For women with hormone receptor-positive breast cancer – the most common type of breast cancer worldwide – the American Society of Clinical Oncology (ASCO) is now recommending a decade of follow-up care with tamoxifen.
The update to the ASCO guidelines, announced today, reflects the findings of five studies that have been reported since the last update to the recommendation in 2010. In the two largest randomized studies with the longest follow-up, women who took tamoxifen for 10 years had a survival advantage compared to those who took the drug for five years. In addition, women who took the drug longer had a lower risk of breast cancer recurrence and of breast cancer appearing in their other breast.
A five-year regimen of tamoxifen had been the standard treatment, but because of the growing body of research pointing to a benefit in a longer course, many doctors already had recommended a decade-long regimen for their patients.
“This is something we’ve been doing here at City of Hope for at least the last year or so,” said Courtney Vito, M.D., a staff surgeon and surgical oncologist. “I think that it is important to note that even with early stage breast cancer, there is a risk of relapse and what we’re learning is estrogen receptor-positive breast cancer can relapse as many as 20 years out.”
Most breast cancers fall into the hormone receptor-positive category, with about 60 to 75 percent of breast cancer patients being diagnosed with estrogen receptor-positive breast cancer. About 65 percent of these cancers are also progesterone receptor-positive.
In estrogen receptor-positive breast cancer, estrogen promotes the growth of cancer cells. Tamoxifen blocks the effect of estrogen on cancer cells, slowing or stopping the growth of cancer cells already in the body. It’s the most common hormone therapy for treating breast cancer.
The most common side effects of the drug are hot flashes, vaginal dryness, irritation or discharge, and reduced libido. More serious potential side effects include an increased risk of blood clots in the legs, and a small increased risk of stroke, ovarian cysts, uterine cancer and endometrial hyperplasia – an overgrowth of the uterine lining.
“This is not a drug that is without side effects, both from quality-of-life standpoint as well as from the standpoint of medical risks,” Vito said. “There are rare, but real, risks of developing an endometrial cancer or blood clots in the legs such as a [deep vein thrombosis] or a clot that can embolize and go to the lungs. These are serious, but also rare.”
The updated recommendations include these guidelines for doctors treating breast cancer:
Vito said patients need to be aware of the trade-offs between tolerating side effects and reducing the risk of cancer. Stopping therapy sooner now shows an increased risk of a breast cancer recurrence, and a potential increased risk of death from breast cancer.
“In my opinion, once you balance all of these risks and benefits, there is a benefit for extending therapy for 10 years, and it is an achievable goal in many cases,” Vito said. “If I can offer my patient a better cure for her breast cancer and a more durable cure, I think that’s worth investing in.”
Learn more about breast cancer treatment and research at City of Hope.