Scientists find an immunomodulatory drug that could stop the deadly spread of skin cancer

Results of the pembrolizumab trial show a reduction in the risk of the cancer spreading

The randomized phase III STAMP trial is the largest study to date evaluating pembrolizumab as adjuvant treatment for Merkel cell carcinoma after tumor removal. After two years, 73% of patients who received pembrolizumab remained cancer-free, compared to 66% in the group that did not receive the drug. Although this difference was not statistically significant, those treated with pembrolizumab had a 42% lower chance of developing distant metastases, meaning the cancer had spread to areas such as the liver, lungs or bones.

Expert opinion: ‘Much needed good news’ for patients

“The STAMP trial provides the first evidence that pembrolizumab immunotherapy after surgery may help people with Merkel cell carcinoma by preventing the cancer from returning to organs considered distant from the original disease site,” said lead researcher Janice M. Meinert, MD, is co-chair of the ECOG-ACRIN Skin Cancer Committee and director of skin cancer and cutaneous oncology at NYU Langone Health’s Perlmutter Cancer Center. “This is much-needed good news for people with the highly aggressive cancer Merkel cell carcinoma,” Dr. Meinert added.

Understanding Merkel cell carcinoma

Merkel cell carcinoma is a rapidly progressing cancer that begins in skin cells that are sensitive to touch, and often appears as a hard, painless lump in areas frequently exposed to sunlight. Although skin cancer is the most common type of cancer in the United States, Merkel cell carcinoma — also known as neuroendocrine carcinoma of the skin — is extremely rare, affecting no more than three in a million people each year. It is very aggressive, with less than half of patients surviving five years after diagnosis.

Large-scale collaboration enables study of rare cancer

The STAMP trial (NCT03712605) enrolled 293 patients between 2018 and 2023, all of whom underwent surgery to remove their tumors. Of these, 147 patients were randomly assigned to receive pembrolizumab infusions after surgery, while 146 patients were monitored without additional drug therapy. Some participants also received radiation therapy as recommended by their doctors.

Because Merkel cell carcinoma is so uncommon, Dr. Meinert noted that national collaboration was crucial to making the study possible. Supported by the National Cancer Institute (NCI), part of the National Institutes of Health (NIH), ECOG-ACRIN conducted the trial through the National Cancer Institute’s National Clinical Trials Network, which included more than 500 hospitals and cancer centers across the country.

How does pembrolizumab work?

Pembrolizumab belongs to a class of immunotherapies known as PD-1 inhibitors. It works by blocking the PD-1 receptor, a protein that cancer cells use to hide from immune system attack. By interrupting this process, pembrolizumab helps immune cells recognize and destroy cancer cells more effectively. The US Food and Drug Administration has already approved pembrolizumab (brand name KEYTRUDA) for the treatment of locally advanced or recurrent metastatic Merkel cell carcinoma.

Overall survival, the other primary endpoint of the trial, continues to be monitored and will be reported at a later date.

Dr. Meinert will present the trial at the European Society for Medical Oncology (ESMO) Congress 2025 on Monday, October 20 in Berlin, Germany.