• Although there were many meaningful announcements from the first two days of this year’s San Antonio Breast Cancer Symposium the release of a major study on adjuvant tamoxifen treatment was perhaps the most important.
  • The tamoxifen study, which gathered information from more than 6,800 women with estrogen receptor positive (ER+) breast cancer, showed a significant reduction in the reoccurrence of breast cancer.
  • This could be a noteworthy step to augment our ability to improve breast cancer survivorship – roughly 75% of breast cancers are ER+.

Background on Tamoxifen

Although tamoxifen was originally discovered in the 1960’s the US Food and Drug Administration (FDA) didn’t approve tamoxifen for the treatment of breast cancer until 1977. Early clinical trials for tamoxifen didn’t prescreen patient tumors for different types of breast cancer based upon the estrogen receptor (hormones).

As a result, tamoxifen was widely prescribed after primary breast cancer treatments (surgery, radiation therapy, etc.). Of further note, large tamoxifen clinical trials in the 1980’s failed to demonstrate a rate of major survival for patients with breast cancer (independent of receptor status).

New tamoxifen studies in the 1990’s began to prescreen patients for estrogen receptor subtypes (+/-) breast cancer. In 1998 a massive study demonstrated that “some years of adjuvant tamoxifen treatment substantially improves the 10-year survival of women with ER-positive tumors.” As a result of this, and other studies, the standard treatment for women with ER+ breast cancer was to take up to a five-year regimen of Tamoxifen.

  • AstraZeneca’s patent on the chemical compound expired in 2002.
  • Tamoxifen is now widely available in generic form.
  • It is important to note research indicates the effectiveness of tamoxifen is inhibited when taken in combination with selective serotonin reuptake inhibitors (SSRIs). SSRIs include Paxil, Prozac and Zoloft, amongst others.

The International Adjuvant Tamoxifen – Longer Against Shorter (ATLAS) Study

ATLAS started in the mid 1990’s and is “designed to determine reliably the optimal duration of adjuvant tamoxifen in early breast cancer.” During the San Antonio Breast Cancer Symposium, on December 5, ATLAS released the results of their most recent study that showed deaths attributed to ER+ breast cancer are reduced by nearly 50% with a 10-year tamoxifen treatment regimen.

This is a notable improvement from the current five-year tamoxifen treatment plan, which has been shown to reduce ER+ breast cancer mortality by almost a third. The ATLAS study is scheduled to continue until 2015, when the long-term follow-up for all ATLAS patients will be released.

Notable Side Effects from the Study Released during the San Antonio Breast Cancer Symposium

  • The rate of endometrial cancer (uterus) was 3.1% for women participating in the study and took tamoxifen for 10 years. The rate for women who stopped after five years was 1.6%.
  • The death rate from endometrial cancer was .4 in the 10-year study. It was .2% amongst the five-year group.

Tamoxifen vs. Aromatase Inhibitors

  • A new class of drugs, aromatase inhibitors, has been approved for patients with early-stage ER-positive breast cancer since the ATLAS study started. This class of drugs has been shown to be more effective than tamoxifen in a five-year sample. It is currently the preferred treatment plan for patients with early-stage ER-positive breast cancer.
  • Long-term studies (10-year period) are underway to determine the effectiveness of aromatase inhibitors compared to tamoxifen.
  • Aromatase inhibitors are still under patent protection. They are considerably more expensive than tamoxifen and can cost thousands of dollars a month.
  • According to Susan G. Komen for the Cure the generic cost for tamoxifen is about $100 per month in the US.


The recent results from ATLAS during the San Antonio Breast Cancer Symposium must be confirmed with a meta-analysis of other extended tamoxifen studies (NSABP B-14 and others). Side effects from tamoxifen may include hot flashes; vaginal dryness, discharge or irritation; and a decreased interest in sex. Additional side effects, while rare, are more serious.

It is very important to speak to a doctor to fully understand the benefits and risks of tamoxifen before being prescribed.