Who wouldn’t be drawn in by this headline: Breast Cancer Risk Slashed by Hormone-Blocking Pill, Study Shows. But as is so often the case, the headline doesn’t tell the whole story.

As you’ve probably seen, the media have been reporting findings from the MAP.3 (mammary prevention-3) trial that were presented this week at the American Society of Clinical Oncology meeting in Chicago and simultaneously published in the New England Journal of Medicine.

The trial followed more than 4,500 women over a five-year period. To enroll in the study, a woman had to be 35 years of age or older, post-menopausal, and at increased risk of developing breast cancer because of her age (60 or over) or Gail risk score or because she had previously been diagnosed with atypical hyperplasia, or lobular carcinoma in situ (LCIS), or ductal carcinoma in situ (DCIS) that was treated with a mastectomy. The trial was not open to women who were known to have a BRCA1 or BRCA2 mutation.
Half of the women were randomized to the group that received the aromatase inhibitor exemestane (brand name Aromasin). The other half received a placebo. At a median follow-up of three years, the researchers found that the group of women receiving exemestane had a 65 percent reduction in invasive cancers.

That sounds impressive, but this is what it means in real numbers: There were 11 invasive cancers that developed in the 2285 women who were given exemestane, compared to 32 in the 2275 women who took the placebo. This means the drug prevented 21 cancers. In addition, fewer cases of DCIS, LCIS, and atypical hyperplasia were found in the group receiving exemestane: there were 9 diagnoses of DCIS in the exemestane group compared to 14 in the placebo group, and there were 4 cases of atypical hyperplasia and LCIS in the exemestane group compared with 11 in the placebo group.

MAP.3 is the first randomized trial to report on the use of an aromatase inhibitor for breast cancer risk reduction. While I applaud the focus on prevention, I am not sure exemestane is the answer we have been looking for. First of all, this drug can only be used in postmenopausal women. (Only postmenopausal women can use an aromatase inhibitor. That’s because postmenopausal women get most of their estrogen from the conversion of androgens into estrogen by the aromatase enzyme, while premenopausal women get most of their estrogen directly from their ovaries.)

Furthermore, most of the cancers prevented were the so-called “good” ones–invasive and noninvasive (DCIS) that are estrogen receptor (ER)-positive, HER2-negative, and node negative. These tend to be more common in postmenopausal women and have a good prognosis.

In addition, the discussion about side effects—in the article, and by the media—are a bit misleading. It is true that exemestane does not have the same side effects as tamoxifen which has a different mechanism of action. But because aromatase inhibitors like exemestane blocks estrogen production throughout the body, they have their own side effects, such as arthritis and joint pain, hot flashes, sexual problems, fatigue, and insomnia. These were dismissed as not serious, but it should be noted that one-third of the women on exemestane stopped taking it during the three years of the study. There was some bone loss as well but no increase in fractures. This is not surprising, since the median time women were studied was three years, and the median age of the participants was 62, which is before the major risk for fracture develops.

It also is not known how long women would need to take exemestane to benefit. There is some suggestion from the cancer data that the protective effect might persist after the drug has been stopped, but I wonder if doctors and patients will be willing to test that hypothesis.

Currently, two drugs are FDA-approved for breast cancer prevention in high-risk women, tamoxifen and raloxifene. (Tamoxifen has been used as a breast cancer treatment for decades. Raloxifene is not used to treat breast cancer.) Studies have shown that these drugs also reduce breast cancer risk, but with no change in the mortality of the disease. This will most likely be true for exemestane as well. Also, as the study’s author’s note, many high-risk women have chosen not to take tamoxifen or raloxifene, because they believe the risks from the side effects do not outweigh the benefits. Currently, only about 4 percent of women who are at increased risk for breast cancer have chosen to take either of these drugs.

We desperately need ways to prevent breast cancer but so far all our approaches have been aimed at postmenopausal women with relatively good prognosis lesions. We need to focus on finding a way to prevent the more aggressive cancers that are killing premenopausal women around the world—a much more difficult goal. We need to find the cause of the disease, and stop it once and for all. Women can help this effort by joining the Love/Avon Army of Women. By taking part in the research, we can be the generation that stops all breast cancer once and for all.

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12 Responses to Exemestane for Prevention: Parsing the News

  1. Pink Kitchen says:

    I am so thankful that you’re helping survivors to unravel the details behind these drugs. Keep up the good work.

  2. Maureen B says:

    Thank you for examining the results and writing an easy to understand discussion of the results.

    I was diagnosed at 39, have lived with the disease for almost 15 years and now have a 4th site of mets in spinal fluid in brain.

    Please continue your most powerful work.

  3. mona eskandarian says:

    thanks for all the info. i have lcis and i am 56 yers old i have find out about it 3 years ago, i am not taking any medication due to the side efects.this info helps me a lot. thanks again

  4. Debbie B says:

    Thank you so much for this easy to understand explanation of the the results of this study. Once again the media is not really giving the whole picture. I am one of those who decided not to take tamoxifen as I strongly felt the risk of its side effects out weighed the potential benefit in my particular case. I follow all reports on breast cancer fighting drugs with great interest.

