Postmenopausal women with early-stage, hormone-sensitive breast cancer have a lower risk of disease recurrence when their treatment includes a new class of hormone therapy drugs, yet one out five women prescribed the drugs may not take them regularly, according to a study conducted by researchers at Dana-Farber Cancer Institute and AstraZeneca Pharmaceuticals. Their findings will be presented at the 29th annual San Antonio Breast Cancer Symposium on Saturday, Dec. 16 (Abstract 4044).

“These data are very concerning because hormonal therapy for breast cancer is one of the most effective treatments in all of oncology,” said Ann Partridge, MD, MPH, the study’s lead author and a breast cancer specialist at Dana-Farber. “Women may be compromising their care, and ultimately their survival, if they do not take these medications as recommended.”

Partridge and her colleagues analyzed claims data from three large commercial health plan systems to gauge treatment compliance of more than 7,000 women with early stage-breast cancer who, in addition to their regular treatment, began taking anastrozole.

Anastrozole is part of a new class of drugs, called aromatase inhibitors, that reduces the production of the hormone estrogen by blocking aromatase, an enzyme that converts the hormone androgen into estrogen. Studies have shown that lowering estrogen levels in post-menopausal women with hormone receptor-positive breast cancer can reduce their risk of disease recurrence.

In one of the health plans analyzed, the researchers found that 85 percent (1,275) of the women were still filling their prescriptions a year after anastrozole was first prescribed, but not everyone was doing so on a regular basis. The researchers also looked at the prescription filling habits of the 1,111 women who had been enrolled in the health plan for 12 consecutive months. They determined that, due to inconsistent refills, 19 percent of the women (211) had access to the drug less than 80 percent of the 12-month period after they first filled an anastrozole prescription. These women were considered to be non-adherent to the treatment.

“This study confirms that even patients with cancer may be non-adherent to their treatment,” said Partridge, who is also an assistant professor of medicine at Harvard Medical School. “Non-adherence is a very complex issue, and the reasons that a patient may not take her medication as directed can include fear of or the experience of side effects, cost of treatment, and negative health beliefs, like the treatment will not help.”

The study’s other authors are Andrea LaFountain, PhD, Brooke Taylor, PhD, and Aviva Asnis-Alibozek, PA-C, MPAS, of AstraZeneca.

The research was funded in part by AstraZeneca of Wilmington, Del. AstraZeneca markets anastrozole in the United States under the trade name Arimidex®.

Source: Dana-Farber Cancer Institute