Understanding Hormone Therapy Drugs

Patient Expert

Up to 80 percent of women diagnosed with breast cancer take tamoxifen, Arimidex, Femara, or Aromasin to help prevent a cancer recurrence. This hormone therapy lasts for years, well after active treatment—surgery, chemo, radiation—is complete. How do these drugs work? And what’s their downside?

When are hormone therapy drugs recommended?

When you’re diagnosed with breast cancer, your oncologist will tell you whether or not your cancer is “hormone-receptive” (a.k.a. “hormone-positive,” “ER/PR+”). If positive, your particular cancer relies on the female sex hormones (chiefly estrogen, sometimes progesterone) to live. Without access to these hormones, the cancer cells die. Hormone therapy drugs work by depriving cancer cells of the life-sustaining hormones they need.

Most breast cancers – about 80 percent – are hormone-receptive. Thus most women are eligible for hormone therapy (which is different than the hormone replacement therapy you might take to combat menopausal symptoms – don’t get confused!).

Hormone therapy (HT) doesn’t come without a downside – mainly, side effects ranging from uncomfortable to downright dangerous, plus cost. Thus some women choose to forego HT. But most at least give it a try.

How does my doctor decide what drug I should take?

There are two types of hormone therapy drugs: aromatase inhibitors (AIs), which are given chiefly to women who’ve been through menopause; and tamoxifen (Nolvadex), given to pre-menopausal women. There’s some occasional crossover, with post-menopausal women receiving tamoxifen, or pre-menopausal survivors taking AIs, but it’s rare.

How do AIs (Arimidex, Femara, Aromasin) work?

Once a woman has been through menopause her ovaries shut down, and estrogen production is cut way back. Still, women need a minimal amount of estrogen for functions other than child-bearing; so a particular enzyme, aromatase, kicks into gear.

Aromatase turns the hormone androgen (whose levels aren’t affected by menopause) into estrogen. AIs do exactly what they say: inhibit aromatase from creating estrogen. How? By binding themselves, either temporarily (Arimidex, Femara) or permanently (Aromasin) to aromatase so that it becomes dysfunctional – and can no longer turn androgen into estrogen.

No estrogen = no nourishment for cancer cells = no cancer recurrence.

How does tamoxifen work?

Tamoxifen works by attaching itself to special receptors on cancer cells designed to capture estrogen, effectively crowding estrogen out of the picture. Breast cancer cells deprived of estrogen go dormant, and almost always eventually die; some even die immediately.

How long will I take these drugs?

There’s no simple answer; duration of treatment will depend on a number of factors, including the following:

•How aggressive/advanced your cancer was;

•Which drug you’re taking;

•How well you tolerate the treatment;

•Advances in research.

Currently, it’s recommended tamoxifen be taken for up to five years, while the recommendation for AIs is five to 10 years. These figures continue to evolve, though, as survival data continues to accumulate. The more serious your cancer, the more concerned your oncologist is with a recurrence, the longer you’re likely to continue hormone therapy.

Many women aren’t able to complete the full recommended course of hormone therapy drugs, due to side effects. While doctors do everything they can to deal with side effects and keep their patients on hormone therapy as long as possible, ultimately it’s a woman’s decision to weigh quality of life vs. chance of recurrence.

So, what kind of side effects are we talking?

AIs can produce bone and joint pain ranging from barely noticeable to disabling. They also diminish bone mineral density, with the potential for onset of osteopenia/osteoporosis.

Tamoxifen’s side effects mimic those of menopause, chiefly hot flashes, mood swings, and loss of libido. Tamoxifen also increases the risk of endometrial cancer – though the risk remains very low.

Finally, though this isn’t a recognized side effect, many women report gaining weight while taking tamoxifen – though thankfully, those same women say they’re able to lose the extra pounds once they finish treatment.

See more helpful articles:

How Do Hormones Fit Into Breast Cancer Treatment?

Hormone Drugs and Bone Loss: Beware Hidden Damage

Hormone Replacement Therapy vs. Hormone Therapy: What’s the Difference?

Aromatase Inhibitor FAQS

Tamoxifen FAQS

Breast cancer survivor and award-winning author PJ Hamel_, a long-time contributor to the HealthCentral community, counsels women with breast cancer through the volunteer program at her local hospital. She founded and manages a large and active online survivor support network. _