Two Breast Cancer Approvals in One Month: What an ESR1 Mutation Means

The FDA keeps a running list of the cancer drugs it has approved. Read on September 23, 2026, that list carries two September entries for the same fairly narrow group of patients: people with advanced breast cancer that is hormone-receptor positive, HER2 negative, and carries a change in a gene called ESR1.

The list shows camizestrant (brand name Etcamah) on September 4, 2026, given accelerated approval for use with a CDK4/6 inhibitor, and imlunestrant (Inluriyo) with abemaciclib (Verzenio) on September 18, 2026, for advanced or metastatic disease with an ESR1 mutation.

Two entries in one month for one mutation is unusual enough to be worth explaining. Most of what is useful here is not the drug names. It is the word ESR1.

What hormone therapy is doing in the first place

Most breast cancers are "hormone-receptor positive." That means the cancer cells have a docking point — a receptor — that the hormone estrogen fits into, and estrogen tells them to grow.

Hormone therapy takes that signal away. The National Cancer Institute describes hormone therapy as treatment that "slows or stops the growth of cancer that uses hormones to grow," either by lowering how much hormone the body makes or by blocking how the hormone works. For many people it works well, and it can work for years.

Where ESR1 comes in

ESR1 is the gene that carries the instructions for building that estrogen receptor.

Over time, in some people, a cancer that has been treated with hormone therapy picks up a change — a mutation — in that gene. The receptor it builds afterward can behave as though estrogen were switched on even when the drug has taken the estrogen away. The old treatment stops holding the cancer back.

That is a resistance problem, not a new cancer. And it is the specific problem these September approvals are aimed at: drugs meant for breast cancer that has an ESR1 mutation, after hormone therapy has stopped doing its job.

Whether a person's cancer has an ESR1 mutation is not something anyone can tell by looking. It is found by testing — the same general idea NCI describes for targeted therapy, where "your tumor will need to be tested to see if it contains targets for which there is a drug." Some of this testing is done on a blood sample rather than on tissue.

What "accelerated approval" means

One of the two September entries, camizestrant, is listed as an accelerated approval. That is a different thing from a standard approval, and the difference matters to patients.

An accelerated approval lets a drug reach people earlier, based on an early measure that is expected to predict real benefit — usually whether tumors shrank — rather than on proof that people lived longer. The trials that would confirm the longer-term benefit are meant to continue afterward. Sometimes they confirm it. Sometimes they do not, and the approval is withdrawn.

So "approved" is real, and it is not the same as "settled."

What this does not mean

• It does not mean a new option for most people with breast cancer. Both entries describe a specific group: hormone-receptor positive, HER2 negative, ESR1 mutated, advanced or metastatic. That is a minority of breast cancer, reached after other treatment.
• It does not tell you these drugs help people live longer. The FDA's list records what was approved and for whom. It is not a summary of survival results, and we did not read trial results here. An accelerated approval in particular is granted before that question is answered.
• It does not mean anyone should ask to switch treatment. A change in treatment depends on the individual cancer, on what has already been tried, and on test results. Nothing on this page is a recommendation.
• It does not tell you what these drugs feel like to take. Side effects, monitoring and cost are all real parts of the decision, and none of them appear in a one-line approval listing.

What to ask a healthcare team

• Has my cancer been tested for an ESR1 mutation, and if not, is that test worth doing now?
• If the test is positive, does that change what options are on the table for me?
• Is this a standard approval or an accelerated one, and what is still being studied?
• What would we watch to know whether a change in treatment is working?

How this article was prepared

An AI-assisted editorial system helped prepare this page from the FDA's published oncology approval notifications list and National Cancer Institute patient pages on hormone therapy and targeted therapy, each opened on the source-check date shown above. No named medical reviewer has reviewed it unless one is listed.

Cancer Explained is published by the National Cancer Information Foundation. It is not medical advice and does not suggest a test or treatment.

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