Understanding Hormone Therapy for Breast Cancer

Breast cancer is the most common cancer among women worldwide. If you or a loved one has been diagnosed with hormone receptor-positive breast cancer, your doctor may bring up something called “hormone therapy.” This term can sound frighteningly vague if you don’t understand what it means.

What exactly is hormone therapy?

  • Hormone therapy is a treatment approach that works by blocking or lowering the levels of estrogen and other hormones that can fuel breast cancer growth.
  • It’s used for breast cancers that tests show are estrogen receptor-positive (ER+) and/or progesterone receptor-positive (PR+). This means the cancer cells have receptors that allow estrogen and progesterone to attach to them and stimulate their growth.
  • By blocking these hormone receptors or reducing hormone levels, the goal is to slow or stop cancer cell proliferation.

How do hormone therapy drugs work?

There are a few main types of hormone therapy medications:


  • Tamoxifen works by attaching to estrogen receptors on cancer cells so that real estrogen can’t bind to them. This starves the cells of the hormone input they need to proliferate.
  • It’s taken as an oral pill, usually daily.

Aromatase inhibitors

  • Aromatase inhibitors (AIs) work by blocking an enzyme called aromatase, which the body uses to produce estrogen. This causes overall estrogen levels to fall.
  • Common AIs are anastrozole, letrozole and exemestane. They are also taken as oral tablets.

Ovarian suppressors

  • Goserelin and leuprolide suppress estrogen production by the ovaries. They do this by telling the pituitary gland in the brain to stop stimulating ovarian activity.
  • These drugs require an injection under the skin, such as in the stomach area. The injection is given once a month or once every three months.


  • Fulvestrant works by binding to estrogen receptors on cells and downregulating them. This makes it harder for estrogen to exert its effects on any remaining receptors.
  • It’s given monthly by injection into the buttocks.

When is hormone therapy used?

There are a few main settings when hormone therapy is prescribed:

  • After surgery – For early stage cancers with successful lumpectomy or mastectomy, hormone therapy is typically used as adjuvant therapy for 5-10 years. This helps eradicate any remaining stray cancer cells and reduce recurrence risk.
  • Before surgery – Neoadjuvant hormone therapy may shrink large tumors to make them easier to operate on. Results determine if surgery is still needed.
  • For metastatic cancer – Hormone therapy is a good initial treatment for ER+ cancer that has already spread beyond the breast to other body areas. It may keep metastases under control for several years.
  • To prevent cancer – For women at high risk but with no cancer yet, drugs like tamoxifen and AIs can be used preventatively to reduce the chance of developing breast cancer.

What are the potential side effects?

The most common side effects mimic menopausal symptoms like:

  • Hot flashes
  • Night sweats that soak bedding
  • Vaginal dryness and painful intercourse
  • Mood changes like irritability
  • Joint pain and muscle ache

Unlike natural menopause, medication-induced menopause involves rapidly plummeting estrogen. This shock to the system makes side effects more intense in some women. They also depend on the type and dose of hormone drug.

Tips for coping with side effects:

  • Keep bedroom cool at night
  • Dress in breathable cotton layers
  • Use vaginal moisturizers and lubricants
  • Exercise gently to reduce joint pain
  • Communicate openly with your care team

The good news is side effects often improve over time as the body adjusts. Some women have very minimal symptoms, while others struggle with coping. Work closely with your doctor to fine-tune your hormone drug regimen.

What happens if hormone therapy stops working?

While hormone therapy buys precious time by holding cancer at bay, unfortunately, there is still a risk cancer cells mutate so they learn to live and grow with low estrogen. This is called hormone resistance. Warning signs are:

  • Detection of new tumors or growths
  • Rising blood tumor marker levels
  • Increase in size/number of metastases

If this happens, your oncologist will likely prescribe a different hormone drug that works in alternative ways. Or they may recommend adding other treatments like targeted therapy or chemotherapy. The goal is to retain control of cancer cell spread for as long as possible.

Does taking hormone therapy for years pose other risks?

Long-term hormone therapy lasting up to 10 years does not appear to increase the risk of other health conditions. However, using tamoxifen for more than 5 years slightly elevates the chance of developing uterine cancer. So doctors may recommend a hysterectomy after several years if you still have a uterus.

The benefits of hormone therapy continue even after stopping. Protection against breast cancer recurrence persists for years after the 5-10 year mark.

When are hormone drugs used preventatively?

For those with no cancer yet but at high inherited risk, drugs like tamoxifen and AIs may be used to reduce odds of developing breast cancer. Starting at age 35, five years of preventative hormone treatment cuts relative risk by 50 percent. Side effects are similar to those already explained.

Doctors also prescribe hormone therapy alongside other treatments like chemo and radiation in some cases.

The takeaway

In essence, hormone therapy for breast cancer revolves around blocking estrogen signaling and output using various drugs. This approach is highly effective for ER+ cancers. Like most cancer treatments, hormone medications have downsides like menopausal side effects. But they do allow many women with this subtype of breast cancer to enjoy years of quality life. Discussing expectations, side effect coping methods and monitoring with your oncologist is key. Together you can determine the ideal hormone treatment plan and duration.

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