Breast Cancer and Hormone Therapy: An Evolving Relationship

Menopausal hormone therapy effects on breast cancer risk may vary over time

/ Author:  / Reviewed by: Robert Carlson, M.D Beth Bolt, RPh

(RxWiki News) When it comes to breast cancer risk, not all hormone therapies are created equal. While some may continue to increase the risk of cancer years after a patient stops taking the medications, others can decrease the odds of getting the disease.

The way menopausal hormone therapy affects breast cancer risk may change year to year, including long after a patient stops hormone use, according to a recent study that used data from two trials of postmenopausal women.

"The use of menopausal hormone therapy (HT) continues in clinical practice, but reports are conflicting concerning the longer-term breast cancer effects of relatively short-term use," wrote the authors of this study, led by Rowan T. Chlebowski, MD, PhD, of the Los Angeles Biomedical Research Institute.

Dr. Chlebowski and team reviewed early and long-term effects of hormone therapy on breast cancer in more than 27,000 women aged 50 to 79. The women, who had no past breast cancer, took part in two clinical trials between 1993 and 1998. Almost 17,000 of them still had a uterus and received a combined therapy of estrogen and progesterone or a placebo (fake treatment). The rest of the patients, whose uteri had been removed, received only estrogen or placebo.

The research team followed the effects of the hormone therapies over 13 years. With combined therapy, the risk of breast cancer was high during the treatment but dropped dramatically within two years of stopping the treatment. However, the risk of cancer in those patients remained high years later, Dr. Chlebowski and team found.

Estrogen appeared to reduce the risk of breast cancer during the therapy and kept it low in the years immediately after the treatment stopped. However, the risk was not as low later in the follow-up, Dr. Chlebowski and team found.

"The ongoing influences on breast cancer after stopping hormone therapy ... require recalibration of breast cancer risk and benefit calculation for both regimens, with greater adverse influence for estrogen and progestin use and somewhat greater benefit for use of estrogen alone," Dr. Chlebowski and team wrote.

Menopausal hormone therapy is prescribed to relieve common symptoms of menopause and to address biological changes like bone loss. A woman whose uterus has been removed is usually prescribed estrogen alone. Patients who have not had this surgery may receive estrogen and progesterone or estrogen and progestin, a synthetic hormone with effects similar to those of progesterone. The National Cancer Institute tells women to use hormone therapy for the shortest time possible, and in the lowest dose, due to a possible increased risk of cancer.

Rama Khokha, PhD, of the Princess Margaret Cancer Centre in Toronto, Canada, said doctors should rethink progesterone therapy, given the increased risk of cancer seen with long-term use.

"Emerging detailed analyses ... such as that reported by Chlebowski et al reveal new compelling evidence for the significance of progesterone in breast cancer, where it has traditionally taken a backseat to estrogen," Dr. Khokha wrote in an editorial about this study.

The study and editorial were published April 16 in JAMA Oncology.

The National Heart, Lung and Blood Institute funded the clinical trials. Dr. Chlebowski received funds from AstraZeneca, Novartis, Amgen, Genomic Health and Novo Nordisk.

Review Date: 
April 16, 2015
Last Updated:
April 20, 2015