CHICAGO – The antiangiogenic agent pazopanib is not efficacious when used as adjuvant therapy for resected renal cell carcinoma (RCC) with features that confer a high risk of recurrence, the PROTECT investigators reported at the annual meeting of the American Society of Clinical Oncology.
Pazopanib (Votrient) is an oral multitargeted tyrosine kinase inhibitor active against the vascular endothelial growth factor receptor (VEGFR). Adjuvant use of other agents in this class has yielded mixed results, noted lead investigator Robert J. Motzer, MD, of Memorial Sloan-Kettering Cancer Center in New York.
Dr. Robert J. Motzer
In PROTECT, a phase III randomized controlled trial of more than 1,500 patients who had undergone nephrectomy for high-risk locally advanced RCC, pazopanib started at 600 mg daily did not yield significantly better disease-free survival than placebo, the trial’s primary endpoint. The drug did have a significant benefit when started at 800 mg daily, but that dose had to be lowered partway through because of a high rate of discontinuation due to adverse events.
“The trial did not meet its primary endpoint,” Dr. Motzer concluded. “Pazopanib is not recommended for adjuvant therapy following resection of locally advanced RCC.”
Expert perspective
“The current landscape of RCC adjuvant therapy is really controversial,” commented invited discussant Daniel Y. C. Heng, MD, MPH, of the University of Calgary (Alta.) Tom Baker Cancer Centre.
Susan London/Frontline Medical News
Dr. Daniel Y. C. Heng
“Are these [factors] important or not? I think a lot of this is being overshadowed by things that are going on right now,” Dr. Heng maintained. “There are newer medications, such as PD-1 and PD-L1 inhibitors that are now being studied. And there are now perioperative studies as well – should we be using these drugs before nephrectomy and after nephrectomy to prime the immune system to get better outcomes?”
At the end of the day, identification of a reliable predictive biomarker will be key to using the VEGFR tyrosine kinase inhibitors, he concluded. “I look forward to the future where we can actually use these tests to determine who will benefit most from adjuvant therapy so that we can maximize patient outcomes.”
Study details
The PROTECT trial was funded by Novartis Oncology and randomized 1,538 patients with resected pT2 (high grade), pT3, or greater nonmetastatic clear cell RCC, a highly vascular tumor typically reliant on aberrant signaling in the VEGF pathway.
The patients were assigned evenly to receive pazopanib or placebo for 1 year. The starting dose was lowered from 800 mg daily to 600 mg daily (with escalation permitted) after 403 patients had been treated.
In intention-to-treat analysis among patients started on the 600-mg dose and having a median follow-up of about 31 months, disease-free survival was better with pazopanib but not significantly so (hazard ratio, 0.86; P = .16), Dr. Motzer reported.
In secondary analyses, pazopanib did have a significant disease-free survival benefit among patients started on the 800-mg dose (hazard ratio, 0.69; P = .02) and among the entire trial population started on either dose (hazard ratio, 0.80; P = .01).
One possible explanation for the differing results seen with the two doses was the difference in follow-up, as the 800-mg group was treated earlier in the trial, he proposed. But with an additional year of blinded follow-up, the benefit in the 600-mg group actually diminished, whereas that in the 800-mg group did not.
Another possibility was the somewhat better performance of the placebo group used for comparison with the lower dose: the 3-year disease-free survival rate with placebo was 64% for the 600-mg comparison but 56% for the 800-mg comparison. “One factor that could explain differences in the outcomes of the placebo groups includes unidentified patient demographic characteristics,” Dr. Motzer noted.
Overall survival was statistically indistinguishable between the pazopanib and placebo groups, regardless of dose. However, “the results are inconclusive as the data are not yet mature,” he said, with a definitive analysis planned for 2019.
Compared with counterparts given placebo, patients started on the 600-mg dose of pazopanib had a higher rate of grade 3 or 4 adverse events overall (60% vs. 21%), driven in large part by higher rates of hypertension and increased alanine aminotransferase levels.
“Although the intent of modifying the protocol dose of pazopanib from 800 mg to 600 mg was to reduce the rate of discontinuation and improve the safety profile ... both cohorts had similar discontinuation rates and safety profiles,” Dr. Motzer noted.
A quality of life analysis for the 600-mg group using the 19-item Functional Assessment of Cancer Therapy (FACT) Kidney Symptom Index (FKSI-19) showed values were consistently lower with the drug than with placebo during treatment, with a crossing of the threshold for a minimally important difference at week 8.
Pharmacokinetic analyses from the trial, reported in a poster at the meeting (Abstract 4564), showed that in the group starting pazopanib at 600 mg, disease-free survival was longer in patients who achieved higher drug trough concentrations at week 3 or 5.