Camizestrant is an oral estrogen receptor antagonist belonging to the selective estrogen receptor degrader (SERD) class. It was developed by AstraZeneca for the treatment of certain forms of hormone receptor-positive breast cancer.

In the United States, camizestrant is marketed as ETCAMAH. The U.S. Food and Drug Administration granted accelerated approval on September 4, 2026, for a specific group of adults with hormone receptor-positive, HER2-negative locally advanced or metastatic breast cancer.

The approved use is restricted to patients in whom an ESR1 mutation is detected during treatment with an aromatase inhibitor and a CDK4/6 inhibitor. Detection must be performed using an FDA-authorized test.

What Is Camizestrant?

Camizestrant is an oral medicine that acts directly on the estrogen receptor. It is designed to block estrogen receptor signaling and promote degradation of the estrogen receptor within cancer cells.

This mechanism is particularly relevant to tumors that have developed an ESR1 mutation. These mutations can contribute to resistance to aromatase inhibitor treatment.

Unlike some older endocrine treatments, camizestrant does not have partial estrogen receptor agonist activity. It acts as an antagonist against both normal and mutated estrogen receptors.

When Is Camizestrant Used?

The current U.S. indication is relatively specific.

Camizestrant is used together with a CDK4/6 inhibitor in adults who have:

• Hormone receptor-positive breast cancer

• HER2-negative disease

• Locally advanced or metastatic disease

• An ESR1 mutation detected during aromatase inhibitor plus CDK4/6 inhibitor treatment

• Testing performed with an FDA-authorized diagnostic test

Patients must previously have received an aromatase inhibitor together with a CDK4/6 inhibitor for at least six months.

Camizestrant is not approved as a standalone treatment for this indication. The same CDK4/6 inhibitor being used when the ESR1 mutation is detected is continued, while the endocrine treatment is changed.

The Role of ESR1 Testing

One of the notable features of the camizestrant indication is the use of circulating tumor DNA (ctDNA) testing.

Rather than waiting for visible progression on imaging, an ESR1 mutation can be identified through a blood-based test. In the approved treatment strategy, serial testing is performed during treatment, with the aim of identifying an ESR1 mutation before radiographic disease progression.

The companion diagnostic identified in the U.S. approval is the Guardant360 CDx assay.

ESR1 mutations are generally acquired during the course of cancer treatment rather than being inherited mutations. The source document notes that they are uncommon at the initial diagnosis of metastatic hormone receptor-positive breast cancer but become considerably more frequent after progression on an aromatase inhibitor.

How Does Camizestrant Work?

Estrogen can stimulate the estrogen receptor and contribute to the growth of hormone receptor-positive breast cancer.

Aromatase inhibitors reduce the body's production of estrogen. However, some cancer cells acquire ESR1 mutations that can allow the estrogen receptor to remain active despite lower estrogen levels.

Camizestrant takes a different approach. It binds to the estrogen receptor, blocks its activity, and promotes degradation of the receptor. This provides a mechanism for targeting both normal and mutated forms of the receptor.

Dose and Administration

The recommended adult dose described in the U.S. prescribing information is 75 mg taken orally once daily.

It can be taken with or without food and should be taken at approximately the same time each day.

The tablet should be swallowed whole. It should not be cut, crushed, or chewed, and damaged tablets should not be used.

Camizestrant is administered together with abemaciclib, palbociclib, or ribociclib according to the approved treatment regimen.

Treatment is continued until disease progression or unacceptable toxicity.

Monitoring During Treatment

Because camizestrant can affect cardiac rhythm, monitoring is an important part of treatment.

The prescribing information recommends an ECG before treatment, followed by weekly ECG monitoring during the first two weeks and additional monitoring when clinically appropriate.

Serum electrolytes should also be assessed and abnormalities corrected.

Patients with a low resting heart rate or those taking medicines that reduce heart rate may require closer monitoring, particularly during the first month of treatment.

Vision should also be monitored because visual disturbances are among the adverse reactions associated with camizestrant.

Possible Adverse Effects

Clinical trial data indicate that camizestrant can cause several adverse reactions. Some of the more frequently reported effects include:

• Visual disturbances

• Fatigue

• Joint pain

• Dry eye

• Back pain

• Nausea

• Changes in blood cell counts

Laboratory abnormalities reported during treatment included reductions in neutrophils, white blood cells, hemoglobin, lymphocytes, and platelets. Changes in liver enzymes and creatinine were also reported.

The severity and clinical significance of these effects vary between patients.

Cardiac Safety

Camizestrant carries a boxed warning concerning the risk of cardiac arrhythmias when used with medicines that prolong the QT interval.

The combination with ribociclib requires particular attention because ribociclib can also prolong the QT interval and affects the metabolism of camizestrant.

Bradycardia, or a slower-than-usual heart rate, has also been reported.

Symptoms such as fainting, chest pain, palpitations, severe dizziness, or shortness of breath require prompt medical assessment.

