Keytruda (pembrolizumab) is an immunotherapy drug developed by Merck and approved to treat certain advanced types of cancers such as non-small cell lung cancer (NSCLC), melanomas and head and neck cancer.

The drug is also being tested for the treatment of mesothelioma, a rare type of cancer with no known cure. Mesothelioma affects mainly the thin protective lining tissue that covers the lungs and abdomen.

How Keytruda works

T-cells are a type of immune cells that detect and fight infections and diseases, including cancers. The immune system controls the activity of T-cells through the PD-1 (programmed death 1) pathway. However, some cancer cells take control of the PD-1 pathway to hide from T-cell attacks.

It works by blocking the PD-1 pathway, helping the immune system detect and fight cancer cells. The PD-1 protein is used as a biomarker to help predict the patient’s response to Keytruda. Mesothelioma cancers express the same protein and Keytruda may, therefore, potentially treat this type of cancer.

The U.S. Food and Drug Administration (FDA) granted accelerated approval to Keytruda in May 2017 for the treatment of any solid tumor carrying a specific biomarker — marking the first time the FDA grants a drug treatment based on a biomarker, or the genetic feature of a tumor, rather than its location in the body.

Keytruda studies

After Keytruda’s approval for the treatment of NSCLC, scientists started to analyze the drug’s potential for other types of cancers, including mesothelioma.

The first results of a Phase 1 study (NCT02054806, known as Keynote-28) showed that 76 percent of mesothelioma patients responded to Keytruda. Mesothelioma tumors stopped growing temporarily in half of the patients, and began shrinking in about one-fourth of patients studied.

In March 2017, Merck announced that the treatment showed a good safety profile. In 40 percent of participants, the disease was stable for six months or more. The results, published in the medical journal The Lancet Oncologysupport other studies of Keytruda in mesothelioma.

A Phase 1/2 (NCT02758787) trial is now recruiting participants with advanced solid malignancies. Its aim is to evaluate the safety, tolerability and preliminary activity of the combination therapy Keytruda and defactinib. This study will test whether defactinib can remove a barrier of immune cells misled into protecting cancer cells, while Keytruda activates cancer-killing immune cells to attack newly exposed cancer cells.

Merck is currently evaluating Keytruda in about 500 clinical studies that include more than 30 tumor types. In mesothelioma, there are a number of studies open or about to recruit participants.

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