Anastrozole is an aromatase inhibitor approved by the U.S. Food and Drug Administration (FDA) to treat:

  • postmenopausal women diagnosed with hormone-receptor-positive, early-stage breast cancer after surgery (or possibly chemotherapy and radiation) to reduce the risk of the cancer coming back
  • postmenopausal women diagnosed with advanced-stage or metastatic hormone-receptor-positive breast cancer 

Anastrozole won’t work on hormone-receptor-negative breast cancer. Anastrozole shouldn’t be taken at the same time as tamoxifen.

Image result for anastrozole and breast cancer

Anastrozole is a pill taken once a day. Most doctors recommend taking Anastrozole at the same time each day.

You should not take Anastrozole if you are breastfeeding, pregnant, trying to get pregnant, or if there is any chance that you could be pregnant. Anastrozole may cause damage to developing embryos. You should use an effective non-hormonal type of birth control — such as condoms, a diaphragm along with spermicide, or a non-hormonal I.U.D. – while you are taking Anastrozole. Ask your doctor which type of non-hormonal birth control would be best for you, as well as how long you should use this type of birth control after you stop taking Anastrozole.

Benefits of Anastrozole

The large ATAC (Anastrozole, Tamoxifen Alone or in Combination) trial compared Anastrozole to tamoxifen after surgery. The researchers wanted to know how the medicines worked by themselves as well as together to see which combination would be the best treatment for postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer. Based on the results of this trial, giving Anastrozole and tamoxifen at the same time isn’t recommended.

Image result for anastrozole and breast cancer

The ATAC study found that 5 years of Anastrozole is better than 5 years of tamoxifen as the first hormonal therapy for postmenopausal women with early-stage, hormone-receptor-positive breast cancer. Anastrozole is better than tamoxifen for:

  • increasing the time before the cancer comes back in those who experience recurrence
  • reducing the risk of the cancer spreading to other parts of the body
  • reducing the risk of a new cancer developing in the other breast

Research presented at the 2013 San Antonio Breast Cancer Symposium showed that Anastrozole can lower the risk of first-time, hormone-receptor-positive breast cancer in postmenopausal women at high risk who haven’t been diagnosed. Anastrozole isn’t approved by the FDA for this use, but doctors may consider it a good alternative to other hormonal therapies approved to reduce risk in high-risk women.

It’s possible that the FDA may approve Anastrozole to be used to reduce risk in high-risk postmenopausal women who haven’t been diagnosed.

How Anastrozole Is Given:

  • Anastrozole is a pill, taken by mouth.
  • You should take anastrozole at about the same time each day.
  • You may take anastrozole with or without food.
  • If you miss a dose of anastrozole, take it as soon as you remember unless it is almost time for the next dose. Do not take a double dose to make up a missed dose.
  • You should not stop taking anastozole without discussing with your physician, even if you feel well.

The amount of anastrozole that you will receive depends on many factors, including your general health or other health problems, and the type of cancer or condition being treated. Your doctor will determine your dose and how long you will be taking anastrozole.

Side effects of Anastrozole

Because Anastrozole lowers the amount of estrogen in the body, less estrogen reaches bone cells, which can lead to bone thinning and weakening and a higher-than-average risk of broken bones. This side effect can be very troubling for some women. If you have osteoporosis, your doctor may recommend that you take tamoxifen rather than Anastrozole because of this possible side effect.

The ATAC results reported in 2007 showed a finding that hadn’t been seen before. The higher risk of broken bones associated with Anastrozole disappeared after the women stopped taking Anastrozole. The researchers will see if this result continues as more data is collected and analyzed.

