Immune Drug Cuts Risk of Deadly Skin Cancer Spread After Surgery

Patients with Merkel cell carcinoma who received Keytruda (pembrolizumab) after surgery had a 42% lower risk of the cancer spreading to other organs, according to results from a nationwide clinical trial reported at the European Society for Medical Oncology (ESMO) 2025 Congress on October 20, 2025, in Berlin.

The phase 3 STAMP trial, led by Janice M. Mehnert, M.D., of NYU Langone Health's Perlmutter Cancer Center, enrolled 293 patients between 2018 and 2023 who had undergone surgery to remove their tumors. The study randomly assigned half the patients to receive Keytruda infusions following surgery, while the other half were monitored without additional drug treatment.

After two years, 73% of patients who received Keytruda remained cancer-free, compared with 66% in the observation group. While this difference was not statistically significant for the trial’s primary goal of reducing overall recurrence, the drug did show a meaningful benefit in preventing distant metastases, which is when cancer spreads to organs such as the liver, lungs or bones.

"The STAMP trial provides the first evidence that immunotherapy with Keytruda 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," Mehnert said in a news release.

Merkel cell carcinoma is a rare but highly aggressive skin cancer that develops in the skin’s touch-sensing cells and often appears as a firm, painless lump on sun-exposed areas. The disease affects no more than 3 in 1 million people each year in the United States, and fewer than half of patients survive five years after diagnosis.

Keytruda works by blocking the PD-1 receptor, a protein that cancer cells use to evade the immune system. By interrupting this process, the drug helps immune cells recognize and destroy cancer cells more effectively. The FDA approved Keytruda in 2018 to treat recurrent locally advanced or metastatic Merkel cell carcinoma

The therapy is also approved for many other cancers. Keytruda is now used to treat melanoma, lung cancer, bladder cancer, head and neck cancer, and several other solid tumors. It’s one of the most widely studied immunotherapies, with more than 1,600 ongoing trials testing its use in more than 30 different types of cancer, according to the drug’s maker, Merck. The drug’s broad reach reflects a shift in oncology care, where immune-based treatments are increasingly being used earlier in the disease process to help prevent recurrence or spread.

The STAMP trial, which is being supported by the National Cancer Institute, is the largest study to evaluate the drug as adjuvant therapy, which means treatment given after surgery to reduce the risk of cancer returning. Because Merkel cell carcinoma is so uncommon, the study required collaboration from more than 500 hospitals and cancer centers across the country. Some patients also received radiation therapy as recommended by their doctors.

The researchers are continuing to follow patients to assess overall survival, which is another primary goal of the trial and will be reported at a later date.

Mehnert said the results represent important progress for patients with this aggressive disease, noting that preventing distant spread is particularly significant because metastatic cancer is typically more difficult to treat and carries a worse prognosis.

"This is much-needed good news for people who are living with the highly aggressive cancer that is Merkel cell carcinoma," Mehnert said.