Tamoxifen (Soltamox) is a well-known hormonal therapy used to lower the chance of breast cancer recurring (coming back after treatment). For nearly 50 years, doctors have prescribed tamoxifen for people with hormone receptor (HR)-positive breast cancer — a type of cancer that uses estrogen or progesterone to grow.

Hormonal therapy like tamoxifen can reduce the risk of recurrence by up to 50 percent. However, taking tamoxifen every day for five to 10 years can be hard. Side effects such as hot flashes, tiredness, headaches, anxiety, and vaginal dryness can make it difficult to stick with the treatment plan.

If the side effects are hard to manage, you might be thinking about taking a break from tamoxifen or stopping treatment altogether. However, not taking your hormonal therapy as prescribed increases your risk of recurrence, metastasis (cancer spread), and even cancer-related death.

Keep reading to learn more about the risks of stopping tamoxifen. This can help you have an informed discussion with your cancer care team about your options.

What Are the Odds of Breast Cancer Recurrence?

The risk of breast cancer recurrence is different for everyone. A 2021 study found that breast cancer returned within five years in about 1 in 6 people with HR-positive breast cancer that had spread to the lymph nodes.

Your cancer care team will look at several factors to estimate your personal risk of recurrence and recommend treatment options to lower that risk. These factors include:

• The type of breast cancer cells
• The molecular subtype (such as hormone receptor-positive or HER2-positive)
• The stage of the cancer (based on tumor size, lymph node involvement, and whether it has spread)
• Your age

You can also ask about genomic testing, which looks for specific genes in the cancer cells. The test results can help you learn more about your individual risk of recurrence and which breast cancer treatments may work best for you.

When Does Breast Cancer Usually Come Back?

At least 50 percent of breast cancer recurrences happen within five years of the first diagnosis. Some people, especially those with estrogen receptor (ER)-positive breast cancer, face a higher risk of breast cancer returning at least 10 years after finishing treatment. This is called late recurrence.

A 2021 study, published in the Journal of the National Cancer Institute, followed more than 36,000 women with breast cancer and found that recurrence could occur up to 32 years after the original diagnosis. Risk factors for late recurrence included:

• Lymph node involvement
• Large tumor size
• ER-positive breast cancer

Hormonal therapies like tamoxifen can help reduce the risk of late recurrence.

How Does Tamoxifen Prevent Breast Cancer Recurrence?

Tamoxifen is a type of hormonal therapy (also known as endocrine therapy) called a selective estrogen receptor modulator (SERM). It works by blocking the hormone estrogen from attaching to breast cancer cells.

In HR-positive breast cancer, estrogen helps cancer cells grow. Tamoxifen attaches to the cells’ estrogen receptors so that estrogen can’t bind there. This stops estrogen from fueling the tumor’s growth.

Your cancer care team may recommend tamoxifen after surgery and radiation if you have hormone receptor-positive breast cancer. Tamoxifen usually doesn’t work for HR-negative breast cancer, which doesn’t use estrogen to grow.

Tamoxifen is often the first-choice hormonal treatment for women who haven’t gone through menopause, but it’s also prescribed to postmenopausal women and to men with breast cancer, according to Breastcancer.org.

Breast cancer survivors are often advised to take tamoxifen for at least five years to reduce the risk of recurrence. If you have early-stage breast cancer, you may be able to stop after five to 10 years or switch to a different hormonal therapy. If you have advanced breast cancer, your doctor may recommend staying on tamoxifen as long as the benefits outweigh the side effects.

Why Don’t Some People Take Tamoxifen as Prescribed?

Up to 3 out of 4 people prescribed hormonal therapy for breast cancer don’t take it as instructed. They may skip doses, stop taking it early, or never start at all.

One of the main reasons people don’t take tamoxifen as prescribed is because of side effects. Although tamoxifen helps reduce the risk of recurrence by blocking estrogen in the breast, it also blocks the hormone in other parts of the body, which can cause:

• Hot flashes
• Night sweats
• Joint pain
• Fatigue (extreme tiredness that may not improve with rest)
• Vaginal dryness
• Mood changes
• Weight gain
• Depression or anxiety

• Osteopenia (low bone density)

Tamoxifen may also raise the risk of certain other health issues. Your doctor may recommend stopping treatment if you develop one of these medical conditions:

• Endometrial cancer (uterine cancer)
• Blood clots
• Stroke
• Cataracts
• Osteoporosis (bone loss)
• Liver problems

If tamoxifen side effects affect your quality of life or lead to another condition, the drug’s risks may outweigh the benefits. Don’t stop taking tamoxifen on your own, however. Talk with your cancer care team about whether you should continue, pause, or switch to a different treatment.

Will Your Cancer Return if You Don’t Take Tamoxifen?

There’s no way to know for sure whether your cancer will come back if you don’t take tamoxifen as recommended. However, research shows that stopping tamoxifen early or not taking it as prescribed increases the risk of recurrence and death related to breast cancer. A 2016 study in the Journal of Clinical Oncology found that postmenopausal women who stopped hormonal treatment early had a 35 percent to 56 percent higher risk of recurrence.

Other cancer research has shown that taking tamoxifen significantly reduced recurrence risk in people with hormone receptor-positive breast cancer. A 2021 study in the journal Clinical Cancer Research looked at the link between stopping hormonal therapy early and breast cancer recurrence in premenopausal women. The researchers found that recurrence occurred in 20 percent of participants who quit early but just 11 percent of those who completed their full course. This means stopping treatment early nearly doubled recurrence risk.

Talk to Your Cancer Care Team Before Stopping Tamoxifen

If you’re thinking about stopping tamoxifen or taking a break, it’s important to talk with your cancer care team first. They may be able to recommend ways to make side effects more manageable, such as:

• Talk therapy
• Breathing exercises
• Acupuncture
• Yoga

These complementary therapies may help ease hot flashes, joint and bone pain, anxiety, or depression. Some people find that side effects like hot flashes also get better with time.

Your healthcare provider may also suggest adjusting your dose of tamoxifen or switching to a different hormonal therapy. For example, aromatase inhibitors, which are often prescribed after menopause, lower the amount of estrogen the body produces. These medications can also cause side effects like hot flashes and vaginal dryness, but some people find them easier to tolerate than tamoxifen.

Your cancer care team can also help you build healthy habits that support your well-being and lower your risk of recurrence. These steps may include:

• Getting regular physical activity
• Eating a balanced, nutritious diet
• Limiting alcohol

If you’re feeling overwhelmed or unsure about tamoxifen, you’re not alone — and you don’t have to make this decision alone either. Your care team is there to help you weigh the risks and benefits and choose the best next step for you.

Find Your Team

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Have you had trouble sticking with tamoxifen due to side effects or other health conditions? Did you discuss these challenges with your cancer care team? Share your experience in the comments below, or start a conversation by posting on your Activities page.