Many women who are premenopausal at the time of diagnosis may pass through menopause by the time they finish tamoxifen or experience early menopause as a result of chemotherapy. This is an important point in trying to weigh how beneficial the extra treatment really is for premenopausal women.
In absolute terms, continuing on tamoxifen kept three additional women out of every 100 from dying of breast cancer within 5 to 14 years from when their disease was diagnosed.
In the Atlas trial, it appears that roughly 40% of the patients assigned to take tamoxifen for the additional 5 years stopped prematurely. This could have an impact on the results of this study and more discussion should have been given about limitations of the results.
According to Dr. Silvana Martino, chair of the Southwest Oncology Group (SWOG) breast cancer committee at the time, the decision, almost 20 years ago, that 5 years of tamoxifen as adjuvant treatment for early breast cancer was the optimal length of time, the data available to them were from two studies comparing 5 years of tamoxifen versus long use.
Those results demonstrated that women treated for long than 5 years had more side effects, especially endometrial cancers, and that they did not have less breast cancer recurrences. In fact, there was a suggestion that there might be more recurrences with longer use. The decision was not unanimous, in part, because some felt that there were too few node positive patients included in the two studies.
Two additional studies had continued to look at this question. They were the ATLAS and the ATOM trials. The ATLAS trial was a large international study with long term follow-up. The results from ATLAS demonstrated that there is better survival for women treated with tamoxifen for 10 years rather than 5 years. The difference is most apparent in years 10-15 from the time of starting therapy.
This information is not applicable to women who are taking aromatase inhibitor hormones. It is applicable to women with invasive breast cancer who are usually treated with tamoxifen. Therefore, it applies primarily to premenopausal women and to postmenopausal women who cannot tolerate aromatase inhibitors and are treated with tamoxifen.
It does not apply to women treated for DCIS or women who have not had breast cancer but are at high risk when tamoxifen is being used as a preventive dug. They are still awaiting mature results from the ATOM trial.
http://cancerfocus.org/forum/showthread.php?t=3863