Image result for anastrozole side effects

Other common side effects of Anastrozole are:

  • bone and joint pain
  • nausea
  • vomiting
  • hot flashes
  • weakness
  • fatigue

Some women may have other side effects while taking Anastrozole:

  • headache
  • loss of appetite
  • constipation
  • diarrhea
  • heartburn
  • weight gain
  • mood changes
  • difficulty sleeping
  • dizziness
  • vaginal bleeding
  • vaginal dryness
  • dry mouth
  • dry skin
  • cough
  • hair changes

Some side effects may mean that you’re having an allergic reaction to Anastrozole. If you have any of the following symptoms, call your doctor immediately:

  • chest pain
  • blurred vision
  • racing heartbeat
  • rash or hives
  • swelling of the eyes, face, lips, tongue, throat, arms, hands, feet, ankles, or lower legs
  • breast pain or new lumps in the breast

When To Contact Your Doctor or Health Care Provider:

Contact your health care provider immediately, day or night and go to the nearest emergency room, if you should experience any of the following symptoms:

  • New or worsening chest pain
  • Shortness of breath
  • Swelling of the face, lips, tongue and/or throat
  • Difficulty swallowing and/or breathing.

The following symptoms require medical attention, but are not emergency situations. Contact your health care provider within 24 hours of noticing any of the following:

  • Vaginal bleeding (similar to a period)
  • Tickling, Tingling, or Numbness of your skin
  • Nausea (interfering with ability to eat and unrelieved with prescribed medication)
  • Vomiting (vomiting more than 4-5 times in a 24 hour period)
  • Yellowing of your skin or the whites of your eyes
  • Pain on the right side of your stomach-area

Always inform your health care provider if you experience any unusual symptoms.


  • Before starting anastrozole treatment, make sure you tell your doctor about any other medications you are taking (including over-the-counter drugs, vitamins, or herbal remedies)
  • Anastrozole interacts with certain medications. Make sure you tell your doctor if you are taking these medications:
    • Tamoxifen
    • Estrogen
    • Warfarin
    • Estrogen/estradiol-containing medications (commonly used for menopause and birth-control)
  • Before starting anastrozole treatment, make sure you tell your doctor about health conditions you have including: heart conditions, osteoporosis, and abnormal cholesterol. Anastrozole may cause increased risk for heart disease. Talk with your healthcare provider to weigh the benefit and risks.
  • Inform your health care professional if you have not had menopause yet (premenopausal).
  • Inform your health care professional if you are pregnant or may be pregnant prior to starting this treatment. Anastrozole is pregnancy category X (anastrozole may be hazardous to the fetus. Anastrozole is contraindicted in women who are pregnant or may become pregnant).
  • Anastrozole may enter breast milk. It is unclear what effect this may have on babies. Tell your doctor if you are breastfeeding or plan to breastfeed.

Self-Care Tips:

  • If you experience hot flashes, wearing light clothing, staying in a cool environment, and putting cool cloths on your head may reduce symptoms. Consult your health care provider if these worsen, or become intolerable.
  • Acetaminophen or ibuprofen may help relieve discomfort from generalized aches and pains. However, be sure to talk with your doctor before taking it.
  • Anastrozole causes little nausea. However, to reduce nausea, take anti-nausea medications as prescribed by your doctor before taking it.
  • Good health practices such as getting plenty of rest and eating a healthy diet along with regular exercise are recommended
  • If you experience symptoms or side effects, be sure to discuss them with your health care team. They can prescribe medications and/or offer other suggestions that are effective in managing such problems.

Monitoring and Testing While Taking Anastrozole:

You will be checked regularly by your doctor while you are taking anastrozole, to monitor side effects and check your response to therapy. No additional blood work or tests are required for anastrozole.

How Anastrozole Works:

Hormones are chemical substances that are produced by glands in the body, which enter the bloodstream and can cause effects in other parts of the body. For example, the hormone testosterone is made in the testicles and is responsible for male characteristics such as deepening voice and increased body hair. The use of hormone therapy to treat cancer is based on the observation that cancer cell growth can partially depend on hormone binding to receptors on the cancer cell surface.

Hormone therapies can work through methods such as stopping the production of a certain hormone or interfering with hormone binding to the cancer cell receptor. The different types of hormone therapies are categorized by their function and/or the type of hormone that is affected.

Anastrozole is an aromatase inhibitor. This means it blocks the enzyme aromatase (found in the body’s muscle, skin, breast and fat), which is used to convert androgens (hormones produced by the adrenal glands) into estrogens. Tumor cells dependent on estrogens grow less when there is no estrogen.

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