E. Shyam P. Reddy, Professor and Director of the Cancer Biology Program at Morehouse School of Medicine, Adjunct Professor at Winship Cancer Institute of Emory University, shared on LinkedIn:
“From today, the Australian government will expand Pharmaceutical Benefit Scheme (PBS) access to the drug Keytruda for three additional types of cancer.
These three conditions will be covered as part of a multi-cancer listing for people with advanced and high-risk cancers, allowing clinicians to prescribe the drug to treat more types of advanced cancers.
This is part of a broader shift away from cancer treatment with traditional chemotherapy drugs that can be less effective and have more intense side effects.
So what is Keytruda? How does it work? And which cancers can it treat?
The problems with standard chemo
Most chemotherapy drugs developed in the 1950s to 1990s are small molecules that scientists refer to as cytotoxics. This means they mess with the internal processes of cancer cells so much that the cancers essentially shut themselves down.
But cytotoxics can’t tell the difference between cancerous and healthy cells. So they attack all fast-growing cells. Cancers are comprised of fast-growing cells, but so is the lining of the gastrointestinal tract, bone marrow and hair.
Damage to these healthy cells leads to the typical chemotherapy side effects many patients experience.
Damage to the stomach and intestines causes nausea, vomiting and diarrhea.
Bone marrow damage leads to lethargy because of low red blood cell numbers. Low levels of white blood cells increase susceptibility to infection.
Hair loss occurs not just on the head and body but also in the ears, which can cause hearing loss.
The intensity of the side effects limits the amount of cytotoxic drugs that can be given to a patient. This in turn limits how successful that drug is in treating the cancer.
Don’t let yourself be misled. Understand issues with help from experts.
How Keytruda is different
Unlike the small-molecule cytotoxics, Keytruda (pembrolizumab) is a large protein-based drug from a family of medicines called monoclonal antibodies.
Monoclonal antibodies are highly selective for cancer cells, and harm healthy cells much less than cytotoxics. Their side effects therefore tend to be milder, although doctors still need to manage them.
To understand how Keytruda works, we need to know about the protein PD-1. This is a protein the body uses as an immune system brake to stop itself attacking healthy cells.
But some cancers express a protein on their surface called PD-L1, which stops immune system T-cells with PD-1 from attacking the cancer.
PD-1-targeting drugs, including Keytruda, work by blocking PD-L1’s interaction with PD-1. This turns the immune system back on so the body can fight the cancer itself.
Keytruda was the first in its class to do this.
You can also read: Merck and Moderna’s Intismeran Autogene Plus Keytruda Meets Phase 3 RFS and DMFS Endpoints in Resected Melanoma
