Exploring PD-L1 Expression in Malignant Peritoneal Mesothelioma

New Brunswick, N.J., March 19, 2021 – Peritoneal mesothelioma is a cancer that develops in the lining of the abdomen, which is known as the peritoneum. In a recent study from Rutgers Cancer Institute of New Jersey, researchers tested whether or not mesothelioma cancer cells express high amounts of PD-L1, a protein that is abundantly present on some types of cancer cells. The PD-L1 protein is an inhibitory molecule that binds to the PD-1 receptor on T-cells, which are cells known to have the ability to recognize and destroy cancer cells in the body.

Results of the work are being shared as a poster presentation at the Society of Surgical Oncology 2021 International Conference on Surgical Cancer Care virtual meeting. Senior author H. Richard Alexander, Jr., MD, FACS, chief surgical officer, chief of surgical oncology at Rutgers Cancer Institute and regional director of surgery for Monmouth Medical Center, an RWJBarnabas Health facility, shares more about the work.

Why is this topic important to study?

Researchers use inhibitors of PD-L1 to treat a broad array of different cancer types. This general type of treatment is called checkpoint inhibition. Recent studies have demonstrated anti-tumor activity in patients receiving PD-L1 blockade for malignant mesothelioma with PD-L1 expression. However, the number of patients with peritoneal mesothelioma in these studies was very small.

Therefore, the frequency of PD-L1 expression and the possible role of checkpoint inhibition in this type of cancer had not yet been characterized.

Describe the work and what you discovered.

In our study, we tested whether or not mesothelioma cancer cells express high amounts of PD-L1.  Peritoneal mesothelioma is a rare and lethal cancer for which there are limited treatment options.  Because of its rarity, it is a generally under studied cancer.  Using our biorepository of tissues, we were able to identify more than 20 patients with this rare condition that had been evaluated and treated at Rutgers Cancer Institute of New Jersey over the last three years. We used standard assays to quantitate the amount of PD-L1 present on these tumor cells and found that almost 75 percent of the tumors tested overexpressed this protein. We also showed that in tumors with the highest expression of PD-L1 that the patients did not survive as long as those who had tumors that did not express PD-L1.

What are the implications of these findings?  

The implications of our findings is that PD-L1 in patients with peritoneal mesothelioma may be inhibiting the immune system from recognizing the cancer and attacking it. We are excited for checkpoint inhibition to be an effective treatment option for patients with this rare cancer. Our plan will be to test checkpoint inhibition in patients prospectively to determine whether or not it is associated with significant antitumor activity.

Additional details can be found here.