Men with metastatic castration-resistant prostate cancer (mCRPC) that had progressed despite treatment with novel hormonal therapy had a slight but statistically significant improvement in progression-free survival (PFS) with a combination of a targeted agent and immunotherapy compared with a second-line novel hormonal therapy.
The combination of the tyrosine kinase inhibitor (TKI), cabozantinib (Cabometyx), and the immune checkpoint inhibitor (ICI), atezolizumab (Tecentriq), was associated with a median PFS of 6.3 months vs 4.2 months for patients assigned to second hormonal therapy with either abiraterone (Zytiga) and prednisone, or enzalutamide (Xtandi) in the CONTACT-02 trial, Neeraj Agarwal, MD, reported at the ASCO Genitourinary Cancers Symposium.
"CONTACT 2 is the first phase 3 trial of the TKI/ICI combination to show statistically significant improvement in PFS in patients with mCRPC," said Dr Agarwal, of the Huntsman Cancer Institute at the University of Utah in Salt Lake City.
The data support the combination of cabozantinib and atezolizumab as a potential new treatment option for patients with mCRPC that has progressed on novel hormonal therapy, he said.
Study Design Questioned
That opinion, however, was not shared by Kim N. Chi, MD, of the University of British Columbia in Vancouver, BC, Canada, the invited discussant.
Dr Chi acknowledged that the study results as presented were positive, but also pointed to several limitations, including the small difference between the treatment groups in radiographic progression-free survival (rPFS).
"I would say the rPFS benefit is modest, and in the absence of other improvements, the difference in the median rPFS is equivalent from one scan to the next in the scanning cycle. I would argue about the clinical significance of that," he said.
He also noted that there was no improvement in the investigational arm in patient-reported outcomes, and that pain progression and quality-of-life deterioration occurred within 2-4 months, which is "quite quick."
Additionally, he questioned the choice of an androgen receptor pathway inhibitor (ARPI) switch as the control arm of the study.
"I'd also argue that ARPI switch is not the best standard of care for this patient population with measurable disease and 40% visceral metastases; there are better options," he said.
For example, in phase 3 trials, docetaxel and cabazitaxel (Jevtana) have consistently demonstrated radiographic PFS of 8-9 months. In addition, lutetium-177–PSMA-617, a radioligand therapy that delivers beta-particle radiation to PSMA-expressing cells and the tumor microenvironment, has also been shown to have PFS and overall survival benefits, he said.
"Irrespective of regulatory decisions, I personally could not recommend this at this time, given the data that we've seen and the better options that are available for this patient population," Dr Chi said.
Real-World Practice
"Kim Chi offered a pretty fair critique and summary of the control arm, but in real-world practice, ARPI switch, from abi [abiraterone] to enza [enzalutamide] or enza to abi continues to be used in routine clinical practice for various reasons," Xin Gao, MD, a genitourinary oncologist at Mass General Cancer Center in Boston, said in an interview.
"There are patients who can't tolerate chemotherapy or don't want chemotherapy, and we do know also that there are patients who can benefit from an ARPI switch, especially some patients with more indolent disease," said Dr Gao, who attended the presentation but was not involved in the study.
He noted that some patients being switched from abiraterone to enzalutamide have clinical responses, and that the ARPIs are generally more tolerable than chemotherapy.
In addition, CONTACT-02 is one of a series of trials in which ARPI switch was used as the control arm, and many of these trials were initiated before there were data confirming the superior efficacy of some newer therapeutic options, Dr Gao noted.
He agreed, however, that there is growing evidence to show that ARPI switch may not be the optimal choice for patients with more measurable disease, especially visceral metastases, and other more aggressive forms of mCRPC.
CONTACT-02 Details
Investigators in the phase 3 study screened 866 men with mCRPC and after stratification by liver metastases, prior docetaxel use for castration-sensitive prostate cancer, and disease stage for which the first novel hormonal therapy was given. About 500 patients (507) were randomized to receive either oral cabozantinib 40 mg daily plus intravenous atezolizumab 1200 mg every 3 weeks or second hormonal therapy with either abiraterone 1000 mg with oral prednisone 5 mg twice daily or oral enzalutamide 160 mg daily.
After a median follow-up of 14.3 months in the PFS intention-to-treat population, the median PFS by blinded central review was 6.3 months with cabozantinib/atezolizumab and 4.2 months with second hormonal therapy. This translated into a hazard ratio of 0.64 (P = .0002). The results were similar for a PFS analysis according to Prostate Cancer Working Group 3 criteria.
The combination was also associated with modest improvements in PFS in prespecified subgroups, including patients who had liver or bone metastases and those who had previously received docetaxel.
There were no significant differences in overall survival at the time of data cutoff. Overall survival data were not mature and will be reported at a later date.
Disease control rates, a composite of complete and partial responses and stable disease, were 73% with the combination and 55% with second hormonal therapy (P value not shown).
Safety Data
The safety analysis indicated that patients found the ARPI switch easier to tolerate than the combination.
Adverse events leading to dose reductions occurred in 40% of patients on the combination, vs 3% of patients on second hormonal therapy, and treatment-related adverse events leading to discontinuation occurred in 13% and 2%, respectively.
Grade 3 or 4 adverse events occurred in 48% of patients assigned to the combination vs 23% of patients assigned to the ARPI switch.
In all, 8% of patients on the combination and 12% on second hormonal therapy died on study, but none of the deaths were deemed to be treatment related.
CONTACT-02 was sponsored by Exelixis in partnerships with Ipsen and Takeda.
Dr Agarwal disclosed institutional research funding from Exelixis, Roche, Takeda, and others and travel expenses from Pfizer. Dr Chi disclosed honoraria, a consulting/advisory role and institutional research funding, with Roche and others. Dr Gao has served as a consultant or advisor to several companies, not including the sponsors of the study, and has served as principal investigator at his institution, which has received research funding from Exelixis, Takeda, and others.
This article originally appeared on MDedge.com, part of the Medscape Professional Network.
Â