PROTACs and Targeted Protein Degradation: What the Cancer Research Means

Blocking a protein versus throwing it out

Most targeted drugs work by blocking. The drug sits on a protein and stops it from doing its job. As long as the drug stays put, the protein is quiet. When the drug leaves, the protein wakes up.

A PROTAC does something else. It does not block the protein. It marks it for destruction.

The name stands for proteolysis targeting chimera. Chimera means a molecule with two different ends joined together.

How the two ends work

NCI's drug entry for vepdegestrant describes the design in detail. One end binds the target protein. The other end grabs a piece of the cell's own disposal machinery, called an E3 ligase.

Holding both at once, the molecule lets the cell tag the target with a marker called ubiquitin. Tagged proteins are fed into the proteasome, the cell's shredder. The target is broken down.

Then the PROTAC lets go and does it again to another copy. That is the theoretical advantage. One molecule can remove many copies of a protein.

This idea is not brand new

Destroying a protein rather than blocking it already exists in breast cancer care. NCI describes a drug class called selective estrogen receptor degraders. They bind estrogen receptors and destroy them. Fulvestrant is one, and it has been approved for years.

Fulvestrant is given as an injection. PROTACs aim to do similar work with a pill, and to reach proteins that older drugs could not.

The one that reached approval

On May 1, 2026, the FDA approved vepdegestrant, sold as Veppanu. The indication is narrow. It covers adults with breast cancer that is estrogen receptor positive, HER2 negative, and carries an ESR1 mutation. The cancer must be advanced or metastatic, and it must have progressed after at least one line of endocrine therapy.

The mutation has to be found by an FDA-authorized test. The FDA approved a blood-based test alongside the drug for that purpose. Our page on biomarker testing explains how companion tests gate access to drugs like this.

Read the trial numbers carefully

The approval rests on VERITAC-2. It enrolled 624 adults. Of those, 270 had tumors with an ESR1 mutation. Participants were assigned at random to vepdegestrant by mouth or fulvestrant by injection.

In the ESR1-mutated group, median progression-free survival was 5 months with vepdegestrant and 2.1 months with fulvestrant. The response rate was 19 percent versus 4 percent.

Two things deserve equal weight. The difference was real and statistically significant. It was also measured in months, and overall survival data were still immature when the FDA reviewed the file. Nobody yet knows whether people live longer on this drug.

The label carries warnings for QTc interval prolongation, a heart rhythm effect, and for harm to a developing fetus.

What this does not establish

• One approval does not validate every PROTAC in development.
• Most PROTACs are still in early clinical trials, and most experimental drugs do not reach approval.
• Removing a protein can also remove functions healthy cells need.
• Proteins the cell keeps replacing may need continuous dosing anyway.

What to ask about this drug

• Does my tumor have the specific mutation this drug requires?
• What test finds it, and when was mine done?
• What is the expected benefit in my situation, in months?
• What are the heart-related monitoring requirements?
• What are the other options after endocrine therapy stops working?

How this article was prepared

An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.

The National Cancer Information Foundation publishes Cancer Explained. This page is for learning. It is not medical advice and does not suggest a test or treatment.

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