Tamoxifen is a selective estrogen receptor modulator (SERM) that doctors prescribe for breast cancer treatment. They may also recommend it to those with ovarian tumors. It can cause side effects such as blood clots, hot flashes, and constipation, and it may interact with other medications.

According to the Centers for Disease Control and Prevention (CDC), 19,571 new cases of ovarian cancer and 13,445 deaths of women from this cancer occurred in the United States in 2019.

Ovarian cancer affects the ovaries, which are reproductive organs that people assigned female at birth typically have. This type of cancer may involve epithelial, germ cell, or stromal tumors. Malignant tumors can metastasize, or spread beyond the ovaries.

Hormone therapy, such as tamoxifen, involves using hormone-blocking drugs to treat ovarian cancer. Tamoxifen works by blocking the activity of a hormone called estrogen.

Read on to learn more about the role of tamoxifen in ovarian cancer treatment, including potential side effects and risks that a person should consider.

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Tamoxifen is a drug that doctors prescribe to people who have breast cancer. “Nolvadex” and “Soltamox” are other names for this drug.

A doctor may recommend tamoxifen for the following reasons:

  • as an additional treatment for people with breast cancer who have undergone surgery or radiation
  • to reduce the risk of invasive breast cancer in females with ductal carcinoma in situ, or noninvasive breast cancer
  • to reduce the risk of breast cancer in people with high risk for the condition, such as those with genetic conditions or family histories that their doctors have identified as high risk

Tamoxifen has many off-label uses — meaning that the Food and Drug Administration (FDA) has not approved it for these uses. Doctors may use it to treat other cancers.

The American Cancer Society (ACS) states that tamoxifen may also help treat ovarian stromal tumors. Stromal tumors start within the structural tissue cells of the ovaries and produce hormones called estrogen and progesterone. Tamoxifen is not a treatment for epithelial ovarian cancers.

Learn more about ovarian cancer here.

How does the drug work?

Tamoxifen is effective only in cancer cells that have hormone-positive receptors.

It acts as an anti-estrogen drug, blocking the effects of the estrogen.

The drug occupies the receptor on a cancer cell, preventing estrogen from attaching to the cell. This means the cell will not receive signals from the estrogen. Estrogen may encourage cancer cells to grow, so blocking this action will stop them from growing and multiplying.

Tamoxifen can exert complex hormonal actions. While it can act as an anti-estrogenic drug, it can also have some estrogenic effects and promote the hormone’s release in certain organs. This is why it is a SERM.

Hormone therapy is a common treatment method for recurrent ovarian cancer when other treatments have failed or when additional chemotherapy is not an option.

Tamoxifen may be a favorable therapy in comparison to other treatments types because:

  • a person can take it orally
  • it has tolerable side effects
  • it has an overall lower cost

A 2017 study assessing the effectiveness of chemotherapy and tamoxifen in platinum-resistant ovarian cancer showed that tamoxifen can affect a person’s quality of life. “Platinum-resistant cancer” means that the cancer has come back within 6 months after treatment begins.

The results showed that people receiving chemotherapy had longer median progression-free survival — meaning that the disease did not worsen during or after therapy — than people taking tamoxifen. Specifically, people receiving chemotherapy had 12.7 weeks of progression-free survival compared to 8.3 weeks for people on tamoxifen. However, people receiving chemotherapy experienced poorer quality of life.

Another 2017 study found that either tamoxifen or another drug, called letrozole, can be a rational treatment option for people with estrogen-positive high grade ovarian cancer.

Learn more about other treatments available for people with ovarian cancer here.

Dose of tamoxifen for ovarian cancer

Tamoxifen is available in both a pill and a liquid form.

In most cases, a person has to take 20 milligrams per day at the same time. Those who have lactose intolerance should ask their doctor if the treatment is safe for them, as tamoxifen may contain small traces of lactose.

A person should also avoid stopping treatment without their doctor’s advice.

Research has shown that tamoxifen can increase the risk of ovarian cysts in premenopausal and postmenopausal women who receive tamoxifen therapy for breast cancer.

An older study from 2005, in which 150 participants were treated with tamoxifen, found that 49.1% of the premenopausal and 1.1% of the postmenopausal women developed ovarian cysts. Moreover, chemotherapy did not have any effect on the cysts.

Researchers do not yet know exactly how cysts may develop.

People who take tamoxifen may experience some side effects. The anti-estrogen activity of tamoxifen can cause hot flashes and vaginal dryness.

Other side effects that people may experience include:

Tamoxifen can cause serious side effects such as:

People should seek medical attention if they are experiencing vision problems or swelling, pain, or redness in their calf.

Additionally, a 2017 study of 397 women with breast cancer found that those who had taken tamoxifen were less likely to give birth to a child after diagnosis than those who had not taken the drug.

Drug interactions

Research notes that tamoxifen can interact with other drugs. People should avoid the following medications while on tamoxifen because they can interfere with tamoxifen’s activity:

  • antidepressants, such as paroxetine, fluoxetine, and duloxetine
  • neuroleptic drugs, such as pimozide and thioridazine
  • heart medications, such as quindine and ticlopidine
  • medications to treat infection, such as terbinafine
  • other medications, such as cinacalcet and conivaptan

The researchers recommend that doctors consider temporarily halting tamoxifen treatment before a person undergoes a surgical procedure. This is because taking tamoxifen while undergoing surgery may increase the chance of developing deep vein thromboembolism. The individual may resume taking tamoxifen 2 weeks after the surgery.

Doctors may advise people on when to take or not take certain medications while they are using tamoxifen.

Tamoxifen is a SERM drug. According to the ACS, medications of this type can increase the risk of endometrial cancer and uterine sarcoma in people who have gone through menopause. People might experience unusual vaginal bleeding, in which case they should seek medical attention.

Long-term tamoxifen therapy can increase a person’s risk of developing uterine cancer. However, treatment can be successful if they receive an early diagnosis.

Learn more about endometrial cancer here.

Tamoxifen is a breast cancer treatment drug that people may also take if they have ovarian tumors. It blocks estrogen activity and therefore slows or stops cancer cell growth.

However, people who receive tamoxifen therapy may develop blood clots, so doctors may recommend other cancer medications.

Additionally, tamoxifen may not be safe for people who take certain prescription medications, as these may reduce tamoxifen’s effectiveness.