PURPOSE Biosimilars are clinically equivalent to branded products yet cost significantly less. Interchangeability is a US Food and Drug Administration (FDA) designation that allows generic drugs to be substituted for reference drugs at the pharmacy, without a physician's consent. Currently, no oncologic biosimilar has FDA approval for interchangeability. METHODS Building on pharmacy auto-substitution processes with therapeutic interchange, Plan-Do-Study-Act methodology was used to automate conversions from reference biological products to Pharmacy and Therapeutics–/Physician-approved biosimilars. After establishing the baseline metrics, cycle 1 focused on full staff education (completed July 2020) with systematic pharmacy-driven biosimilar conversion initiated in September 2020 for rituximab, trastuzumab, and bevacizumab. Physician-initiated conversion of Neulasta biosimilar products was encouraged but not mandated. During cycle 2 (May 1, 2021-November 30, 2021), pharmacy-driven Neulasta biosimilar conversion was mandated. In cycle 3 (December 1, 2021-April 30, 2023), stakeholder education was reinforced and the sustainability of conversions was confirmed. RESULTS Systematic pharmacy-driven conversion to biosimilar products improved over cycles 1 and 2 from baseline: 1.8% to 90.3% for rituximab, 9.2% to 89.7% for trastuzumab, and 20.5% to 96.1% for bevacizumab. Physician-driven biosimilar conversion for Neulasta was lower at 12.7% through April 2021. Pharmacy-driven Neulasta biosimilar conversion was initiated during cycle 2, resulting in a conversion rate of 39.7%. The conversion rates remained sustainable through April 2023. CONCLUSION Pharmacy-driven auto-substitution of biosimilar products results in rapid and statistically significant biosimilar adoption. The pharmacy-based substitution approach was found to be far more effective than physician-driven substitution. Rapid conversion from branded products to FDA-approved biosimilar is feasible, measurable, and sustainable and can be scaled. Barriers to Neulasta conversion warrant further investigation.