What Is Endocrine Therapy?
Endocrine therapy is one of the main treatments for hormone receptor-positive (HR+) breast cancer. That’s cancer that uses the sex hormones estrogen, progesterone, or both to grow.
Endocrine therapy, also called hormone therapy, can either lower the amount of hormones your body makes or keep the cancer cells from using those hormones. It’s most often prescribed for at least 5 years to help keep cancer from coming back after surgery.
Most everyone whose cancer is HR+ is offered endocrine therapy. It may be combined with other types of treatment, like chemotherapy or targeted therapy. Which specific drug you’ll get depends on things like the stage of the cancer and whether you’ve been through menopause.
How Does Endocrine Therapy Work?
Selective estrogen receptor modulators (SERMs). These drugs attach to the hormone receptors on breast cancer cells, blocking estrogen or progesterone from doing the same. In other parts of your body, they act like estrogen and can have both protective and harmful effects.
Aromatase inhibitors. While your ovaries are the main source of estrogen in your body before you go through menopause, an enzyme called aromatase causes fat cells and other tissues to make it too. Aromatase inhibitors block that action.
Selective estrogen receptor degraders (SERDs). Like SERMs, these drugs block hormone receptors on breast cancer cells. But they also destroy those receptors. And unlike SERMs, they don’t mimic the action of estrogen in other tissues.
Luteinizing hormone-releasing hormone (LHRH) agonists. These drugs stop your body from making hormones that signal your ovaries to produce estrogen. When your treatment is finished, your body can go back to making estrogen.
It’s less common, but doctors can prescribe medications to treat HR+ breast cancer that act like estrogen, testosterone, or progesterone. These include ethinyl estradiol, fluoxymesterone, and megestrol acetate.
Which Endocrine Therapy Medications Are Used for HR+ Breast Cancer?
Endocrine therapy – also called hormone therapy – involves several classes of drugs that work differently to fight HR+ breast cancer. It can be used to treat any stage of HR+/HER2- breast cancer. Your treatment may involve more than one type of drug. Medications that are used to treat HR+ breast cancer include:
When Is Endocrine Therapy Prescribed for HR+ Breast Cancer?
Endocrine therapy is only prescribed for people whose tumor cells test positive for hormone receptors. It can treat any stage of cancer, although you’ll have a different choice of drugs for early-stage vs. advanced cancer. Also, some drugs are only used after you’ve gone through menopause.
Endocrine therapy can be used in four ways:
After surgery (adjuvant therapy). The main reason people get endocrine therapy is to try to keep HR+ breast cancer from coming back after surgery.
Before surgery (neoadjuvant therapy). For stage II or stage III cancer, endocrine therapy may be used to shrink a tumor before surgery to make it easier to remove.
Extending survival. Endocrine therapy can help you live longer with HR+ breast cancer that has spread to other parts of your body, or has come back after treatment.
Preventive therapy. If you’re at high risk of breast cancer – for example, because of certain gene mutations or precancerous conditions – you may get endocrine therapy to try to keep you from ever getting cancer.
There are many treatment plans involving endocrine therapy. Your doctor will recommend a treatment plan that’s tailored to your individual situation. But cancer experts have general guidelines for when to use specific drugs.
For early-stage HR+ breast cancer, doctors typically prescribe endocrine therapy for 5-10 years. Before menopause, tamoxifen is usually recommended. If you can’t take it for some reason, an aromatase inhibitor plus an LHRH may be best. Women who go through menopause during treatment may switch from tamoxifen to an aromatase inhibitor.
After menopause, you may be given either tamoxifen or an aromatase inhibitor. Another option is to take one of these drugs for several years, and the other for several more.
For stage IV (metastatic) HR+ breast cancer, endocrine therapy is used for as long as it’s helpful. The first-line recommended treatment is either an aromatase inhibitor or fulvestrant, plus a targeted therapy drug called a CDK4/6 inhibitor. If you haven’t been through menopause, you’ll also need some form of ovarian suppression with these drugs. People past menopause could get toremifene. Tamoxifen is another option for anyone.
