Antihormonal medications influence parenchymal enhancement differently

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The effects of tamoxifen and aromatase inhibitors, two antihormonal medications, differ on benign parenchymal enhancement in breast MRI, according to a study published in the April issue of Radiology.

Antihormonal therapy that is targeted to the estrogen receptor is widely considered to be one of the most vital components of breast cancer treatment. Tamoxifen has shown improvement in disease-free survival and overall survival in premenopausal and postmenopausal women, while aromatase inhibitors have been established for use in the postmenopausal demographic. Postmenopausal women who have hormone receptor-positive breast cancer often receive an aromatase inhibitor as up-front therapy or sequential treatment after tamoxifen, explained lead author Simone Schrading, MD, of the University of Aachen in Germany, and colleagues.

Moreover, the degree of background enhancement in dynamic-contrast enhanced breast MRI has demonstrated a strong correlation to the hormonal stimulation levels of the breast. Though recent studies have revealed that background enhancement on breast MRI decreases with tamoxifen therapy and aromatase inhibitors, research is lacking on the effects of the two antiestrogenic medications on the glandular tissue.

Schrading and colleagues conducted a prospective intraindividual longitudinal cohort study to compare the effects of the two medications. The study included 40 postmenopausal women with unilateral breast cancer. All women underwent breast MRI before starting any medication, while taking tamoxifen and after switching to an aromatase inhibitor.

Prior to treatment, the distribution of background enhancement MR-American College of Radiology categories one, two, three and four was 20 percent, 35 percent, 33 percent and 13 percent, respectively. Background enhancement was suppressed with tamoxifen, as distribution was 80 percent, 15 percent, 5 percent, 23 percent and 0 percent for the categories.

Background enhancement rates were highest before treatment in all 40 women with a mean of 51.3 percent. When tamoxifen was used, background enhancement rates significantly reduced to a mean of 8.4 percent and then increased after the switch to an aromatase inhibitor with a mean of 22.9 percent. The prevalence of benign enhancing foci was 65 percent at baseline, 12.5 percent with tamoxifen and 40 percent with an aromatase inhibitor.

“Because tamoxifen and aromatase inhibitors appear to have equivalent clinical efficacy, we speculate that the effects of tamoxifen that are observable via MR images should in part be because of other antiangiogenic effects,” wrote the researchers. “The difference between the effects of tamoxifen and aromatase inhibitors should be considered when MR examinations of patients who are using tamoxifen or AI aromatase inhibitors are interpreted. Finally, MR imaging could be useful to identify patients who are so-called poor metabolizers of tamoxifen.”