Treatment & Side-Effects

Anti-estrogen treatment and side effects.

If you were diagnosed with estrogen receptor positive (ER+), also known as hormone receptor positive, early stage breast cancer, your doctor may have prescribed you something called anti-estrogen therapy (also called hormonal therapy, hormone treatment, or endocrine therapy). But what is it? How does it work? How long do you need to take it? And are there side effects?

Why does estrogen matter for some breast cancer patients?

If your tumor cells contain estrogen receptors, then your breast cancer is considered estrogen receptor-positive (ER+).

The majority of estrogen in a woman’s body is produced by the ovaries, while the rest is produced by other organs throughout the body (e.g. bone, breast, fat tissues, etc.).

You can imagine estrogen receptors as the “lock” on cancer cells and estrogen is the “key”. When estrogen attaches to these receptors, it will “unlock” a signal which causes the cancer to multiply and potentially spread to other parts of the body.

To prevent the cancer from multiplying, physicians often prescribe something called anti-estrogen therapy.

What is anti-estrogen treatment / hormonal therapy?

Anti-estrogen treatments are medications to treat ER+ breast cancer. Two of the most common anti-estrogen therapies used to treat ER+ breast cancer are Aromatase Inhibitors and Tamoxifen. Which one your doctor prescribes will depend on your specific tumor, menopausal status, and other factors.

Reducing the amount of estrogen or blocking its signaling can help lower your risk of ER+ breast cancer coming back.

How long will you need to be on anti-estrogen therapy?

Because estrogen receptor-positive breast cancer is not a 5 year disease, and there is a risk of the cancer returning, recent studies recommend continuing therapy for a full 10 years to help reduce that risk in some women. However, according to 4 major studies, out of 100 patients, only about 3-5 actually benefit from continuing anti-estrogen therapy beyond 5 years (years 5 to 10).

In addition, there are also significant side effects reported to be associated with anti-estrogen therapy.

What are the potential side effects?

Although an additional 5 years of anti-estrogen therapy may help some women lower their risk of the cancer returning, anti-estrogen therapy is also known to be associated with multiple side effects that can impact quality of life, as well as safety issues, some of which may be serious.8,9

Potential Side Effects Aromatase Inhibitors Tamoxifen
Long-term safety concerns
Endometrial cancer pink checkmark
Bone loss / osteoporosis pink checkmark
Cataracts pink checkmark
Bone fractures pink checkmark
Blood clots pink checkmark
Heart disease pink checkmark
Day-to-day tolerability concerns
Vaginal dryness, itchiness and discharge pink checkmark pink checkmark
Hot flashes/night sweats pink checkmark pink checkmark
Joint stiffness/pain pink checkmark
Muscle pain pink checkmark pink checkmark
Sexual dysfunction pink checkmark pink checkmark

What if you are considering extending therapy beyond 5 years. . .

Discuss the potential benefits and risks of continuing treatment with your doctor, and be sure to tell your doctor if you are experiencing any discomfort or symptoms. Keep all appointments with your care team and take your medications as prescribed by your doctor.

It is important to weigh the RISK of the cancer returning vs. the potential BENEFITS and possible SIDE EFFECTS of continuing anti-estrogen therapy beyond 5 years. Talk to your doctor to see how Breast Cancer Index may be able to help with your decision.

Learn more about how Breast Cancer Index can help you and your doctor make an informed decision to extend or end anti-estrogen therapy after 5 years.