Even though I had estrogen-negative (ER-) breast cancer, my oncologist was insistent that I take tamoxifen. I refused. And I changed oncologists. The research below supports my decision.
Women who took tamoxifen for at least five years had more than a four-fold increased risk of estrogen-receptor negative cancer in the second breast compared to women who were not treated with hormone therapy, according to research published in the journal Cancer Research.
The drug reduced the incidence of estrogen-receptor-positive breast cancer by 60 percent, however.
Researchers studied 367 women with estrogen-receptor-positive cancer that had also spread to the second cancer. The comparison group was 728 women with only a primary cancer.
• breast cancer survivors overall who took hormonal therapy were at a reduced risk of second breast cancer.
• use of tamoxifen for at least five years reduced the risk of both estrogen-positive and progesterone-positive breast cancer.
• use of the drug for at least five years led to increased risk of both estrogen-negative and progesterone-negative.
Researchers said that the reason the risk increases with longer exposure is because more time is needed “to foster an environment that promotes estrogen receptor-negative tumor growth.” Essentially, they said, hormone therapy gives hormone–negative cells a growth advantage.
SOURCE: Li, Christopher I., Daling, Janet R., Porter, Peggy L., Tang, Mei-Tzu C., Malone, Kathleen E., “Adjuvant Hormonal Therapy for Breast Cancer and Risk of Hormone Receptor-Specific Subtypes of Contralateral Breast Cancer,” Cancer Research, 2009 0: 0008-5472.CAN-09-1355. Published online August 25, 2009.