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No Changes in Breast Density Seen in Response to Treatment With Letrozole (Femara): Presented at SABCS

By Cameron Johnston

SAN ANTONIO, TX -- December 13, 2005 -- Women receiving letrozole (Femara) as endocrine therapy following tamoxifen therapy to prevent breast cancer recurrence do not seem to experience any significant loss in breast density as seen on mammograms.

This is contrary to what has been seen previously among women who were being treated with tamoxifen.

In a pilot study discussed this week here at the 28^th Annual San Antonio Breast Cancer Symposium (SABCS), investigators from Mayo Clinic in Rochester, Minnesota, and Princess Margaret Hospital in Toronto, Ontario, Canada, reviewed mammograms of women who had been enrolled in the National Cancer Institute of Canada - Cancer Trials Group MA.17 study. Women in that study had completed 5 years of tamoxifen therapy and were randomized to receive either placebo or letrozole.

According to principal investigator Celine M. Vachon, PhD, assistant professor of epidemiology, Mayo Clinic College of Medicine, past studies have shown that breasts with greater density have a 3- to 6-fold higher risk of breast cancer compared with less dense breasts. Also, tamoxifen has been shown to lessen breast density, while around 30% of women using hormone replacement therapies experience an increase in breast density.

Therefore, the researchers conducted their study to measure breast density before and after treatment with the aromatase inhibitor letrozole. Such changes in breast density could be indicative of changes in underlying hormonal status, or growth factors.

Women in the study were required to have one intact breast (those with bilateral breast cancer were excluded) and complete mammograms before randomization as well as during treatment. There were 48 women in the placebo arm and 57 in the letrozole arm.

Prerandomization and follow-up mammograms were used to estimate percent mammographic density and absolute density. From medical records, the researchers obtained data on patients' age, weight, and height at each mammogram, tumor stage, and nodal involvement.

On average women on letrozole had a 1.1% decrease in absolute percent density at 9 to 15 months of follow-up, while women on placebo had no change. Women on letrozole also experienced a minor, and nonsignificant change in absolute density compared with placebo.

From their first baseline mammogram to the 9 to 15 month evaluation, women on letrozole experienced a nonsignificant 5.3% decrease percent density. Breast absolute density also decreased by 6.0%. Neither of these changes was statistically significant.

By comparison, women receiving placebo had a nonsignificant increase in density of 3.2% and a nonsignificant increase in density area of 3.8%.

Overall, this means there was an annual decrease in breast density of 0.5%, which was not significant. The fact that the difference was not statistically significant could be due to the small sample size, Dr. Vachon said.

The authors concluded that using letrozole does not affect mammographic breast density or absolute density more than placebo. They noted, however, that these women might already have experienced some loss of breast density because they had been on tamoxifen therapy for a mean of 5 years before being enrolled in the MA.17 study.

Larger trials are needed to more fully understand the significance of changes in breast density, they said.

Given that breast density is associated with an increased risk of cancer, these findings suggest that women whose breasts have not lost any density should be followed more closely because cancerous tumors would be more difficult to detect even with regular mammography.


[Presentation title: Pilot Study of Changes in Mammographic Density in Women Treated With Letrozole or Placebo on NCIC CTG MA17. Abstract 6005]

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