Breaking News from San Antonio: Tamoxifen for 10 Years?

I’m at the San Antonio Breast Cancer Symposium and as you may have seen on Facebook, Twitter, and the news, study results from the ATLAS trial were released here yesterday.  The study suggested that taking Tamoxifen for 10 years, instead of stopping after five years, may be beneficial for estrogen-receptor positive women diagnosed with breast cancer.  But what do these study results really mean and how will they impact young women?

Currently, premenopausal breast cancer patients who are estrogen-receptor positive (their cancer grows in the presence of estrogen) are prescribed Tamoxifen for a course of five years.  The Adjuvant Tamoxifen:  Longer Against Shorter (ATLAS) trial, examined whether there was benefit in continuing Tamoxifen for five more years, for a total of ten.  Study results were reported at the San Antonio Breast Cancer Symposium yesterday and released the same day online in The Lancet.

In the ATLAS study, 6,846 estrogen-receptor positive women around the world were randomly allocated to two groups.  The five-year group stopped taking Tamoxifen at the five-year mark.  The 10-year group continued taking Tamoxifen for another five years.  After 7.6 years of follow-up, study results show a reduced risk of recurrence, reduced breast cancer mortality, and reduced overall mortality, in those women who stayed on Tamoxifen for 10 years.  Patients in the study were 80% compliant with taking their medication.

While a benefit was seen in this study to continuing Tamoxifen for five additional years, these benefits were modest.  Between years 5 to 14 after initial diagnosis, breast cancer mortality was 15% for those women who stopped Tamoxifen at 5 years and 12.2% for women who continued for 10 years.  The cumulative risk of recurrence during years 5 to 14 was 21.4% for women who took Tamoxifen for 10 years, compared to 25.1% in the group who stopped at five years.

Overall, the patient population in this study tended to have low nodal involvement and most participants were over the age of 45 at time of initial diagnosis.  53% of the 10-year group were node negative and 54% of the five-year group were node negative.  Only 16% of both groups had four or more nodes involved.  Also, only 19% of the 10-year group and 18% of the five-year group were under age 45 at time of diagnosis.  In both the five and 10-year group, 89% of study participants were postmenopausal at time of their entry into the ATLAS trial.  In the five-year and 10-year groups , 47% and 48% of patients respectively had tumor sizes ranging from 1 to 20 mm (equivalent to 2 cm or under), while 39% and 38% respectively had tumor sizes between 21-50 mm (2 to 5 cm).

Tamoxifen also has its risks and side effects and the longer treatment did increase side-effects.  In particular, the women who continued on Tamoxifen for 10 years had a higher rate of endometrial cancer (3.1%; 116 occurrences) than those who stopped at year five (1.6%; 63 occurrences), between years five to 14.  The authors stated that this risk is more pronounced in postmenopausal women and that there would be “little risk” to premenopausal women of endometrial cancer.  While death from stroke or pulmonary embolism were comparable between the five-year and 10-year groups, a table showing “Non-neoplastic disease; ever hospitalized or death” shows a higher number of strokes (130 to 119), pulmonary embolus (41 to 21) and Ischemic heart disease (127 to 63) in the 10-year group compared to the five-year group.

Overall, more data is needed and ATLAS data will continue to be gathered and analyzed.  The study authors noted that trials comparing 10 years to five years will need to be followed up for at least 15 years from diagnosis, given the fact that the protective effects of Tamoxifen extend beyond the time that it is taken.  “Longer follow up of ATLAS (and a meta-analysis of all such trials) will be needed to assess the full benefits and hazards throughout the second decade.”  In addition, more data is needed on younger women.

So, what does this study mean for young women diagnosed with breast cancer?

First, if you are estrogen-receptor positive and have been prescribed Tamoxifen, this study supports the benefits of that medication.  Even if you take only five years of Tamoxifen, the benefit of that treatment continues throughout the first 15 years after diagnosis.  Second, if you are a longer-term patient, who is about to complete their five years of Tamoxifen or have completed your five years recently, you may want to speak with your physician about continuing the medication.  The results of this study support that decision, but as noted above, there are drawbacks as well and the benefits appear to be modest.   In addition, there are other side effects to Tamoxifen not examined in this study, including hot flashes and weight gain, which may impact your quality of life.  You will need to discuss your medical history with your oncologist to weigh the risks versus benefits of continuing on Tamoxifen.

Finally, a particular concern with this study is the impact that this study may have on young women’s family planning.  Many young women already wait until they have completed their five-year course of Tamoxifen before trying to start a family.  Will this study cause that delay to become 10 years?  And, are the modest benefits shown in this study worth that?  That is a very personal decision and again, we recommend speaking with your physician.