Monotherapy Pembrolizumab Demonstrates Historic Response for Rare Skin Cancer

Monotherapy with pembrolizumab (Keytruda; Merck) demonstrated a clinical response of 89% for individuals with unresectable metastatic desmoplastic melanoma, according to the results of a phase 2 clinical trial (NCT02775851), which were presented at the American Association for Cancer Research Annual Meeting 2023, held from April 14 to April 19 in Orlando, Florida.

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“Recent advances have led to a variety of treatment options for patients with melanoma, whether it be single-drug therapy or combination therapies,” Kari Kendra, MD, PhD, a professor of medicine and the director of cutaneous oncology at The Ohio State University Comprehensive Cancer Center’s Arthur G. James Cancer Hospital and Richard J. Solove Research Institute, said in a statement. “The question clinicians are now posed with is how we decide the best approach for any given patient, which requires an understanding of which patient populations and/or tumor types respond to different treatments.”

Investigators conducted the prospective phase 2 trial to evaluate the efficacy of pembrolizumab, which is an inhibitor of the PD-1/PD-L1 immune checkpoint, following findings that suggest a high response for individuals treated with an immune checkpoint inhibitor.

Although pembrolizumab is approved for the first-line treatment of individuals with unresectable metastatic melanoma, this is the first prospective trial testing the drug in individuals with desmoplastic melanoma subtype.

Investigators included individuals with genetically and histologically confirmed desmoplastic melanoma who had not received prior systemic therapy and were assigned to 1 of 2 cohorts. Cohort A evaluated neoadjuvant pembrolizumab in individuals with resectable disease, and cohort B evaluated pembrolizumab in individuals with unresectable metastatic disease.

Although there were previous reports of the neoadjuvant treatment, showing a 59% pathological complete response rate (CRR), for cohort A, the investigators recently reported findings from cohort B.

A total of 27 individuals with unresectable metastatic desmoplastic melanoma were enrolled in cohort B and received pembrolizumab as a monotherapy every 3 weeks for 2 years, or until disease progression or unacceptable toxicity.

The primary endpoint was CRR with secondary endpoints of overall survival (OS), progression-free survival (PFS), and safety.

There was an objective response rate of 89%, with 9 complete responses and 15 partial responses. The primary endpoint was met with a 33% CRR, which exceeded the threshold of 20%. Just 6 individuals experienced grade 3 or higher adverse events.

“The high responses to pembrolizumab monotherapy indicate that first-line combination therapy may not be necessary for patients with desmoplastic melanoma, which could help patients avoid unnecessary toxicities,” Kendra said. “It is important to keep studying rare diseases and rare subsets of more common diseases so that we can better tailor therapy to each individual.”

Investigators also suggested that this study exceeded response rates to those of historical data for patients with other melanoma subtypes.

They also said that this could help with the diagnosis of desmoplastic melanoma, being used as a predictive biomarker for patients who might be able to use pembrolizumab as a monotherapy increase of combining therapies.

Investigators plan to continue to evaluate the long-term efficacy of pembrolizumab in this trial, specifically for OS and PFS.

There are additional ongoing studies aimed at examining the molecular features of the tumor that progressed, following treatment with pembrolizumab, to identify biomarkers of treatment resistance.

Investigators noted that the small sample size is a limitation to the study.

Reference

Single-agent pembrolizumab may benefit patients with rare type of skin cancer. American Association for Cancer Research. News release. April 16, 2023. Accessed April 7, 2023. Email.