Arimidex and Aromasin Equally Good at Reducing Recurrence Risk

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A study found that two aromatase inhibitors -- Arimidex (chemical name: anastrozole) and Aromasin (chemical name: exemestane) -- were equally good at reducing the risk of recurrence (the cancer coming back) in postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer. The results were presented at the 2010 San Antonio Breast Cancer Symposium (SABCS).

Many women take hormonal therapy medicine -- either an aromatase inhibitor or tamoxifen -- after surgery and other treatments for hormone-receptor-positive, early-stage breast cancer to reduce the risk of recurrence. Hormonal therapy given after surgery is called adjuvant hormonal therapy.

There are three aromatase inhibitors: Arimidex, Aromasin, and Femara (chemical name: letrozole).

Aromatase inhibitors interfere with the activity of a protein called aromatase. Aromatase allows certain body tissues (ovaries, liver, kidneys) to make the hormone estrogen. So aromatase inhibitors reduce the amount of estrogen in your body, which makes it hard for hormone-receptor-positive breast cancers to grow. Rather than reducing estrogen, tamoxifen blocks the effect of estrogen on breast cancer cells by sitting in the cancer cells' estrogen receptors.

Most doctors prescribe one hormonal therapy medicine -- either tamoxifen or an aromatase inhibitor -- for 5 years. This is called monotherapy. Arimidex is approved by the U.S. Food and Drug Administration (FDA) to be given as monotherapy. Aromasin is not approved by the FDA to be given as monotherapy, but many doctors use it this way. Other doctors prescribe tamoxifen for 2 or 3 years and then switch to an aromatase inhibitor until hormonal therapy has been taken for a total of 5 years. This is called sequential therapy. Aromasin is approved by the FDA to be used in sequential therapy, after tamoxifen has been taken for 2 or 3 years.

There are some chemical differences between the three aromatase inhibitors, so some doctors believe that there may be different benefits and risks for each, depending on each woman's unique situation. This large study, called the MA.27 study, compared the outcomes of 7,576 women diagnosed with hormone-receptor-positive breast cancer and treated with Arimidex or Aromasin for 5 years after surgery:

  • half the women were older than 64
  • 71% had cancer in one or more lymph nodes
  • 70% had lumpectomy followed by radiation; 30% had mastectomy
  • about 33% also had chemotherapy after surgery to reduce the risk of recurrence
  • 4% were diagnosed with HER2-positive breast cancer and also were treated with the targeted therapy Herceptin (chemical name: trastuzumab)

After surgery and any other treatments, half the women took Arimidex while the other half took Aromasin. When hormonal therapy was started, the women planned to take whichever aromatase inhibitor they were prescribed for 5 years.

After 4 years, the likelihood of being alive with no cancer recurrence (disease-free survival) as well as the likelihood of being alive (overall survival), was the same in both groups:

  • 90.8% of the women who took Aromasin and 90.9% of the women who took Arimidex were alive and had no recurrence after 4 years
  • 94% of the women in both groups were alive after 4 years

There were differences in side effects between the two aromatase inhibitors.

About 1% to 2% of the women who took Aromasin had one or more of these side effects:

  • an abnormal liver blood test (liver enzyme elevation)
  • acne and/or or other male hormone changes, such as facial hair growth (androgenic changes)

These side effects were rare with Arimidex.

High triglyceride and cholesterol levels were more likely in women who took Arimidex compared to women who took Aromasin:

  • 3% of women who took Arimidex had high triglyceride levels compared to 2% of women who took Aromasin
  • 18% of women who took Arimidex had high cholesterol levels compared to 15% of women who took Aromasin

Osteoporosis was more likely in women who took Arimidex compared to women who took Aromasin:

  • 35% of women who took Arimidex developed osteoporosis compared to 31% of women who took Aromasin

Hot flashes and night sweats (vasomotor symptoms) are side effects of both tamoxifen and the aromatase inhibitors, though they're more common with tamoxifen. Joint pain is a more common side effect of the aromatase inhibitors. Both tamoxifen and the aromatase inhibitors can lead to dangerous blood clots in rare cases, but blood clots are more likely with tamoxifen. Aromatase inhibitors can weaken bones (osteoporosis) and make women more likely to break a bone.

The American Society of Clinical Oncology (ASCO) issued new guidelines about adjuvant hormonal therapy medicines in July 2010. ASCO is a national organization of oncologists and other cancer care providers. Based on a number of studies showing that women treated with an aromatase inhibitor are somewhat less likely than women treated with tamoxifen to have a recurrence, ASCO recommends that an aromatase inhibitor be preferred over tamoxifen as the adjuvant hormonal therapy choice. ASCO doesn't recommend one aromatase inhibitor over another -- they're considered interchangeable. If side effects from one aromatase inhibitor are intolerable, switching to a different aromatase inhibitor rather than tamoxifen may make sense. Still, there are differences in side effects between tamoxifen and the aromatase inhibitors; based on these differences, tamoxifen may be a good choice for some women.

Tamoxifen and Arimidex are available as generic medicines, so may be much less expensive than Aromasin and Femara (depending on insurance coverage).

If you're a postmenopausal woman who's been diagnosed with hormone-receptor-positive, early-stage breast cancer, keep two things in mind when you and your doctor are deciding on adjuvant hormonal therapy:

  • Every woman responds differently to treatment. What works for someone else may not work for you and what works for you may not work for someone else.
  • Your treatment plan isn't written in stone. You can always switch medicines if another treatment has greater benefits and/or fewer side effects.

It's a good idea to ask your doctor about the differences in benefits and side effects between aromatase inhibitors and tamoxifen, as well as the pros and cons of monotherapy vs. sequential therapy based on your unique situation. Together, you can decide on a treatment plan that's best for YOU.

Once you've started on adjuvant hormonal therapy, do your best to STICK WITH your plan. The medicine can't work if you don't take it. One disheartening MA.27 result was that 30% to 40% of the women had stopped taking the hormonal therapy medicine 4 years into the 5-year treatment plan. Side effects were probably (and understandably) the reason the women stopped treatment. Still, other factors may have played a role in the women's risky decision to stop hormonal therapy early:

  • Some women need to put everything related to cancer behind them after the initial diagnosis and treatment.
  • Lingering depression from diagnosis and initial treatment also may play a role.
  • The cost of hormonal therapy is a reason for some women.
  • Some women may not understand how important adjuvant hormonal therapy is or don't have good communication with their doctors.

Still, all these reasons are overshadowed by the fact that breast cancer can come back. Taking hormonal therapy for 5 years after surgery reduces that risk. Anyone prescribed adjuvant hormonal therapy must remember this.

There are ways to get rid of any obstacles that stop you from completing 5 years of hormonal therapy. If side effects are a problem, talk to your doctor about how to manage them. Remember that you also may be able to switch to a different hormonal therapy medicine. No matter the reason, if you're thinking about stopping hormonal therapy early, talk to your doctor about ways you can stick to your plan.

For more information, visit the Breastcancer.org Staying on Track with Hormonal Therapy page. You can read about why it's so important to stick to your treatment plan, as well as ways to manage side effects.

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