Tamoxifen has been used for so long to treat breast cancer that most of us assumed we knew everything that we needed to know about it—including how long women should take it. But yesterday at the San Antonio Breast Cancer Symposium we all learned something new when researchers presented results from the ATLAS trial (Adjuvant Tamoxifen: Longer Against Shorter).

This large international trial included 6,846 women with early stage hormone-sensitive breast cancer who already had taken tamoxifen for five years. Half of the women took tamoxifen for five more years; the other half took a placebo. The results: After following the women for 10 years, the study found that the women who stayed on tamoxifen the additional five years were less likely to have a recurrence or die of breast cancer than were the women who had been on the placebo. Specifically, there were 617 recurrences and 331 deaths that occurred among the 3,428 women who stayed on tamoxifen compared to 711 recurrences and 397 deaths among the 3,418 women who were on the placebo.

This is not what most of us would have predicted—which again shows why clinical trials are so important. It also means we are now confronted with new questions about how best to use tamoxifen, and the aromatase inhibitors, to treat early-stage breast cancer.

The NSABP B-14 study told us that five years of tamoxifen was better than ten, which is what gave us our current standard of care: five years. Subsequently, when the aromatase inhibitors were compared against tamoxifen in clinical trials for early stage breast cancer in postmenopausal women, both drugs were given for five years. It wasn’t that we knew five years of an AI was best. We based what we did on what we had learned about tamoxifen. In these studies, the AI came out slightly ahead. So we changed the standard of care, recommending that postmenopausal women take an AI instead of tamoxifen. But then we learned that taking tamoxifen for two to three years and then an AI for the next two to three years was better than five years of an AI. And that became a new recommendation for postmenopausal women.

Throughout, for premenopausal women (who can’t take an AI because it’s only effective in postmenopausal women) the standard of care never changed: tamoxifen for five years. Now, it will.

For postmenopausal women there will also be new things to consider:

For postmenopausal women, is ten years of tamoxifen better than five years of tamoxifen and then five years of an AI? More studies will be needed to answer this question.

Should postmenopausal women go back on tamoxifen for five years after finishing their AI? Maybe. An AI keeps testosterone from being converted into estrogen, so it decreases estrogen throughout the body. But tamoxifen works in a different way. It blocks the estrogen receptor on cancer cells, but acts like an estrogen in the bone, liver and uterus. So, it would be easier to stay on longer.

What about other risks and benefits? Tamoxifen decreases cholesterol, and improves bone density, which is good for both pre- and postmenopausal women. The biggest risk is uterine cancer. This is less of a concern for premenopausal women—their risk of developing the disease is low to begin with—and this study did not find that tamoxifen increased their risk. However, the risk did increase in postmenopausal women.  It’s not a huge risk, but it’s real.

What should you do? It all depends on whether you are premenopausal or postmenopausal. If you are premenopausal and do not go into menopause during your five years on tamoxifen, then it makes sense to stay on it another five years. If you are postmenopausal, it depends on what you can tolerate. If the side effects of the AI are too much, it makes sense to go back on tamoxifen.

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9 Responses to From San Antonio, Unexpected News About Tamoxifen

  1. Jacqui says:

    I am a woman on AI for 4 years now and assuming I am going into my last year of this beast of a drug. I was diagnosed in 2008 with estrogen positive stage 1 breast cancer , had a bi lateral mastectomy and did not have any chemo or radiation therapy. I was put on Aromosin and told to that i would be on it for five years. I was never on tamoxifen first. It was explained to me that it was a step that could be skipped because i had a hysterectomy at the age of 35 in 1989 and had been on HRT until the time of my diagnosis. At my last oncology appt in July it was suggested that I see a endocrinologist because my bone density is so low and I have been diagnosed with severe osteoporosis ( with levels of about an 85 yr old woman with osteoporosis). I will see that dr and my oncologist again in feb. At that time my oncologist stated she would make the decision about whether I should continue with the Aromosin for the 5th year of treatment ( until NOV 2013). At this point would I be better to stay on the aromosin for the remainder of my treatment or should tamoxifen be a suggestion for the next 5 years. I am concerned about the condition of my bones and have had several breaks and cracks in various bones over the last 4 years including a compression fracture in my vertebrae. deciding what is the best route to take is causing me much anxiety as i would neither want to have a occurrence of cancer but also fear the negative outcome of having such and extreme case of osteoporosis and the complications it can create for my health and well being. Any one have any suggestions or ideas …. my poor husband can’t take many more sleepless nights with me… thank you to all that read this and listened to my fears and i wish all of you who are struggling with this disease all the best ….

