Testing for PD-L1 expression in malignant peritoneal mesothelioma may offer insight into whether patients of this rare cancer are candidates for immunotherapy, such as checkpoint inhibition. Immunotherapy has proven beneficial in other types of mesothelioma. A new study examines it as a possible treatment for peritoneal mesothelioma patients as well.

What Is PD-L1 Expression?

Programmed death-ligand 1 (PD-L1) is a protein that is found in high levels on certain types of cancer cells. The protein binds to and then blocks the PD-1 receptor on T-cells, which are the cells that detect and destroy cancer in the body.

PD-L1 expression is a measure of the amount of protein that is present. When tumor cells have high levels of PD-L1, they can fool the body into thinking they are not harmful. This allows the cancer to spread, unchecked by the body’s immune system.

Because of this relationship, PD-L1 expression is used to predict which cancer patients are most likely to benefit from an experimental treatment called immunotherapy. Immunotherapy uses immune checkpoint inhibitors to target PD-L1 proteins that are tricking the body against destroying them.

Generally speaking, if a tumor has high levels of PD-L1, a patient may be started on immunotherapy. Without increased PD-L1 expression, a patient may be deemed ineligible for immunotherapy.

This is of critical importance to cancer patients because immunotherapy has shown to be effective in the fight against certain terminal cancers. It also has fewer negative side effects than traditional cancer treatments.

It is only recently that malignant mesothelioma patients have been treated with immunotherapy. Even then, immunotherapy is usually only used to treat the more common form, malignant pleural mesothelioma.

In an exciting new study conducted at Rutgers Cancer Institute, researchers performed tests to find out if PD-L1 expression in peritoneal mesothelioma patients was elevated. If PD-L1 levels are, in fact, elevated, it could mean a breakthrough new treatment option for patients of the deadly disease.

What Is Malignant Peritoneal Mesothelioma?

Malignant peritoneal mesothelioma is a very rare cancer of the abdomen that has been linked to toxic levels of asbestos exposure. It is the second most common type of mesothelioma.

Peritoneal mesothelioma usually spreads extensively, ravaging the abdominal cavity. Since it is so rare and the symptoms are not well defined, it is usually not diagnosed until it is far too late to treat.

Peritoneal mesothelioma is a terminal cancer, with death being caused by:

  • Complications in the abdomen
  • Spreading of the cancer to other parts of the body
  • Starvation

For patients who are treated, cytoreductive surgery (CRS) with heated intraperitoneal chemotherapy (HIPEC) is usually performed. Sadly, without treatment, the life expectancy for peritoneal mesothelioma patients is less than one year.

Why Is PD-L1 Important to Peritoneal Mesothelioma Patients?

PD-L1, or checkpoint inhibition, is used to successfully treat many other types of cancer. Recent clinical trials have even found it to be beneficial for malignant mesothelioma. However, the number of peritoneal mesothelioma patients included in these studies has historically been very small.

“Peritoneal mesothelioma is a rare and lethal cancer for which there are limited treatment options. Because of its rarity, it is a generally understudied cancer.”

- H. Richard Alexander, Jr., MD, FACS, Chief Surgical Officer, Chief of Surgical Oncology at Rutgers Cancer Institute

Because of this, PD-L1 expression in peritoneal mesothelioma has not yet been identified. Since checkpoint inhibition has shown promise for other types of mesothelioma, its possible role in treating peritoneal mesothelioma may offer patients new hope.

Results of PD-L1 Expression Study in Peritoneal Mesothelioma

In the Rutgers Cancer Institute study, researchers looked at PD-L1 expression in 20 malignant peritoneal mesothelioma patients who had already had either systemic and/or peritoneal chemotherapy.

The PD-L1 data for those 20 patients was compared with that of patients who hadn’t had treatment. To do this, researchers examined tissues from the tumor biopsies or resections of existing patient samples over various points in time.

Some highlights of the results include:

  • Almost 75% of the tumors evaluated overexpressed PD-L1 proteins
  • In mesothelioma cells with the highest PD-L1 expression, patients did not live as long as patients with no PD-L1 expression
  • PD-L1 expression was lower in patients who had received prior chemotherapy as compared to those who hadn’t been treated

The implications of using PD-L1 expression as a biomarker in malignant peritoneal mesothelioma are promising.

The Future of PD-L1 in Peritoneal Mesothelioma

The plan moving forward is to test immunotherapy in peritoneal mesothelioma to determine its effectiveness in reducing tumor activity.

“We are excited for checkpoint inhibition to be an effective treatment option for patients with this rare cancer.”

- A senior author of the Rutgers study

The full results of the study will be shared at the Society of Surgical Oncology 2021 International Conference on Surgical Cancer Care virtual meeting.

In the meantime, PD-L1 expression in peritoneal mesothelioma has become a promising development in future treatment options.

The advocates at Mesothelioma Hope can inform patients and families about developments like this one. Contact us in confidence to find out more.

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Laura WrightWritten by:

Lead Editor

Laura Wright is a journalist and content strategist with more than 15 years of professional experience. She attended college at the University of Florida, graduating magna cum laude with a bachelor’s degree in journalism in 2008. Her writing has been featured in The Gainesville Sun and other regional publications throughout Florida.

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  1. Kim, J., Bhagwandin, S., & Labow, D. M. (2017). Malignant peritoneal mesothelioma: a review. Annals of translational medicine, 5(11), 236. Retrieved April 2, 2021 from https://doi.org/10.21037/atm.2017.03.96

  2. Ribas, A., & Hu-Lieskovan, S. (2016). What does PD-L1 positive or negative mean?. The Journal of experimental medicine, 213(13), 2835–2840. Retrieved April 2, 2021 from https://doi.org/10.1084/jem.20161462

  3. Rutgers Cancer Institute of New Jersey (2021). Exploring PD-L1 Expression in Malignant Peritoneal Mesothelioma. Retrieved April 2, 2021 from https://www.newswise.com/articles/exploring-pd-l1-expression-in-malignant-peritoneal-mesothelioma

  4. White, M.G., Schulte, J.J., Xue, L., et al. Heterogeneity in PD-L1 expression in malignant peritoneal mesothelioma with systemic or intraperitoneal chemotherapy. Br J Cancer 124, 564–566 (2021). Retrieved April 2, 2021 from https://doi.org/10.1038/s41416-020-01130-x

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