Background: Biosimilar drugs, defined as biologic products with no clinically significant differences in quality, efficacy and safety compared to approved reference products have gained increasing adoption based on studies projecting significant cost savings[1]. Real world evaluation of biosimilar related cost savings and adoption is however still limited. We prospectively evaluate cost savings generated by transitioning to biosimilar monoclonal antibodies in a community based oncology practice. Methods: In July 2020, a process for transitioning patients to biosimilar equivalents of Rituximab, Trastuzumab and Bevacizumab was implemented in a community based oncology practice. Provider adoption was facilitated by monthly oncology pharmacy governance meetings that allowed provider participation and feedback followed by defaulting the preferred biosimilar product in oncology chemotherapy software (Epic Beacon, Epic Systems, Verona, WI). The treatment templates allowed for care personalization by listing reference products that could be chosen if desired. Cost savings achieved by switching to biosimilars was calculated by subtracting the actual spending on the biosimilar product from projected acquisition cost of the branded reference product (Table). Biosimilar adoption, defined as amount of biosimilar drug used over total amount of the drug ordered was also calculated. Results: Between July 2020 and April 2021, transitioning to biosimilar products for Rituximab, Bevacizumab and Trastuzumab resulted in net savings of $268,194.64, $285,251.89 and $274,359.51 respectively. Actual spending on Rituximab biosimilar product was $726,476.10 against a projected spending of $994,670.74 on the branded reference product. Actual spending on Bevacizumab biosimilar product was $1,254,977.30 against a projected spending of $1,540,229.19 on the branded reference product. Actual spending on Trastuzumab biosimilar product was $1,218,641.60 against a projected spending of $1,493,001.11 on the branded product. Average biosimilar utilization between October 2020 and April 2020 has been 92%, 100% and 98% for Rituximab, Bevacizumab and Trastuzumab respectively. Conclusions: Significant cost-savings can result from widespread utilization of biosimilar drugs in community oncology practices. References: Mulcahy, A.W., J.P. Hlavka, and S.R. Case, Biosimilar Cost Savings in the United States: Initial Experience and Future Potential. Rand Health Q, 2018. 7(4): p. 3.