P2-08-01: Impact of Aromatase Inhibitors on Background Parenchymal Enhancement and Amount of Fibroglandular Tissue on Breast MRI.

Abstract

Abstract Background: On breast MRI, background parenchymal enhancement (BPE) and volume of fibroglandular tissue (FGT) have been shown to reflect a patient's hormonal status. Tamoxifen has been shown to reduce mammographic breast density and may serve as an early predictor of response in the prevention setting (Cuzick, JNCI 2011). We have shown that adjuvant tamoxifen can reduce BPE in the unaffected breast in women with breast cancer. We hypothesize that aromatase inhibitor (AI) induced endocrine changes in breast tissue should also be evident and therefore we performed a study to evaluate whether adjuvant AI therapy influences BPE or amount of FGT in the contralateral breast. Methods: An electronic medical record review identified 856 postmenopausal women with stage I-III breast cancer who had at least two breast MRIs and took adjuvant AI treatment. A retrospective chart review was conducted to select those patients without a history of prior tamoxifen or raloxifene treatment who had a MRI of the contralateral breast both before and during 6 to 12 months of AI treatment. After exclusion of all irradiated breasts, 168 women were eligible. MRIs were performed between August 1999 and June 2010. Two radiologists who were blind to AI treatment status, independently rated level of BPE and amount of FGT using categorical scales: BPE — Minimal, Mild, Moderate, Marked; FGT — Fatty, Scattered, Heterogeneously Dense, Dense (based on proposed BIRADS criteria for BPE and on ACR criteria for FGT). Blinded side-by-side direct comparison evaluated whether there was a category change between the two MRIs. A consensus was reached in cases of disagreement. The Wilcoxon signed-rank test was used to assess changes in rating categories for BPE and FGT between before and during AI breast MRIs. A waiver of authorization was granted by the institutional review board for this study. Results: In this study 127/168 (76%) women were treated with anastrozole, 33/168 (20%) with letrozole and 8/168 (5%) with exemestane. Based on the blinded side-by-side comparison, a category (or more) decrease in BPE occurred during treatment with AIs (p<0.0001). There was an overall shift from higher to lower degree of BPE in 35% (45/127) of the women taking anastrozole while a category increase occurred in only one woman (1%; p <0.0001). A similar result was seen in the women taking letrozole [45% (15/33) had a decrease versus 3% (1/33) an increase; p=0.0003] and exemestane [25% (2/8) had a decrease versus 12.5% (1/8) an increase; p=0.50]. For FGT a category decrease occurred in 5% (6/127) of anastrozole users while no increase occurred [0% (0/127), p=0.016]. The respective numbers for letrozole were 3% (1/33) and 0% (0/33), and nobody on exemestane had a change in FGT. Conclusions: After 6 to 12 months of treatment with adjuvant AIs, there was a statistically significant category (or more) decrease in BPE. BPE is more sensitive than FGT to changes in normal breast stroma that occur during adjuvant treatment with AIs and BPE may be a marker of anti-hormonal activity in the breasts. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-08-01.