according to a presentation at the European Society for Medical Oncology Virtual Congress 2020.
MK-6482 is an oral inhibitor of hypoxia inducible factor-(HIF) 2-alpha. The drug previously showed favorable safety and antitumor activity in advanced RCC, Ramaprasad Srinivasan, MD, PhD, of the National Cancer Institute, Bethesda, Md., said when presenting data from the phase 2 trial.
Dr. Srinivasan noted that, in VHL disease, RCC occurs in 25%-60% of individuals and is a key cause of morbidity and shortened life expectancy despite aggressive treatment. HIF-2-alpha accumulation activates genes that drive tumor growth in VHL-associated RCC.
The primary objective of Dr. Srinivasan’s phase 2 study was to evaluate the efficacy of the HIF-2-alpha inhibitor MK-6482 (at 120 mg daily) for the treatment of VHL-associated RCC.
The study included 61 treatment-naive patients with VHL diagnoses based on germline mutations. All subjects had RCC and additional non-RCC lesions, including pancreatic (100%), central nervous system (CNS) hemangioblastoma (70.5%), and retinal lesions (26.2%).
The patients’ median age at baseline was 41 years (range, 19-66), and 52.5% were men. Most (82%) had an European Cooperative Oncology Group performance status of 0.
Efficacy and safety
At a median follow-up of 68.7 weeks, 56 patients were receiving ongoing treatment.
By independent central review, the overall response rate in target RCC lesions was 36.1% (all partial responses), with unconfirmed partial responses in 11.5% and stable disease in 62.3%. There was no progression in target lesions. Decreases in target lesion size were observed in 91.8% of patients.
The median time to response was 31.1 weeks (range, 11.9-62.3 weeks), and the median duration of response was not reached (range, 11.9-62.3 weeks). The 1-year progression-free survival rate was 98.3%.
“Promising clinical activity was observed with MK-6482 in treatment-naive patients with VHL-associated RCC,” Dr. Srinivasan said. He added that efficacy was durable in both RCC and non-renal lesions.
Complete responses were observed in 6.6% (4/61) of pancreatic lesions and 11.6% (5/43) of CNS hemangioblastomas. Partial response and stable disease rates in pancreatic lesions were 57.4% and 34.4%, respectively. Partial response and stable disease rates in CNS hemangioblastomas were 18.6% and 65.1%, respectively.
In the 16 patients with retinal lesions, 68.8% saw an improvement and 25% had stable disease. No progression was reported.
“MK-6482 was well tolerated and has a favorable safety profile,” Dr. Srinivasan noted.
Most patients (98.4%) had treatment-related adverse events (AEs), with anemia being the most common. Grade 3 AEs included anemia (6.6%), fatigue (4.9%), dyspnea (1.6%), and hypoxia (1.6%). One patient (1.6%) discontinued treatment because of grade 1 dizziness. There was one grade 4 AE and one fatal AE, but both were considered unrelated to study treatment.
Remaining questions and next steps
The challenge in managing VHL-associated RCC tumors is finding a balance between the risk of cancer dissemination and renal morbidity, said study discussant Cristina Suárez, MD, PhD, of Hospital Universitari Vall d’Hebron in Barcelona.
“There is no standard of care systemic treatment, and recruitment for clinical trials is challenging,” Dr. Suárez added.
While response rates in RCC lesions with MK-6482 were generally in line with the experience reported for sunitinib and pazopanib, response rates were particularly favorable with MK-6482 in pancreatic lesions and CNS hemangioblastomas, Dr. Suárez said.
“These are the best response rates reported in non-RCC lesions,” she noted.
However, Dr. Suárez said, important questions remain. Specifically, how long should patients continue on treatment, and will lesion rebound occur after treatment discontinuation?
Larger multicenter trials are needed, Dr. Suárez said, pointing out that the current study is the largest to date of systemic therapy for patients with VHL disease.
The study was funded by Merck Sharp & Dohme Corp. Dr. Srinivasan disclosed funding from Merck and Calithera Biosciences. Dr. Suárez disclosed relationships with Astellas, AstraZeneca, Bayer, and many other companies.
SOURCE: Srinivasan R et al. ESMO 2020. Abstract LBA26.