Combined HRT Treatments, Longer Use, Linked To Increased Breast Cancer Risks: Study

A new study appears to add to the body of evidence that side effects of hormone replacement therapy (HRT) increase the risk of breast cancer for women, particularly when combined progestogens and following long durations of use.

Researchers from the United Kingdom say the breast cancer risk from HRT treatments may increase as much as 88% for some products, and could cause as many as 36 extra instances of breast cancer among women per 100,000 users.

In findings published last week in the medical journal The BMJ, researchers looked at data on more than 98,000 women between the ages of 50 and 79 with a primary diagnosis of breast cancer between 1998 and 2018, and compared them to data on more than 457,000 controls.

According to the findings, 34% of those with a diagnosis of breast cancer used HRT at least one year prior, compared to 31% of women who were not diagnosed with breast cancer. The researchers found recent and long term users of oestrogen only therapy and oestrogen and progestogen combination therapy had an overall increased risk of 15%.

However, those who used combined progestogens saw an 99% increased risk when they had used noresthisterone, the highest risk recorded. The lowest risk for a combined progestogen was dydrogesterone, which was linked to a 24% increased risk.

The researchers determined recent oestrogen-only users saw an extra three to eight women per 100,000 would be expected to develop breast cancer, with younger women associated with the lower number, and older women associated with the higher rate. Among oestrogen-progestogen users, that number increased to between nine and 36 extra cases of breast cancer per 100,000 women.

“This study has produced new genralisable estimates of the increased risks of breast cancer associated with use of different hormone replacement preparations in the UK,” the researchers concluded. “The levels of risk varied between types of HRT, with higher risks for combined treatments and for longer duration of use.”

This is only the latest study to link HRT use with breast cancer over the past two decades.

In 2002, a study by the Women’s Health Initiative first warned of the risk of breast cancer from hormone replacement therapy.

In 2012, a study using data from the Nurse’s Health Study, found an 88% increase in the risk of breast cancer for women who underwent HRT over a period of 10-15 years. The risk doubled if the women used HRT for 15 to 20 years.

The manufacturers of Prempro, Premarin and other HRT medications have faced thousands of breast cancer lawsuits filed by former users of hormone replacement therapy, which alleged that inadequate warnings were provided about the safety of the medications.

Pfizer agreed to pay out about $1.2 billion to settle 10,000 HRT breast cancer lawsuits in 2012.