Incident rate dropped sharply after patients stopped estrogen with progestin therapy

San Antonio Breast Cancer Symposium

SAN ANTONIO — Postmenopausal women participating in the Women’s Health Initiative saw their risk for breast cancer decrease rapidly after stopping estrogen with progestin therapy.

Rowan T. Chlebowski, MD, PhD, a medical oncologist with Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, presented the results at the CTRC-AACR San Antonio Breast Cancer Symposium.

Women assigned to hormone therapy in the WHI had a 26% increase in breast cancer incidence, he said. Chlebowski said the drop in incidence within six months of stopping hormone replacement therapy was linear and sharp.

“The increased breast cancer risk associated with combined estrogen and progestin use declined markedly after therapy discontinuation,” he said.

HR for the increase in risk was 1.26 — nearly identical to the HR of 1.27 found after researchers ordered patients to stop the therapy in July 2002.

“When we looked at the HRs every six months, you could see that the incidence was going up in a linear fashion. Post-intervention, it was going down in a linear fashion,” he said. “The HRs were the same because one was in the middle of going up and one was in the middle of going down.”

Chlebowski said that the final HR during the period of increasing incidence was 1.62.

He added that the data showed the decrease could not be attributed to a change in the number of mammograms performed. “The absolute difference in mammography did not change, so mammography cannot account for the change in breast cancer incidence seen,” he said.

Chlebowski said these findings only apply for women who have not had a hysterectomy and who were assigned to the combination therapy. Women who have had a hysterectomy can safely take estrogen alone. – by Jason Harris

For more information:

Chlebowski RT. #64. Presented at: the 31st Annual CTRC-AACR San Antonio Breast Cancer Symposium; Dec. 10-14, 2008; San Antonio.