Keytruda® cuts distant spread in a rare aggressive skin cancer

Anatomy of the skin showing the epidermis, dermis, and subcutaneous tissue. Merkel cells are in the layer of basal cells at the deepest part of the epidermis and are connected to nerves. – Image credit National Cancer Institute copyright 2008 Therese Winslow

CANCER DIGEST – Dec. 20, 2025 – Patients with a rare skin cancer who received an immunotherapy drug after surgery had a 42 percent lower risk of the cancer spreading to other parts of the body, results of a large clinical trial show.

The clinical trial led by the ECOG-ACRIN Cancer Research Group involved 293 patients enrolled between 2018 and 2023 in the STAMP clinical trial. All had been treated with surgery for a type of aggressive skin cancer, called Merkel Cell Carcinoma, a fast-growing cancer of the skin’s sensory cells. The results were presented Oct. 20, 2025 at the European Society for Medical Oncology (ESMO) annual meeting.

Often called neuroendocrine carcinoma of the skin, it appears as a single, painless bump on sun-exposed areas of skin. It is diagnosed in fewer than 3,000 people annually but is extremely deadly with fewer than half of patients surviving five years after diagnosis.

In the large multi-center comparison trial, 147 patients were randomly assigned to receive the immunotherapy drug pembrolizumab (KEYTRUDA^®) after surgery and 146 patients received surgery alone. The primary aim of the comparison trial was to see if pembrolizumab would cut recurrence and extend overall survival. 

After two years, 73 percent of patients receiving pembrolizumab showed no recurrence compared to 66 percent of those in the surgery only group. While that difference was not considered statistically significant, a secondary endpoint showed that the pembrolizumab group was 42 percent less likely to have the cancer spread to the liver, lungs or bones, which is considered a significant improvement in distant metastasis-free survival. 

“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 of New York University Langone Health’s Perlmutter Cancer Center in a press release. “This is much-needed good news for people who are living with the highly aggressive cancer that is Merkel cell carcinoma."

Pembrolizumab is a type of immunotherapy that acts to block a protein receptor called PD-1 that cancer cells use to evade the immune system. The drug is FDA approved for treatment of certain lung cancers, melanoma, head and neck cancers, as well as bladder, stomach and kidney cancers, among others.

The overall survival results require longer followup and will be reported at a later date. The final study results will appear in the journal Annals of Oncology.

Source: ECOG-ACRIN Research Group press release