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How endocrine therapy for cancer works

Doctor and patient discussing together on a couch.
Certain cancers—like breast cancer—are deeply affected by hormones. In order to stop cancer growth from occurring or to at least slow it down, there are treatments that exist that can alter or block the hormones. This type of treatment is most commonly referred to as hormone therapy or endocrine therapy (sometimes also referred to as hormonal therapy). For the sake of lowering confusion throughout this blog post, we’re going to move forward using the term endocrine therapy. 

Keep reading for a breakdown of what endocrine therapy for breast cancer (and all cancers) is, how it works, and when breast cancer patients may encounter it. 

Endocrine Therapy Definition

Endocrine therapy is classified as a systemic treatment. It involves targeted hormones that circulate in the body. The endocrine therapy drugs used in the course of treatment travel throughout the body in order to find hormones and target them—which means this type of treatment can affect the entire body unlike radiation or surgery which are targeted therapies. This type of treatment only becomes localized if surgery is used to remove hormone-making organs.

Endocrine therapy can stop the body from creating the hormone that causes cancer growth or can block the hormone from attaching to cancer cells. This type of therapy can also alter the hormone so it doesn’t work like it’s supposed to and can lessen some cancer symptoms. 

These are some examples of endocrine therapy used to treat breast cancer:
  • Aromatase inhibitors (AIs). Such as anastrozole, exemestane, and letrozole.
  • Selective estrogen receptor modulators (SERMs). Such as tamoxifen and raloxifene.
  • Estrogen receptor antagonists. Such as fulvestrant and toremifene.
  • Luteinizing hormone-releasing hormone (LHRH). Such as agonists, such as goserelin, leuprolide, and triptorelin.
  • Oophorectomy. This is a form of surgery that removes ovaries.

When endocrine therapy occurs

There are a few different times when a breast cancer patient may encounter endocrine therapy for cancer treatment. 

  • Post-surgery. Usually, endocrine therapy occurs after surgery if surgery is deemed a necessary part of treatment to reduce the risk of the breast cancer returning or a new breast cancer developing. 
  • During or after radiotherapy or surgery. Endocrine therapy may occur if the patient is having radiotherapy or chemotherapy after surgery. Patients can start endocrine therapy during or after radiotherapy, but if they’re doing chemotherapy it’s most likely to start afterwards.
  • Before surgery. In some cases, endocrine therapy may be given before surgery to reduce the size of the cancer.
  • In replacement of surgery. If surgery isn’t an option for a patient, they may experience endocrine therapy in replacement for surgery. 

Getting endocrine therapy

There are a few types of ways that endocrine therapy can be administered to patients. 

  • Oral drugs. Similar to other medicines, endocrine therapy medicines can be taken via pill, capsule, or liquid at home. How often the patient needs to take these drugs varies based on their unique type of cancer and the drug they’re taking. Patients need to follow physician instructions exactly and need to pay close attention to any special precautions they need to take. 
  • Injectable drugs. When endocrine therapy is delivered via injections, this is done in the leg, hip, or arm and is known as an intramuscular (or IM) injection. In some cases, the injections are given just under the skin of the abdomen which is known as a subcutaneous (SC or sub-Q) injection. While some patients learn how to do their own injections at home or have a caregiver do them, it’s very common to receive these injections in a doctor’s office or treatment center. 
  • Surgery to remove hormone-making organs. As briefly noted above, some patients will undergo surgery to remove an organ that creates hormones. For women with breast cancer, they may have surgery to remove their ovaries (oophorectomy) as this is the body’s main source of estrogen and progesterone.

Your doctor and care team will help you determine if endocrine therapy is the right course of treatment for you. Learn more about your treatment options by using Outcomes4Me!

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