TUESDAY, May 27, 2014 (HealthDay News) — The hormone-blocking medication tamoxifen should be given for as long as 10 years following treatment of certain types of breast cancer, according to updated guidelines from the American Society of Clinical Oncology (ASCO).

“Tamoxifen taken for five years has been the standard . . . but we now have evidence to recommend up to 10 years of tamoxifen for women with hormone receptor-positive breast cancer,” guideline update panel co-chair Dr. Harold Burstein said in an ASCO news release.

The new guidelines include women with hormone receptor-positive breast cancers between stage 1 and stage 3.

Hormone receptor-positive breast cancer is a type of cancer that is fueled by certain hormones, often estrogen. Hormone receptor-positive breast cancer is the most common type of breast cancer worldwide, according to the ASCO news release.

Tamoxifen blocks the ability of cancer cells to use estrogen, according to the U.S. National Cancer Institute.

The latest recommendation on tamoxifen treatment is based on new data from five studies reviewed since the society’s previous update in 2010.

In the two largest studies with the longest follow-up, patients who took tamoxifen for 10 years after initial treatment survived longer than women who took the drug for five years. Additionally, women who took tamoxifen for 10 years were less likely to have their breast cancer come back, or to develop cancer in the other breast, compared with those who took tamoxifen for five years.

The updated guideline, published online May 27 in the Journal of Clinical Oncology, also addresses issues doctors face when talking with patients about taking this type of therapy — known as “adjuvant endocrine therapy” — for long periods of time.

“It is important for clinicians and patients to discuss the trade-offs between potential risks of side effects and potential benefits of taking adjuvant endocrine therapy for up to 10 years,” guideline update panel co-chair Dr. Jennifer Griggs said in the news release.

“Many women taking adjuvant tamoxifen experience side effects, and these appear to persist with longer duration. However, the trials did not find any new or unexpected side effects,” she noted.

More information

The U.S. National Cancer Institute has more about hormonal therapy for breast cancer.