Targeting Mesothelioma PD-L1 Protein Could Be Game Changer

The mesothelioma growing on the lining of your lungs could be vulnerable to a devastating attack through a pathway provided by an obscure cellular protein.

Scientists raised this possibility just over a month ago at the annual meeting of the European Society for Medical Oncology in Madrid, Spain.

The pathway exists because mesothelioma cells in about 20 percent of patients manufacture a protein called PD-L1, short for programmed cell-death ligand 1.

PD-L1 is bad news for those patients because this protein contributes to a faster decline in health and a faster approach of death.

As such, PD-L1 could serve as a good target for mesothelioma immunotherapy, say the researchers from Vall d’Hebron Institute Oncology in Barcelona, Spain.

Mesothelioma and Your Immune System

Your body’s immune system wants to — and has tried very hard to — defeat the mesothelioma stalking you from within. One reason it has been unable to succeed is PD-L1.

PD-L1 suppresses your body’s natural response to the presence of mesothelioma.

Instead of a full-throated attack, PD-L1 causes your immune system to do little more than fire a few shots across the bow before retreating to base.

The researchers propose targeting PD-L1 in order to block its action and thereby hobble its ability to prevent your immune system from properly functioning.

They’re confident of this strategy because they’ve seen indications that it works in melanoma and lung cancer patients.

In arriving at their conclusions about PD-L1 as a mesothelioma immunotherapy target, the researchers assessed tissue samples from 119 malignant pleural mesothelioma patients.

They studied the samples under the microscope with the aid of an anti-PD-L1 stain and then rated the intensity of PD-L1 expression on a scale of 0 to 3, with 3 being strongest.

Of the patients whose samples tested positive for PD-L1 expression, almost 19 percent scored a 3, while just over 56 percent scored a 1, meaning PD-L1 expression was weak.

Patients who scored 0 had no PD-L1 expression. They were found to have a median mesothelioma survival of approximately 16 months after diagnosis.

By contrast, the patients who scored 3 were found to have a median mesothelioma survival of not quite five months after diagnosis.

In other words, the stronger the intensity of your PD-L1 expression, the worse off you can expect to be.

The researchers said it did not matter whether those PD-L1-expressing mesothelioma patients were male or female, smokers or nonsmokers.

Nor did it matter that they suffered a little or a lot of asbestos exposure before the onset of mesothelioma.

Epithelioid Mesothelioma Is the Common Thread

However, the researchers did find a common thread.

They noted that PD-L1 expression was much less likely to occur in those patients whose mesothelioma was of the epithelioid type.

The researchers said their findings could offer hope of a new targeted immunotherapy treatment to PD-L1-expressing mesothelioma patients.

With that in mind, the researchers said an appropriate next step would be to investigate the use of so-called immune checkpoint inhibitors that target the PD-L1 pathway.

They explained that identifying the best antibody and platform to engage PD-L1 will no doubt prove challenging.

The European Society for Medical Oncology is one of the continent’s top professional organizations in the field of cancer treatment. The organization publishes the respected journal Annals of Oncology.