Many women who follow initial breast cancer treatment with five years of hormone therapy to keep tumors at bay may still experience new malignancies up to two decades after their diagnosis, a study suggests. Researchers examined data from 88 clinical trials involving 62,923 women with estrogen receptor (ER)-positive tumors. After treating ER-positive tumors with chemotherapy, radiation or surgery, women typically get five years of follow-up therapy with daily hormone-based pills - either tamoxifen or aromatase inhibitors.
The goal of the adjuvant therapy is to destroy any lingering cancer cells not killed by initial treatment. All of the women were cancer-free when they completed five years of adjuvant hormone-based therapy. During the next 15 years, however, cancer returned for 41% of the highest-risk women in the study who originally had the largest tumors that had spread the most beyond the breast, the study found.
Even the lowest-risk women who originally had small tumors that hadn't spread to the lymph nodes or other parts of the body still had 10% odds of cancer coming back during the study, researchers report online November 13 in the New England Journal of Medicine. "We know that adjuvant (hormone-based) therapy for 5 years substantially reduces the risk of recurrence and mortality," said senior study author Dr. Daniel Hayes of the University of Michigan Comprehensive Cancer Center in Ann Arbor.
"We now have good evidence that extending adjuvant (hormone-based) therapy beyond five years continues to suppress and reduce recurrence and mortality," Hayes said by email. Doctors have long known that five years of tamoxifen reduces recurrence by approximately half during treatment, and by nearly a third over the next five years. Aromatase inhibitors, which work only in post-menopausal women, are even more effective than tamoxifen at reducing recurrence and death from breast cancer.
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