If you have advanced cancer and the tumor cells have a mutation in the ESR1 gene, you might try elacestrant if another endocrine therapy drug hasn’t worked.
How Effective Is Endocrine Therapy?
Clinical trial studies show the effectiveness of endocrine therapy itself and in combination with other drugs:
What Are the Common Side Effects of Endocrine Therapy?
The different types of endocrine therapy can cause different side effects, but the most common are similar to what you might have during menopause. In fact, ovarian suppression does put you into menopause.
Many people are very bothered by these side effects, to the point that as many as half of those prescribed endocrine therapy don’t stick with it for the full 5 years.
Less common side effects of tamoxifen include blood clots and cataracts. It can also raise your risk of endometrial and uterine cancer if you’ve gone through menopause.
Talk to your doctor about how to manage these side effects. They might be able to change your dose, switch you to a different drug, or give you another medication to help.
If you’re taking an aromatase inhibitor, you should have regular bone mineral density scans and may need to take bone-strengthening medication.
Who Should Not Take Endocrine Therapy?
If you have breast cancer that’s hormone receptor negative, (HR-) that means tumor cells don’t use sex hormones to grow, and endocrine therapy won’t help you. You also shouldn’t take endocrine therapy drugs if you’re pregnant or breastfeeding.
If you don’t have breast cancer but are trying to reduce your risk, you shouldn’t take tamoxifen If you have a history of blood clots.
How Much Does Endocrine Therapy Cost?
Many common medications used in endocrine therapy have been on the market for many years, so you can get them in generic versions, which are typically less expensive than name brands. Exactly what you’ll pay for a particular drug depends on your insurance coverage.
Without insurance, you may be able to get tamoxifen for as little as $20-$50 a month, or an aromatase inhibitor from around $100. SERDs are more expensive, with fulvestrant costing about $2,700 for a monthly shot.
Many drug companies have programs to help lower your out-of-pocket costs. There are also charitable organizations that can help you pay for prescription drugs, such as the Patient Access Network Foundation.
Clinical Trials for HR+ Breast Cancer
Doctors are always looking for better ways to treat HR+ breast cancer, and clinical trials are an important part of that process. They’re how researchers test the safety and effectiveness of both new drugs and different ways to use existing drugs.
For example, studies going on now are trying to learn whether endocrine therapy works better for certain people when combined with other kinds of drugs, like chemotherapy and targeted therapy. Researchers are also working to determine what’s the best length of time for endocrine therapy.
You can help doctors learn more and possibly get access to cutting-edge treatment by taking part in a clinical trial. Ask your doctor whether a clinical trial might be right for you and if they know of one in your area.
Is Endocrine Therapy Right for Me?
If you have HR+ breast cancer, you’ll likely be offered endocrine therapy. Your doctor can help you decide whether it’s the best choice for you, and which drug or combination of drugs may be most helpful. There are number of things to consider:
Whether you’re still ovulating. Some endocrine therapy drugs work best if you’re past menopause. If you aren’t, you might need to take more drugs or have surgery to keep your ovaries from making estrogen. But that could mean you aren’t able to get pregnant in the future. Ask your doctor about options that may preserve your fertility.
The stage of the cancer. Endocrine therapy is a treatment option for all stages of HR+ breast cancer. But certain drugs are only approved to treat cancer that has spread to other parts of your body.
How well you can manage the side effects. Many people find that the side effects of endocrine therapy, which tend to be similar to menopause symptoms, are hard to tolerate, especially over 5-10 years of treatment. Ask your doctor what to expect and what you can do to make treatment easier.
Cost. You should discuss your doctor’s recommendations with your insurance company so you know what out-of-pocket costs you can expect. Many endocrine therapy drugs come in generic versions that can be much less expensive than brand names. If you don’t have insurance, you may be able to get help from a drug company’s patient assistance program or a charitable organization.