HRT and Breast Cancer: What Nurses and Patients Should Know

By Emily Menendez - Last Updated: December 22, 2022

Since the introduction of hormone replacement therapy 70 years ago, the use of HRT among post-menopausal women has been well-documented, with 44% of postmenopausal women reporting using HRT in a study from 1988 to 1994. In 2000, 46 million prescriptions were written for the medication Premarin (conjugated estrogens) in the United States alone, making it the second most frequently prescribed drug in the country. Approximately 600 million women in western countries report having used HRT at some point in their lives. 

Potential Risks of HRT 

While HRT treatments can relieve postmenopausal symptoms, long-term use of HRT has been linked to an increased risk of developing breast cancer, causing skepticism in some women who consider taking HRT. Therefore, when patients are considering HRT, physicians and nurses should engage in constructive discussions regarding HRT while going over potential risks of its use and provide alternatives if the need arises. 

A common HRT treatment involves conjugated estrogens on their own or combined with progestin to prevent cardiovascular disease and cognitive deficits in post-menopausal women, as well as reduce vasomotor symptoms. However, several clinical studies have found a higher rate of breast cancer incidence and mortality among those who use HRT. Estradiol has been found to increase the risk of breast cancer in post-menopausal women and can also bring on the occurrence of progenitor cells in both human and breast cancer cells. HRT-induced blood estrogen levels can also cause in increased incidence of estrogen receptor-positive breast cancer, especially in women with higher body mass index.  

WHI Studies on HRT 

The Women’s Health Initiative (WHI) carried out a landmark study in 2002 that examined the benefits and complications inherent in HRT treatment. The study was comprised of 16,608 healthy post-menopausal women who underwent treatment with conjugated equine estrogens and medroxyprogesterone acetate or placebo for a median duration of 7.2 years. The group that was given HRT was associated with a higher rate of breast cancer-related deaths compared to the placebo group, causing the clinical trial to be terminated. 

The WHI again assessed the negative outcomes of HRT in 2004, when they evaluated 10,739 post-menopausal women between the ages of 50 and 79 years old who had a prior hysterectomy who had been prescribed either conjugated equine estrogens or placebo. This study was also terminated prematurely due to an elevated risk of stroke in the HRT group. However, the results suggested a potential decrease in the incidence of breast cancer. 

Several studies have noted that estrogen alone may be safe, but estrogen and progesterone together may post a detrimental or countervailing effect due to its association with an increased risk of breast cancer. Therefore, physicians and nurses should consider the potential effects of including the two agents as HRT treatments for patients before prescribing them. 


Hormone Therapy and Risk of Breast Cancer: Where Are We Now? 

Use of Hormone Replacement Therapy Among Postmenopausal Women in the United States, 1988–94 

Making Decisions About Hormone Replacement Therapy