Visual Changes

Visual disturbances were reported in 34% of patients receiving camizestrant with a CDK4/6 inhibitor in the SERENA-6 study.

Reported symptoms included blurred vision, flashes of light, double vision, changes in visual fields, reduced visual acuity, and sensitivity to light.

Patients who develop significant or persistent visual symptoms may require assessment by an eye-care professional.

Pregnancy and Breastfeeding

Camizestrant may cause fetal harm based on its mechanism of action and findings from animal studies.

Pregnancy status should be assessed before treatment in females of reproductive potential. The prescribing information recommends effective non-hormonal contraception during treatment and for four weeks after the final dose.

Breastfeeding is not recommended during treatment and for one week after the final dose because there are no adequate data regarding the presence of camizestrant in human milk or its effects on a breastfed infant.

Kidney and Liver Function

The prescribing information does not specify a renal dose adjustment for patients with creatinine clearance from 30 to less than 90 mL/min.

The effects of severe renal impairment and end-stage renal disease have not been adequately established.

Liver function requires additional consideration because camizestrant exposure increases with worsening hepatic impairment. The dosing approach also differs according to which CDK4/6 inhibitor is being administered.

Drug Interactions

Camizestrant has several clinically important potential drug interactions.

Particular attention is required with:

• Medicines that prolong the QT interval

• Medicines that can cause bradycardia

• Strong CYP3A inhibitors

• Strong CYP3A inducers

• Moderate CYP3A inducers

• Certain CYP2C9 substrates

• Certain CYP2C19 substrates

The prescribing information identifies substantial potential interactions with medicines including warfarin and some proton-pump inhibitors.

Patients should provide their healthcare team with a complete list of prescription medicines, over-the-counter products, vitamins, and herbal supplements before treatment.

Evidence From the SERENA-6 Study

The accelerated U.S. approval was based on results from the SERENA-6 clinical trial.

The study included patients with estrogen receptor-positive, HER2-negative locally advanced or metastatic breast cancer who developed an ESR1 mutation while receiving an aromatase inhibitor and CDK4/6 inhibitor.

In the interim analysis, median progression-free survival was 16.0 months in the camizestrant group compared with 9.2 months in the aromatase inhibitor group.

Overall survival data were not mature at the time of the analysis, and a survival benefit had not yet been demonstrated.

The FDA's accelerated approval pathway means that continued approval may depend on confirmation of clinical benefit in subsequent evidence.

Camizestrant Compared With Other Endocrine Treatments

Camizestrant differs from aromatase inhibitors and injectable SERDs in several ways.

Aromatase inhibitors such as anastrozole and letrozole primarily reduce estrogen production. Fulvestrant acts on the estrogen receptor and is administered by intramuscular injection.

Camizestrant is an oral estrogen receptor antagonist that directly targets the receptor and is used in the approved setting when an ESR1 mutation is detected through ctDNA testing.

The available evidence does not establish camizestrant as superior to every other endocrine treatment option. The SERENA-6 trial compared the treatment strategy with continuation of the aromatase inhibitor rather than with every available alternative treatment.

Frequently Asked Questions

What is camizestrant?

Camizestrant is an oral estrogen receptor antagonist used in a specific treatment setting for HR-positive, HER2-negative locally advanced or metastatic breast cancer with an ESR1 mutation.

What is the usual dose?

The U.S. prescribing information describes a dose of 75 mg once daily, administered together with an appropriate CDK4/6 inhibitor.

Does camizestrant require ESR1 testing?

Yes. The approved U.S. indication requires detection of an ESR1 mutation using an FDA-authorized test.

Can camizestrant be taken with food?

Yes. It can be taken with or without food.

What are the important safety concerns?

Important safety considerations include QTc prolongation, cardiac arrhythmias, bradycardia, visual disturbances, laboratory abnormalities, and potential fetal harm.

Is camizestrant approved for children?

Safety and effectiveness have not been established in pediatric patients, and there is no approved pediatric indication.

Is camizestrant available in Pakistan?

The available source material does not establish current commercial availability or DRAP registration in Pakistan. This status should be independently confirmed before treatment decisions are made.

Conclusion

Camizestrant represents a newer approach to endocrine treatment for a narrowly defined group of patients with hormone receptor-positive, HER2-negative advanced breast cancer.

Its distinguishing feature is the use of ESR1 mutation detection through circulating tumor DNA to identify patients for an endocrine treatment change before radiographic disease progression.

At the same time, treatment requires careful patient selection and monitoring because of cardiac, visual, hematologic, reproductive, and drug-interaction considerations.

The information in this article is educational and should not replace the official prescribing information or individualized advice from an oncology team.

Medical Information Disclaimer

This article is provided for general educational purposes. Prescription medicines should not be started, stopped, or modified without appropriate medical evaluation. Treatment decisions depend on the individual's cancer characteristics, biomarker results, previous treatments, other medicines, organ function, and overall clinical circumstances.

For complete prescribing information, healthcare professionals should consult the current regulatory labeling and applicable local guidance.