Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information were in women without history of VPA use. Mean age at diagnosis of the cohort was 61 .8 years; mean years of prescription drug coverage was 7.4 years. Among cases, 73% of the cohort was non-hispanic white, 7.6% were African American, and 10.5% were Asian/Pacific Islander. When compared to never users, patients with at least 2 years of VPA use had an increased odds of a breast cancer diagnosis (OR 1.37; 95% Cl 1.06-1.76). This effect was only significant for HR-positive incident tumors, although the numbers of HR-negative cases was small (n=12) . These findings support that VPA use is not associated with reduction of breast cancer incidence. Moreover, we cannot exclude the possibility that VPA may be associated with a small but increased risk of HR-positive breast cancer. HDAC inhibition does not appear to be an effective or tractable strategy for breast cancer prevention .4

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