Does Hormone Replacement Therapy Increase Breast Cancer Risk?

Hormone replacement therapy (HRT) was widely prescribed starting in the 1960s to alleviate menopausal symptoms like hot flashes, poor sleep and mood swings, but the narrative changed in the early 2000s after a large study indicated that HRT increased the risk of breast cancer, stroke and blood clots in women over 60.

For many women, that message stuck. But continued research and an evolving field today means a more nuanced approach to HRT and different options for women that can provide relief for symptoms without increasing breast cancer risk. (In fact, some research shows a decreased risk.)

The long-term national study called the Women’s Health Initiative (WHI) looked at women who were taking a specific combination of equine estrogen (derived from horse urine) and a synthetic progestin. Fast forward to now, and most providers use much lower doses and more natural, “bioidentical” hormones that more closely match the ones your body produces. For example, many doctors now prescribe estradiol, a plant-based form of estrogen, and micronized progesterone, which is considered safer than the older synthetic versions.

After re-analyzing older WHI data and combining it with newer data, the research consistently shows that natural HRT is beneficial in reducing mortality, coronary heart disease and osteoporosis, without causing a higher risk of breast cancer.

Newer research also clarifies some points. For example, the 20-year follow-up to the WHI study found that estrogen-only HRT lowered breast cancer risk in women with prior hysterectomies in all age groups. It also found that women aged 50 to 59 had a lower breast cancer risk compared to 60 and older.

Short-term combined HRT use (five years or less) starting at age 55 increases the risk of breast cancer by just 0.6%, and using HRT for 10 years adds another 1.8% risk. For comparison, having one drink a day increase the risk of breast cancer by 7%.

Deciding to take HRT is not always a black and white decision and can depend on a combination of factors:

•    Which hormones you take. Low-dose estrogen only is used for women who have had a hysterectomy. If you have a uterus, estrogen-only therapy can increase the risk of endometrial cancer. The combination of estrogen and progesterone actually reduces risk of endometrial cancer.
•    The method. Depending on your symptoms and situation, options include pill, patch, gel, cream, spray, and injection.
•    Age and time.  A recent study found that using HRT within 10 years of menopause carried more benefit that risk. 
•    Breast cancer history. HRT is not recommended for women who have or had breast cancer with a hormone-receptor positive subtype.

These are good points to consider for a jumping-off point with your doctor about risks vs. benefits, your specific symptoms and what the best plan is for you.