Study: Breast cancer risk lasts for decades

Recurrence in 41 percent of high-risk women

Many women who follow initial breast cancer treatment with five years of hormone therapy to keep tumors at bay might 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 what’s known as estrogen receptor-positive tumors, a common type of breast cancer that responds to hormone-based treatments.

After treating ER-positive tumors with chemotherapy, radiation or surgery, women typically get five years of follow-up therapy in the form of daily hormone-based pills, either tamoxifen or aromatase inhibitors. The goal of such so-called 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 percent 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 percent odds of cancer coming back during the study, researchers report in the New England Journal of Medicine.

“We know that adjuvant (hormone-based) therapy for five 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.