Tamoxifen and Zoladex (chemical name: goserelin) are hormonal therapy medicines used to lower the risk of breast cancer coming back (recurrence) in premenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer. A study found that tamoxifen and Zoladex work about the same to lower the risk of breast cancer coming back.
Estrogen can make hormone-receptor-positive breast cancers grow. Hormonal therapy medicines treat hormone-receptor-positive breast cancers in two ways:
- by blocking the action of estrogen in the body
- by lowering the amount of estrogen in the body
There are several types of hormonal therapy medicines. Zoladex is a luteinizing hormone-releasing hormone (LHRH) agonist. Zoladex works by stopping the ovaries from making estrogen. Doctors may refer to this as "medical ovarian shutdown." Zoladex is given by injection every 4 weeks. Tamoxifen is a selective estrogen receptor modulator (SERM). Tamoxifen works by blocking the effects of estrogen in breast tissue, including hormone-receptor-positive breast cancers. Tamoxifen is a pill taken by mouth once a day.
More than 2,700 women diagnosed with hormone-receptor-positive breast cancer participated in the ZIPP (Zoladex In Premenopausal Patients) trial. After surgery and other treatments, the women got 1 of 4 treatment approaches to reduce the risk of breast cancer recurrence:
- tamoxifen alone for 2 years
- Zoladex alone for 2 years
- tamoxifen and Zoladex in combination for 2 years
- no additional treatment
The women were followed for more than 10 years. The results:
Tamoxifen and Zoladex worked about the same to lower the risk of breast cancer coming and improve survival. Compared to women who didn't get either medicine, the risk of breast cancer coming back was 33% lower for women who got 2 years of Zoladex and 29% lower for women who got 2 years of tamoxifen. The difference in recurrence risk reduction between the two medicines wasn't significant, which means it could have been due to chance.
There was no difference in the risk of breast cancer coming back between women who got BOTH tamoxifen and Zoladex and women who got ONLY tamoxifen or ONLY Zoladex. This finding is important because doctors often recommend the medicines be used together to reduce the risk of recurrence.
Zoladex may cause bones to weaken. In this study, researchers looked at a smaller group of 89 women to see if there were any differences in bone strength between the treatment groups. Women who got Zoladex had a 5% reduction in bone mineral density, which means their bones were weaker. Bone mineral density went up after the women stopped taking Zoladex. Women who got both tamoxifen and Zoladex had a 1.4% reduction in bone mineral density. The difference in bone mineral density reduction is likely due to tamoxifen. Tamoxifen can actually strengthen bones in many women.
If you're premenopausal and have been diagnosed with hormone-receptor-positive early-stage breast cancer, you and your doctor will discuss many treatment options to lower the risk of breast cancer coming back after surgery. Hormonal therapy will be one of these options. The study reviewed here shows that either tamoxifen alone or Zoladex alone can be a good option.
For some women with very high risk of the cancer coming back or of a new, second breast cancer, surgically removing the ovaries is another option.
Before you decide on a treatment plan, be sure to talk about all the benefits, side effects, and risks of each option with your doctor. Together you can make the best decision for you and your unique situation.
Visit the Breastcancer.org Hormonal Therapy section to learn more about all the hormonal therapy medicines that can be used to treat breast cancer and lower the risk of it coming back.