A major new clinical study has found that a type of immunotherapy may help stop a rare and fast-growing skin cancer from spreading to other parts of the body.
The drug, pembrolizumab (brand name KEYTRUDA), was tested in patients with Merkel cell carcinoma, a rare but aggressive form of skin cancer.
The trial, called STAMP (EA6174), was run by the ECOG-ACRIN Cancer Research Group and looked at how well the drug worked when given shortly after surgery to remove tumors.
Merkel cell carcinoma is a type of cancer that starts in the skin’s nerve-like cells. It often appears as a painless bump in areas exposed to the sun and is one of the most aggressive skin cancers, with fewer than half of patients living more than five years after diagnosis.
Because it is so rare—affecting fewer than three in a million people each year—it has been difficult to study in large numbers.
The STAMP trial is the biggest study so far to test pembrolizumab after surgery for this cancer. From 2018 to 2023, the trial enrolled 293 people who had recently undergone surgery to remove their tumors.
Half of them received pembrolizumab infusions, while the other half were monitored without drug treatment. Some patients in both groups also received radiation therapy, depending on their doctor’s advice.
After two years, 73% of patients who got pembrolizumab remained free of cancer, compared to 66% in the group that did not get the drug.
Although this difference was not large enough to be called statistically significant, the study found that pembrolizumab did reduce the risk of cancer spreading to distant organs—like the liver, lungs, or bones—by 42%. This reduction in distant metastases was a key goal of the trial.
Dr. Janice Mehnert, the lead investigator of the trial, said the results offer hope for people with Merkel cell carcinoma. She explained that pembrolizumab may help prevent the cancer from coming back in distant parts of the body, which is especially important for this aggressive cancer.
Dr. Mehnert is also the director of Melanoma and Cutaneous Medical Oncology at NYU Langone Health’s Perlmutter Cancer Center.
The drug pembrolizumab is already approved by the U.S. Food and Drug Administration (FDA) to treat advanced Merkel cell carcinoma that has come back or spread. It belongs to a group of treatments called PD-1 inhibitors.
These drugs help the immune system work better by blocking a protein that cancer cells use to hide from immune attack. When this protein is blocked, immune cells are more likely to detect and destroy cancer cells.
The STAMP trial was made possible through a large national effort. Over 500 hospitals and cancer centers across the United States participated, thanks to the support of the National Cancer Institute (NCI), which is part of the National Institutes of Health (NIH).
Because Merkel cell carcinoma is so rare, working together on a national level was necessary to collect enough data.
The study did not show a major difference in the overall risk of cancer returning, but it did find promising signs that pembrolizumab could stop the disease from spreading far from the original tumor site. The trial is continuing to follow patients to see if the drug helps them live longer, with those results expected in the future.
Dr. Mehnert was present the full results at the European Society for Medical Oncology (ESMO) 2025 Congress in Berlin, Germany.
If you care about skin health, please read studies about eating fish linked to higher risk of skin cancer, and Vitamin B3 could help prevent skin cancers.
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