Cancer Biologics Utilization After Biosimilar Entry and Financial Implications For Payers and Patients

Importance: Biosimilars are highly similar to originator biologics and were introduced to increase market competition, lower the price of biologics, and expand patient access by improving affordability. By the end of 2024, three anticancer biologics have experienced biosimilar entry in the US (bevacizumab, rituximab, and trastuzumab), underscoring the need to evaluate their financial implications for payers and patients. Objective: To assess market dynamics and examine financial implications associated with biosimilar use patterns among patients who received bevacizumab, rituximab, or trastuzumab. Design, Setting, and Participants: This retrospective cohort examined price and market share trends and payer and patient costs after biosimilar entry. It used data from the Merative MarketScan commercial database and Medicare database from July 2019 to December 2024. Based on use patterns within 12 months of treatment initiation, patients were categorized into 4 groups: those who exclusively used biosimilars, exclusively used the reference product (ie, originator biologics), switched from the reference product to biosimilars, and switched from biosimilars to the reference product. Data were analyzed between September 2025 and March 2026. Main Outcomes and Measures: The primary study outcomes were average sales price (ASP), market share of reference products, and mean monthly payer and out-of-pocket costs within the study period. Results: Among 14 655 patients in this study, the mean (SD) age was 57 (13) years, 9985 (68.1%) were female, and the most common cancers were breast cancer (5182 [35.4%]), lymphoma (4320 [29.5%]), and colorectal cancer (1998 [13.6%]). A total of 8710 patients (59.4%) exclusively used biosimilars, 4760 (32.5%) exclusively used the reference product, 1015 (6.9%) switched from the reference product to biosimilars, and 170 (1.2%) switched from biosimilars to the reference product. After biosimilar entry, the ASP of the 3 reference products declined by an average of 3.8% annually. Their market share decreased 30% annually in commercial insurance and 31.5% in the Medicare Part B market. Compared with patients who only used the reference product, those who only used biosimilars rendered a $3820 lower mean monthly payer cost and $39.50 lower mean monthly out-of-pocket cost. Conclusions and Relevance: The results of this cohort study suggest that biosimilar entry was associated with lower ASP and reduced market share for reference biologics in oncology. Market competition introduced by biosimilars was also associated with lowered payer costs and reduced patient financial burden.