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Arimidex or Tamoxifen Reduce Recurrence Risk After DCIS Equally Well in Postmenopausal Women, Choice Depends on Age, Side Effects

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DCIS (ductal carcinoma in situ) is the most common form of non-invasive breast cancer and is considered stage 0 cancer. While DCIS isn’t life threatening, it increases the risk of developing invasive breast cancer later in life.

DCIS usually is treated with surgery to remove the cancer -- lumpectomy in many cases. After surgery, many women have radiation therapy to reduce the risk of DCIS coming back (recurrence). If the DCIS is hormone-receptor-positive (most are), hormonal therapy also usually is recommended after surgery.

Of the adjuvant hormonal therapy choices, tamoxifen has been approved the longest and is approved to treat both premenopausal and postmenopausal women. Tamoxifen comes in both pill and liquid form and is usually taken once per day.

Aromatase inhibitors are the other main type of hormonal therapy medicine and are approved to treat only postmenopausal women. The aromatase inhibitors are:

  • Arimidex (chemical name: anastrozole)
  • Aromasin (chemical name: exemestane)
  • Femara (chemical name: letrozole)

Each is a pill, usually taken once a day. All three are available as generic medicines.

Two studies looked at the effectiveness and side effects of Arimidex and tamoxifen to reduce recurrence risk after DCIS surgery and radiation in postmenopausal women. The studies found that Arimidex and tamoxifen both reduced the risk of recurrence (the cancer coming back) about the same amount, but there were differences in side effects between the two medicines.

The studies were presented on Dec. 11, 2015 at the 2015 San Antonio Breast Cancer Symposium and published at the same time in The Lancet. Read the abstracts of:

Marisa Weiss, M.D., chief medical officer and founder, talks about these studies:

While much research has been done looking at the effectiveness of tamoxifen versus the aromatase inhibitors for reducing recurrence risk after invasive breast cancer, not much research has compared the two types of hormonal therapy for reducing recurrence risk after DCIS.

In the first study, the IBIS-II DCIS trial, the researchers randomly assigned 2,980 postmenopausal women diagnosed with DCIS who had lumpectomy followed by radiation to receive either Arimidex or tamoxifen for 5 years after radiation was completed.

The women were followed for about 7 years.

The researchers found that Arimidex and tamoxifen were equally effective at reducing the risk of DCIS recurrence, as well as reducing the risk of invasive cancer. The women who took Arimidex had slightly better outcomes, but this difference wasn’t statistically significant, which means that it could have been due to chance and not because of the difference in treatment.

About 67% of the women in each group completed the 5 years of hormonal therapy.

As the researchers expected, the two treatments caused very different side effects.

Women who took tamoxifen had more:

  • ovarian, endometrial, and skin cancers
  • blood clots
  • hot flashes
  • vaginal bleeding
  • vaginal discharge

Women who took Arimidex had more:

  • strokes
  • heart problems
  • bone fractures
  • bone/joint pain
  • vaginal dryness

The second study, the NSABP B-35 trial, was presented by Patricia Ganz, M.D., professor of medicine and public health at the University of California, Los Angeles and member of the Professional Advisory Board.

The NSABP B-35 study design was very similar to the IBIS-II DCIS study: 3,104 postmenopausal women diagnosed with DCIS who had lumpectomy followed by radiation were randomly assigned to get either Arimidex or tamoxifen for 5 years.

While the NSABP B-35 study also collected information on recurrence rates, the researchers also wanted to know how the women in the study would describe how they were feeling while taking either hormonal therapy. Doctors call this “patient-reported outcomes.”

To do that, the researchers had 1,193 women in the study fill out questionnaires on their physical and emotional functioning and quality of life, as well as side effects such as hot flashes, vaginal dryness, and muscle and joint pain.

The women filled out the questionnaires:

  • before they started taking the hormonal therapy
  • every 6 months while they were taking the hormonal therapy
  • 1 year after hormonal therapy ended

The researchers also grouped the results by the women’s ages: younger than 60 and 60 years or older.

As in the IBIS-II DCIS study, the two medicines were equally good at reducing the risk of recurrence. Still, when the researchers looked at recurrence risk reduction in women younger than 60, they found that Arimidex was slightly better than tamoxifen. This difference was statistically significant, which means it was likely due to the difference in treatment and not just because of chance. Among women 60 and older, there was no real difference in recurrence risk reduction between the two medicines.

When looking at quality of life, overall, the women in both treatment groups had about the same quality of life and there were no changes in physical or mental function with either medicine. Still, there were some differences in specific side effects between the two treatment groups.

Women in both groups said they had more hot flashes after they started taking either hormonal therapy medicine, and the hot flashes were more severe in women taking tamoxifen. Still, Dr. Ganz said the severity was modest and the frequency of the hot flashes decreased over time. Hot flashes also were more of a problem for women younger than 60 compared to older women.

Women taking tamoxifen also had more difficulty with bladder control.

Women taking Arimidex had more muscle and joint pain, and this pain didn’t lessen over time. Arimidex also caused more vaginal dryness and this symptom was worse in younger women.

“Both medicines were well tolerated,” said Dr. Ganz, “but younger women had more side effects. But the severity of the side effects was modest, even though they were frequent.

“Both of these drugs are excellent and can reduce the risk for breast cancer recurrence,” she continued. “Physicians and patients need to use this information along with the main trial outcomes to choose the optimal treatment for each woman. This is part of personalized or precision medicine.”

If you’re a postmenopausal woman who has been diagnosed with DCIS and your doctor is recommending hormonal therapy after surgery and radiation, these two studies offer strong, reassuring evidence that both tamoxifen and Arimidex are equally effective at reducing the risk of DCIS recurrence as well as the risk of being diagnosed with invasive breast cancer.

When deciding on which hormonal therapy medicine to take, you and your doctor will consider a number of factors, including:

  • your age
  • your weight
  • your history of hot flashes
  • any history of vaginal dryness
  • any other health issues you have

If you start on one medicine and have troubling side effects, talk to your doctor. It’s likely you may be able to switch to the other.

For more information on hormonal therapy, including what to expect and side effects, visit the Hormonal Therapy pages.

Read more Research News from the 2015 San Antonio Breast Cancer Symposium:

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