Background: Breast cancer chemoprevention with selective estrogen receptor modulators (SERMs) and aromatase inhibitors (AIs) have been shown in randomized controlled trials to reduce breast cancer incidence by 50-65% among high-risk women. However, chemoprevention is still underutilized with fewer than 5% of high-risk women offered chemoprevention agreeing to take the medications. Reasons for low chemoprevention uptake include inadequate knowledge about chemoprevention among patients and healthcare providers, concerns about side effects, competing comorbidities, and time constraints during the clinical encounter. To address these barriers to chemoprevention uptake, we developed decision support tools for patients and providers. Methods: We conducted a randomized controlled trial of standard educational materials alone or combined with web-based decision support tools, RealRisks and BNAV, among 300 high-risk women and 50 healthcare providers, respectively. Patient eligibility criteria included: 1) women, age 35-75 years; 2) high-risk for breast cancer, defined as a 5-year invasive breast cancer risk ≥1.67% according to the Gail model or history of lobular carcinoma in situ (LCIS); 3) no prior use of a SERM or AI; 4) No personal history of breast cancer; 5) Access to the internet. Providers included primary care providers, such as internists, family practitioners, gynecologists, and nurse practitioners, and specialists, such as breast surgeons and medical oncologists. The RealRisks decision aid (DA) is available in English and Spanish and includes interactive modules to communicate personalized breast cancer risk and the risks and benefits of chemoprevention. The BNAV tool includes self-paced learning modules on breast cancer risk factors and chemoprevention and was made available to all providers through the electronic health record (EHR) dashboard. The primary endpoint was chemoprevention uptake at 6 months as assessed via the EHR. Secondary outcomes included validated measures of perceived breast cancer risk, breast cancer worry, chemoprevention knowledge, self-efficacy, decision conflict, chemoprevention attitudes, intention, and informed choice, which were administered to patients at baseline, 1 month, and 6 months after randomization. Results: Among 282 evaluable high-risk women enrolled from November 2016 to March 2020, mean age was 57 years (SD, 9.9), including 59% white, 14% black, 21% Hispanic, and 6% other. Mean 5-year invasive breast cancer risk was 2.98% (SD, 1.42), including 67% of women with benign breast disease and 64% with a first-degree family history of breast cancer. Comparing the intervention and control arms at 1 month, there were significant differences among high-risk women in accurate breast cancer risk perceptions (56% vs. 39%, p=0.017), adequate chemoprevention knowledge (49% vs. 27%, pConclusions: With short-term follow-up, exposure to our decision support tools was associated with improvement in decision antecedents (accurate breast cancer risk perceptions, adequate chemoprevention knowledge) and decision quality (increased informed choice, reduced decision conflict). However, actual chemoprevention uptake in both arms remained low at less than 5%. Future research should focus on targeting high-risk women with LCIS or atypical hyperplasia and better incorporating decision support into clinic workflow through EHRs and patient portals. Citation Format: Katherine D Crew, Gauri Bhatkhande, Thomas Silverman, Tarsha Jones, Jennie Mata, Ashlee Guzman, Ting He, Jill Dimond, Rita Kukafka. Randomized controlled trial of decision support tools for patients and providers to increase breast cancer chemoprevention [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS8-05.