A new cancer clinical trial by the ECOG-ACRIN Cancer Research Group (ECOG-ACRIN) shows that a drug that utilizes the body's immune system to target and eliminate cancer cells appeared to reduce the risk of distant metastases for an aggressive form of skin cancer when given immediately after surgery, but did not significantly reduce the overall risk of recurrence, which was a co-primary endpoint of the trial. The randomized phase 3 STAMP trial (EA6174) is the largest clinical study to date evaluating pembrolizumab, an anti-PD-1 therapy, as adjuvant therapy for Merkel cell carcinoma following surgical removal of the tumor.
The STAMP trial found that after two years, 73% of patients receiving pembrolizumab showed no cancer recurrence, compared with 66% among those who did not receive the drug. Although this difference did not reach statistical significance, patients receiving pembrolizumab had a 42% lower risk of developing distant metastases—cancer spreading to organs such as the liver, lungs, or bones – which was a secondary objective of the study.
"The STAMP trial provides the first evidence that immunotherapy with pembrolizumab after surgery may help people with Merkel cell carcinoma by preventing their cancer from returning in organs considered distant from the site of the original disease," said lead investigator Janice M. Mehnert, MD, co-chair of the ECOG-ACRIN Melanoma Committee and director of Melanoma and Cutaneous Medical Oncology at NYU Langone Health's Perlmutter Cancer Center. "This is much-needed good news for people who are living with the highly aggressive cancer that is Merkel cell carcinoma," Dr. Mehnert added.
Merkel cell carcinoma is a fast-growing cancer that begins in the skin's sensory cells, often appearing as a single, painless bump on sun-exposed areas. Although skin cancer is by far the most common type of cancer in the United States, Merkel cell carcinoma, also called neuroendocrine carcinoma of the skin, is highly uncommon, occurring in no more than three out of one million people annually. It is extremely aggressive, with fewer than half of patients surviving 5 years after diagnosis.
The phase 3 multicenter study (NCT03712605) was conducted from 2018 to 2023 and involved 293 patients whose tumors had been surgically removed. Of these, 147 were randomly assigned to receive pembrolizumab infusions after surgery, while 146 were observed without additional drug therapy. Some participants also received radiation as advised by their physicians.
Because Merkel cell carcinoma is a rare tumor, Mehnert emphasized that national collaboration is essential for recruiting patients for a trial of this scale. Supported by the National Cancer Institute (NCI), part of the National Institutes of Health (NIH), ECOG-ACRIN opened the study at over five hundred hospitals and cancer centers nationwide, through the NCI's National Clinical Trials Network.
Pembrolizumab is a type of immunotherapy known as a PD-1 inhibitor. Its mechanism of action involves blocking the PD-1 protein receptor, which cancer cells exploit to evade immune attack. Pembrolizumab allows immune cells to detect and attack tumors more effectively. It is approved by the U.S. Food and Drug Administration (brand name KEYTRUDA®) for treating recurrent locally advanced or metastatic Merkel cell carcinoma.
Overall survival, the other co-primary endpoint of the trial, continues to be followed and will be reported at a later date.
Dr. Mehnert will present the trial at the European Society for Medical Oncology (ESMO) 2025 Congress on Monday, October 20 in Berlin, Germany.
About ECOG-ACRIN
The ECOG-ACRIN Cancer Research Group (ECOG-ACRIN) is a membership-based scientific organization known for advancing precision medicine and biomarker research through its leadership of major national clinical trials that integrate innovative genomic approaches. Nearly 21,000 member researchers and advocates from approximately 1,400 academic medical centers and community hospitals collaborate across over forty scientific committees to design studies spanning the cancer care spectrum, from early detection to management of advanced disease.
KEYTRUDA® is a registered trademark of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA
