In a five-year review of 20 clinical trials, tamoxifen was shown to safely reduce both 15-year risk for recurrence and death in early-stage estrogen receptor-positive breast cancer.
Researchers from the Clinical Trial Service Unit in Oxford, England, reviewed studies that spanned more than 20 years to consider the effects of tamoxifen related to hormone receptor levels, age, use of chemotherapy and other factors.
Background on Tamoxifen in Early-Stage Breast Cancer
Tamoxifen is the oldest and most studied medicine for blocking the effects of estrogen in breast tissue. It is used for prevention in healthy women and for women with all stages of breast cancer. In hormone receptor-positive, early-stage breast cancer, it is given to reduce the risk of the cancer coming back after surgery.
Since its approval for this use by the U.S. Food and Drug Administration, tamoxifen has been widely used to treat ER-positive breast cancer. It is the standard treatment for premenopausal women, and can also be prescribed for postmenopausal women.
When tamoxifen is metabolized, or absorbed into your body, it is changed at a certain point into another substance called endoxifen, a powerful anti-estrogen agent that is active in preventing the growth of cancer cells.
Previous research shows tamoxifen can reduce the risk of breast cancer returning by 30 to 50 percent. It has also been shown to reduce the risk of a new cancer developing in the other, healthy breast by about 50 percent.
In this review, the researchers pooled findings from similar studies to see whether the lessened risk for recurrence translates into longer overall survival. They also investigated whether women receive benefit from tamoxifen beyond their years in treatment.
Structure of the Review
The review included data from clinical trials of 21,457 women with early ER positive breast cancer. About half the participants received approximately five years of tamoxifen treatment; the remainder did not. Clinical trials that included women with DCIS (ductal carcinoma in situ or non-invasive breast cancer) were excluded.
Among women treated with tamoxifen, the reviewers found recurrence rates were substantially reduced for the first 10 years after starting treatment. Recurrence rates remained steady in years 10-14. Compared to women who did not take tamoxifen, women who received it had a reduced risk of death from breast cancer by about one-third through the first 15 years from diagnosis. These trends remained consistent, despite differences in tumor size and the cancer’s sensitivity to estrogen.
Rate of recurrence was not related to progesterone levels, lymph node status or age at diagnosis, the reviewers found. They concluded that tamoxifen’s effect in reducing risk of recurrence was independent of these factors. This suggests that it was tamoxifen that positively impacted recurrence and risk of death. In addition, recurrence and death rates remained the same, whether tamoxifen was used during or after chemotherapy, keeping in mind that standard practice is for tamoxifen to be given after chemotherapy is finished. This suggests that tamoxifen’s effect was independent of other treatment measures.
What This Means for You
These findings reinforce previous studies that show tamoxifen significantly reduces the potential for recurrence and decreases risk of death in early ER-positive breast cancer. The findings also showed that the impact of tamoxifen on both recurrence and mortality was independent of other factors, including its use as an adjuvant therapy. If tamoxifen is or has been part of your treatment plan, these findings may reassure you about the protection this medicine affords you during treatment and in the years after.