  5. Mary says:

    Thank you Doctor Love, for emphasizing the realities of this study as opposed to the hyperbole we are fed by the media and, too often, by the study directors themselves. This study and the media emphasized the relative benefits rather than the absolute benefits of Aromasin. We, mere mortals, tend to think in absolutes. How many women were deceived into believing they would have an absolute benefit of 65%, from this drug as opposed to the miniscule absolute benefit that is the reality? Too often, even with BC treatment we are given the relative benefit and not the absolute benefit of therapy. I was given the relative benefit of Herceptin, by an oncologist, who I suspect was thinking in absolutes. After teasing out the numbers I found that the 55% relative benefit was an absolute benefit of roughly 6% That was not good enough given the 6% absolute risk of heart issues from the drug. I ultimately refused Herceptin, AC chemo and the aromatase inhibitors. For me the absolute benefits were not good enough and I choose quality of life as my number one goal. That was over 5 years ago.

  6. Roni J. says:

    I was diagnosed with Inflamatory Breast cancer 9 years ago and after a year of treatment, have been on Arimidex/Aromasin for 8 and a half years. I understand that after 10 years, the risk of heart complications had been identified. In a year and a half, I will need to go off Aromasin for this reason, yet fear the return of IBC. I need as much information as possible to participate with my doctor in making this decision. thanks

  7. Musa Mayer says:

    I too was at ASCO and heard the MAP.3 data presented…but I also heard several presentations on the concerning issue of non-compliance with aromatase inhibitors for the TREATMENT of breast cancer. This is obviously a much higher risk group, at risk of recurrence and death from the disease, yet multiple studies suggest that as many as 50% of patients prescribed an AI are non-compliant, for a variety of reported reasons. What makes us think that women who don’t have breast cancer–and are far more likely than not ever to be diagnosed–will happily take Aromasin for “prevention” (really risk reduction)?

  8. Yvette says:

    Thank you for making sense of the study. I recommend you to everyone. I did take Tamoxifen faithfully and developed breast cancer. I am now taking Femara faithfully because I just don’t know what else to do. Keep up the great work. This is a scarey road to travel.

  9. Judy KR says:

    I am 69, diagnosed with LCIS last January
    (2011) when I was 68. I was reluctant to take Tamoxifen and Evista due to worry about side affect (notably Uterine Cancer and Blood clots). Evista (reloxifene) seemed like a better bet, and I was considering it. Then the study of Aromasin came out, and I decided to take it. However, I haven’t yet taken it and it has been a full year. I did not realize it was
    chemotherapy which concerns me and
    there are several other concerns some of
    which became clear in your summary.
    It isn’t really clear how much prevention this drug actually provides. It was interesting to find out that many people
    dropped out of the study before three years. I am beginning to feel not enough is known about this drug.
    I also have the problem of being overweight by 30 – 35 lbs. All of these drugs contribute to gaining weight since
    estrogen is blocked. I am beginning to feel
    that I may be better off not taking a drug and just being monitored frequently.
    I would love a comment from you on my situation, if that’s possible.
    If not, I will continue to do research and be monitored and hope you address the
    issues presented by Aromasin again.

    Thank you for your analysis of the study in June.

  10. Mary Stevens says:

    I was diagnosed in 2006 at the age of 41 with infiltrating lobular breast cancer with 4 lymph nodes in the breast and 23 nodes under the arm positive. Surgery, chemo, radiation, tamoxifen for 3 years and 2+ ( I am still taking it) years of Aromasin. Approximately 4 months after I started taking the Aromasin I developed severe heart failure was hospitalised for 10 days and now live with Dilated Cardiomyopathy I am taking lot of medication everyday for my heart as well as the Aromasin. Could the Aromasin have been responsible for my heart failure? I am breathless all the time. Could this be the Aromasin.? When should I stop the Aromasin.?

  11. Nancy says:

    I was diagnosed with atypical hyperplasia vs LCIS years ago and took tamoxifen for 5 years. Now I see there was a study on continuing tamoxifen longer. I’m not sure if I should go on it again or not. Comments? I’m 58

  12. Lynn Busch says:

    Have been diagnosed with atypical Hyperplasia cells in lobular region of left breast. Picked up by ultrasound and MRI. (dense breasts) Followed up by surgery to clean out the area. Was sent to an oncologist who strongly recommends the use of aromasin for 5 years as a preventative. Only family history is maternal grandmother diagnosed in her mid 70′s. Lived to 90. I am age 60 and my mother (83) is still alive. Not sure what to do. would love to hear from others with same situation. Oncologist said it would reduce risk by 65% but don’t know whether this is accurate. Thanks for advice.

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