Exelixis, Inc. (NASDAQ:EXEL) today announced encouraging results from the metastatic castration-resistant prostate cancer (CRPC) cohort of COSMIC-021, the phase 1b trial of cabozantinib (CABOMETYX®) in combination with atezolizumab (TECENTRIQ®) in patients with locally advanced or metastatic solid tumors. The data will be presented on Thursday, February 13th during Poster Session A: Prostate Cancer at 11:30 a.m. – 1:00 p.m. PT and 5:30 – 6:30 p.m. PT at the 2020 American Society of Clinical Oncology’s Genitourinary Cancers Symposium (ASCO GU 2020), which is being held in San Francisco, California, February 13 – 15, 2020.
Upon enrollment, patients had to have measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST v. 1.1) and had progressed on prior novel hormone therapy and could have received prior docetaxel for hormone sensitive disease. Forty-four patients were included in this interim analysis. The median follow up was 12.6 months. The objective response rate (ORR) per RECIST v. 1.1, the trial’s primary endpoint, was 32%, including two complete responses and 12 partial responses. Disease control rate was 80%. Among the 36 patients with high-risk clinical features including visceral metastases and/or extra-pelvic lymph node metastases, the ORR was 33%. Median duration of response for all responding patients was 8.3 months. Among 12 patients who had an objective response and at least one post-baseline prostate-specific antigen (PSA) evaluation, 67% had a PSA decline of at least 50%.
“Given the poor prognosis for men with metastatic castration-resistant prostate cancer, measurable visceral disease and/or extra-pelvic lymph node metastases who have progressed on novel hormone therapies, we are excited to observe clinically meaningful activity with the combination of cabozantinib and atezolizumab in this COSMIC-021 cohort,” said Neeraj Agarwal, M.D., Professor, Huntsman Cancer Center, University of Utah, and an investigator of the trial. “Emerging data suggests a tolerable safety profile and encouraging efficacy for this combination that may hold promise for these patients with limited treatment options, potentially providing patients with more time before the need for treatment with chemotherapy. We look forward to additional results as the trial progresses.”
The median treatment duration was 6.3 months (range 1 to 18 months). No new safety signals were identified in this combination cohort. Treatment-related grade 3/4 adverse events (AEs) occurring in =5% of patients were fatigue (7%), diarrhea (7%) and hyponatremia (7%). One treatment-related grade 5 AE of dehydration was reported in a 90-year-old patient. The discontinuation rate of study treatment for adverse events unrelated to disease progression was low at 7%.
Exelixis announced on January 7, 2020 that metastatic CRPC cohort 6 of COSMIC-021 had been expanded to enroll up to 130 patients. Based on regulatory feedback from the U.S. Food & Drug Administration (FDA), and if supported by the clinical data from the recently expanded existing cohort and added metastatic CRPC cohorts, Exelixis intends to file with the FDA for accelerated approval in a metastatic CRPC indication as early as 2021.
“We’re happy to share these encouraging results from the metastatic CRPC cohort from COSMIC-021, our first trial evaluating the combination of cabozantinib and atezolizumab,” said Gisela Schwab, M.D., President, Product Development and Medical Affairs and Chief Medical Officer, Exelixis. “We look forward to receiving data from the most recent expansion of this CRPC cohort while we are also preparing for the initiation of a phase 3 pivotal trial in this indication. We are excited about the emerging data in metastatic CRPC and elsewhere and the potential of combining cabozantinib with immunotherapies in this and other difficult-to-treat tumor types.”
More information about this trial is available at ClinicalTrials.gov.