.
SOURCE: Bendell J et al. ESMO GI 2018. Abstract LBA-004.