New Canadian Study to Evaluate Cancer Agent in Women at Increased Risk of Breast Cancer


One in nine Canadian women is expected to develop breast cancer in her lifetime and this year alone an estimated 20,500 women will be diagnosed with breast cancer, and 5,400 will die of it. These alarming statistics are the driving force behind a new breast cancer prevention study that will examine the effectiveness of the anti-aromatase agent exemestane (AROMASIN(r)) in healthy postmenopausal women with increased mammographic breast density.

Paul Goss, MD, PhD, Professor of Medicine, University of Toronto, Princess Margaret Hospital, is leading the year-long study by the National Cancer Institute of Canada Clinical Trials Group (NCIC-CTG) in collaboration with Canadian and U.S. investigators. “Research shows that approximately 30 per cent of breast cancer cases may be attributed to radiologically dense tissue in more than 50 per cent of the breast. This study will examine if one year of treatment with exemestane, compared to placebo, leads to a decrease in breast density and potentially, a decreased risk of developing breast cancer,” says Dr. Goss.

Breast cancer is the most frequently diagnosed cancer in Canadian women and is currently the leading cause of all cancer deaths amongst women between the ages of 30 and 49. Although breast density decreases with age; it may increase in women who use hormone replacement therapy or who have a family history of breast cancer. This relationship suggests that female hormones such as estrogen are responsible for changes in breast tissue. Anti-aromatase agents such as exemestane reduce the production of menopausal estrogens, thereby halting the supply of these hormones to pre-cancerous and cancerous cells, which in turn prevents them from continuing to grow. “An increased pattern in density may signify changes in breast tissue associated with an increased risk of developing cancer,” Dr. Goss adds. “With this important study, we hope to learn more about treatments that can help prevent the onset of cancer, as well as offer protection against other potential health problems linked to menopause.”

In addition to increasing age and family history of breast cancer, other risk factors include 3:

  • a history of breast cancer in one breast;
  • a history of certain types of benign breast disease;
  • high levels of radiation exposure to the chest;
  • obesity in postmenopausal women;
  • never having had children;
  • being 30 or more years of age at first full-term pregnancy;
  • having an early onset of menstruation; and
  • having a late onset of menopause.

The double blind, randomized trial will involve approximately 120 women in five Canadian and 12 U.S. sites. To participate, the women must be postmenopausal with baseline mammograms that indicate an increased radiological density occupying > 25 percent of breast tissue. During the study, participants will be randomized to receive either exemestane 25 mg once daily or placebo, and will be evaluated after one year to determine if the treatment has shown a reduction in breast density by at least > 1 grade. One year later, a second analysis of this group will be conducted to measure whether this effect is sustained over time. In addition, the study will evaluate the potential of exemestane to improve bone and lipid metabolism, and its possible side effects.

“Our goal is to find and test better ways to treat and prevent cancer through clinical trials,” says Dr. Joseph Pater, Director of the National Cancer Institute of Canada Clinical Trials Group. “This study represents an important step on the path to reducing the number of patients who develop breast cancer,” he adds.

At present, the only proven strategy to reduce breast cancer deaths is early detection. There is evidence that demonstrates screening mammography can reduce mortality from breast cancer by approximately 30 percent in women aged 50-69.

“Breast cancer is a major public health issue and there are still many questions that remain unanswered,” says Dr. Goss. “However, studies such as this one will provide long-term data in healthy women and will help to differentiate anti-aromatase agents, in terms of their efficacy in the treatment of breast cancer and their effects on end organs.”