Merkel cell carcinoma has a high rate of metastasis and poor patient outcomes. The current standard of care for patients with recurrent, unresectable, or metastatic disease is immune checkpoint inhibitor monotherapy targeting PD-1 and PD-L1, but only about half of patients respond to this therapy. A research team is investigating a new dual checkpoint inhibitor therapy (ipilimumab and nivolumab) with or without stereotactic body radiation therapy. Results from the phase II clinical trial were published by Kim et al in The Lancet, in conjunction with a presentation at the European Society for Medical Oncology (ESMO) Congress 2022 (Abstract LBA42).

Fifty patients with unresectable, recurrent, or stage IV Merkel cell carcinoma were randomly assigned to two treatment groups: one group received ipilimumab, a checkpoint inhibitor targeting CTLA4, and nivolumab, an anti–PD-1/PD-L1 inhibitor. The other group was treated with the ipilimumab and nivolumab combination along with stereotactic body radiation therapy. Both groups had a mix of patients who had previously been treated with immune checkpoint inhibitor therapy targeting PD-1/ PD-L1 and some who had not received that type of therapy. The primary endpoint for this phase of the trial was objective response rate, defined as the percentage of patients whose tumors decreased or disappeared after receiving the therapy.

After an average 14.6 months of follow-up, 100% of patients who had not received previous immune checkpoint inhibitor therapy, regardless of the treatment group, responded to the investigational combination therapy, with 41% of patients having a complete response. Of the 26 patients who had received prior anti–PD-1/PD-L1 therapy, 8 responded to therapy, with 4 having a complete response.

“Our results show that first-line combination therapy with nivolumab and ipilimumab has a high overall response rate with durable responses for patients with advanced Merkel cell carcinoma,” said Sungjune Kim, MD, PhD, principal investigator of the trial and Associate Member of the Radiation Oncology Department at H. Lee Moffitt Cancer Center and Research Institute. “This presents a new option for patients who may not respond to the current standard of care therapy for this disease.”

Dr. Kim added that the addition of stereotactic body radiation therapy did not improve efficacy of the nivolumab and ipilimumab combination therapy.

Disclosure: This trial was supported by the Bristol Myers Squibb Rare Population Malignancy Program, the National Cancer Institute, and the Moffitt Foundation. For full disclosures of the study authors, visit thelancet.com or oncologypro.esmo.org.