Checkpoint Inhibitor Drugs for Peritoneal Mesothelioma?

Checkpoint inhibitor immunotherapy works for malignant mesothelioma, specifically when the disease forms near the lungs.

There’s another type of mesothelioma, usually understudied and analyzed, left out of this discussion. New research aims to provide confidence that immunotherapy for mesothelioma can help patients with this rare cancer as well.

The Rutgers Cancer Institute of New Jersey hosted a study on the efficiency of immune checkpoint inhibitor drugs for peritoneal mesothelioma. This type of mesothelioma forms in the peritoneum, the thin lining that circles the abdominal cavity.

It’s much rarer than pleural mesothelioma, which is near the lungs. There are fewer than 1,000 peritoneal mesothelioma cases per year, which makes clinical studies and reviews much tougher.

Dr. Richard Alexander, the chief surgical officer and chief of surgical oncology at Rutgers Cancer Institute, and his team found some answers.

 

Results From the Rutgers Cancer Institute Study

The purpose of the study was to determine if peritoneal mesothelioma tumors expressed high levels of the PD-L1 protein. This protein subdues the immune system by engaging T-cells through the PD-1 protein receptor.

Some immune checkpoint inhibitor drugs, like Keytruda and Opdivo, block the PD-L1 protein. The drugs allow the immune system to operate as normal, seeking and attacking unwanted diseases like mesothelioma.

Oncologists and mesothelioma specialists know from years of data that PD-L1 is highly expressed in most cases of pleural mesothelioma. Dr. Alexander confirmed the same for peritoneal mesothelioma.

According to the report on the Rutgers Cancer Institute website, he and his team identified 24 samples from 20 peritoneal mesothelioma patients evaluated and treated at the hospital within the past three years. They used a PD-L1 stain (Dako 22c3) to reveal the protein in samples.

From the 24 samples, 19 were above the threshold for PD-L1 overexpression. This equates to more than 75% of the samples.

They also learned that PD-L1 overexpression is an indicator of poor survival. As the team increased the threshold for PD-L1 overexpression, the survival times changed:

• The median survival for the 20 patients was 110 months (around nine years).
• When the threshold increased, the PD-L1 overexpressed patients had a median survival of just 49 months.

 

What Does This Mean?

Peritoneal mesothelioma patients have two treatment options: surgery or chemotherapy. The former is the best hope for survival, but many patients aren’t candidates for surgery. They’re left with just one option, which has uncomfortable side effects and low survival rates.

Dr. Alexander’s findings reveal a new potential therapy: immunotherapy drugs. Checkpoint inhibitors have fewer side effects than chemotherapy and have improved survival times for pleural mesothelioma patients.

The same could be true for the small subset of people with peritoneal mesothelioma.

“Our plan will be to test checkpoint inhibition in patients prospectively to determine whether or not it is associated with significant antitumor activity,” Dr. Alexander wrote in the report.

For more information on immune checkpoint inhibitors or other immunotherapy drugs, contact our patient advocate Karen Ritter. She’s available via email at karen@mesotheliomaguide.com to discuss possible clinical trials for peritoneal mesothelioma patients.