  2. It’s hard simply because I had expectations that after five years, I could leave the treatment behind . . . I think it might take some time to readjust my approach to extending tamoxifen another five years. But we’ll see. Thank you for this breakdown, it’s helpful. ~Catherine

    P.S. I am curious what the difference is between the original study that suggested 5 years, and these new 10 year results. Is there an explanation for the discrepancy?

  3. Dr. Susan Love says:

    The NSABP study compared five years to 10 years and then compared each group at 12 years. They were comparing the women who had just finished 10 years with the women who had stopped after five.

    The ATLAS study found little difference between the two groups at year 10 but it followed both groups of women for five more years. At 15 years–five years after the the had taken the drug for 10 years–was when they found the significant difference.

    The ATLAS study was significantly larger as well (6846 women vs 1172 women). So the combination of a larger study and longer follow up allowed them to identify a benefit. The effect took longer to see because ER-positive cancers tend to grow more slowly.

  4. Jonathan says:

    What the study did point out (which is easy to overlook) is that roughly half of the participants were node positive. You have to wonder if women with stage I disease are a group that will do fine with just standard 5 year therapy. So, one question to ask is how many women, depending on node involvement, relapsed, regardless of how long they took tamoxifen?

    Another aspect to consider is why treatment CURES some women but merely CONTROLS the disease in others. I remember when my mom was diagnosed in 1995 with highly aggressive stage II disease and the oncologist said that she’d be on tamoxifen for life. But in 2000 when data suggested worse outcomes with extended therapy, he took her off it at the 5 year mark. (Thankfully she’s fine at 17 years.) Either way, why is this new data so different from the older? Weren’t they both randomized clinical trials?

  5. Sia says:

    I am post menopausal and have been on AI for over 4 years. I was diagnosed with stage 1C breast cancer and also had vascular invasion. I had bilateral mastectomies and chemo. I am very anxious about the next step and am eager to continue with whatever drug (tamoxifin or AI ) will bring the most benefit. I understand that a Mass General study on AI will help to answer these questions in 2013. Are there other studies that are working on the question of the next step for postmenopausal women who are coming off of 5 years of AI ? Thanks

  6. Cheryle says:

    I was diagnosed with stage 3 IBC (Inflammatory Breast Cancer) in 2008. I was in remission by 2010. I have not taken any anti cancer medication since the beginning of 2011 due to the side affects. I was given Tamoxifin as part of my treatment. What does this mean for me?

  7. Tammie says:

    I was wondering what the current research suggests about antidepressents rendering Tamoxifen less effective. I have a friend with breast cancer for the second time and her pharmacist recently dicussed this with her. When she discussed this with her oncologist he researched it and seemed surprised to find the information accurate.

  8. Jude Moreno says:

    I was 34 when diagnosed with Breast Cancer in 2005. I had surgery, radiation and chemo (1/7 lymph nodes positive) it was estrogen receptor positive. I was then on Tamoxifen from 2006–2011. Now I am confused, I am not sure what to do about going back on Tamoxifen. My oncologist said its up to me, that he thinks more studies are needed. He thinks that there is probably little to no benefit, especially when a risk/benefit analysis is done, for me going back on Tamoxifen for 5 more years. I have had normal periods since the Tamoxifen was stopped in July of 2011. Could you please help me figure out what to do?

  9. Becky Merritt says:

    I am 50 years old and was diagnosed in 2010 with estrogen receptor pos. with mets to the bone. I was placed on tamoxifen, but after a year and a half was told that I had become imune to the tamoxifen because my ca 2729 started to increase. I had my ovaries removed and have been on several AI s. My counts had continued to go up. I am currently on chemo,(taxol). After chemo can I go back on the tamoxifen again or will I still be imune to it?? is there any other option?? Please help

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