1001 Background: Arzoxifene (ARZ) is a third generation SERM with efficacy in metastatic breast cancer but lacking uterine agonist activity.
METHODS
We conducted a randomized, double-blind, placebo-controlled Phase II prevention trial in 199 high risk women assessing the effects of ARZ 20 mg/day on several risk biomarkers. Biomarkers, including cytomorphology of breast epithelial cells obtained by random periareolar FNA (RPFNA) were assessed at baseline and following 6 months of placebo or ARZ. Subjects were stratified by presence or absence of atypia, ER expression, BRCA1/2 mutation, as well as menopause status.
RESULTS
At entry, mean age was 47, 52% were premenopausal and 47% of postmenopausal women were taking HRT. Mean 10 year Gail was 6.8% and mean Masood cytology index score was 14.3. The ARZ and placebo groups were well matched. The protocol defined primary endpoint was a decrease in RPFNA cytology Masood index score by ≥3 points at 6 months and required 160 evaluable subjects for 81% power to detect a change from 30% to 52% of subjects showing improvement. For the 181 evaluable subjects, there was no significant difference in the proportion of women achieving ≥3 point improvement (19% placebo vs. 24% ARZ, p=0.46); or in change in mean index score (0.6 placebo vs. 0.9 ARZ, p=0.53). There was also no difference in grade 3 or 4 side effects or dropout prior to 6 months. However, comparing ARZ to placebo, there was favorable modulation of the two risk biomarkers, mammographic breast density (p=0.001) and IGF-1:IGFBP-3 ratio (p=0.001), and reduction in bone turnover biomarker osteocalcin (p= 0.002), but without an increase in endometrial thickness.
CONCLUSIONS
Although improvement in cytomorphology after 6 months of ARZ was not shown, the acceptable side effect profile and favorable modulation of other biomarkers (breast density, IGF-1:IGFBP-3, osteocalcin) provides support for continued evaluation of ARZ as a breast cancer prevention agent. No significant financial relationships to disclose.