Background: Pegfilgrastim is a key supportive care agent in oncology patients, providing significant febrile neutropenia prophylaxis for patients on chemotherapy. However, pegfilgrastim also accounts for 5.3% of the total cost of cancer care for all patients in the Oncology Care Model (OCM). Fluctuations in the cost or quantity of pegfilgrastim can have significant impact on a practice’s performance under OCM. One such cost fluctuation is the introduction of biosimilars to the marketplace. This study seeks to understand how CMS reimbursement for pegfilgrastim has been impacted by the introduction of two pegfilgrastim biosimilars into the market. Methods: We tracked average CMS reimbursement for pegfilgrastim (Neulasta, Udenyca and Fulphila) from 7/1/2016 through 6/30/2019. We compared the average reimbursement and the average change in reimbursement before and after the introduction of biosimilars. Results: Prior to the introduction of biosimilars, the Medicare Part B reimbursement (80% of ASP +6%) of pegfilgrastim increased at a steady rate of $292 per year through the first 30 months of the OCM program, resulting in an average reimbursement of $3636 per administration in Q3 2018. However, since the introduction of biosimilars, average pegfilgrastim reimbursement has held steady, averaging $3543 for the time period from 7/1/2018 through 6/30/2019. The change in reimbursement has decreased from $292/year to -$93/year. Conclusions: In 2018, 88,847 Medicare patients received pegfilgrastim, resulting in $1.39 billion in Medicare reimbursement. Assuming that the patterns we’ve detected in our OCM data sample can be applied to the general Medicare population, we have estimated that the introduction of biosimilars resulted in a $4.8 million in savings (1.39%) compared with what the total reimbursement would have been without biosimilars in the market in Q4 2018. This bending of the cost curve is projected to result in savings of $79.1M (5.7%) in 2019 and $157.9M (11.5%) in 2020. Importantly, most of this cost containment is not due to patients utilizing biosimilars. 90.6% of patients in Q2 2019 are still receiving branded pegfilgrastim. However, the introduction of biosimilars has caused even the branded agent to stabilize and possibly even drop net acquisition cost prices. Introduction of biosimilars has created enough pressure on the market to result in significant cost savings, increasing the overall value proposition of pegfilgrastim. This results in significant cost saving to CMS, and also makes it easier for practices participating in OCM to have successful financial outcomes.