Assessing biosimilar entry in the market for biologic cancer drugs.

11162 Background: Biosimilars are biological drugs highly similar to and without clinically meaningful differences from their biological reference products. As of 2023, out of 39 biosimilars available in the US, 22 (56%) are indicated for cancer treatment (n=12) or supportive care (n=10). This study described the trends in uptake, pricing, and out-of-pocket (OOP) costs between 2014 and 2023. Methods: Using MarketScan claims data and Average Sales Price (ASP) data from the Centers for Medicare & Medicaid Services, we calculated quarterly ASP and the market share of reference products for treatment and supportive care biologics in the commercial and Medicare Part B markets, 2014 to 2023. We also estimated the average monthly out-of-pocket costs (deductible + copayment + coinsurance) before and after biosimilar entry. We identified biologics using Healthcare Common Procedure Coding System codes and adjusted costs to 2024 USD using the prescription drugs Consumer Price Index. Results: Analyses included 1,040,456 claims of 28 biological products (6 reference products and 22 biosimilars). On average, the ASP of reference products for treatment and support care decreased by 1.3% and 2.8% per quarter, respectively, after biosimilar entry. Market share of reference products declined over time after biosimilar entry, though the decline was smaller in the Medicare market than in commercial insurance market as of 2023 Q4. The average quarterly reduction ranged between 2.2% and 14.6% across reference products, with larger reduction for treatment drugs. Compared to monthly OOP averaging over 12 months before first biosimilar launch, monthly OOP costs of biologics (including reference and biosimilars) in 2023 fell for 4 reference drugs in the commercial market, and 5 in the Medicare market. Conclusions: Biosimilar entry has lowered the price and led to a substantial reduction in market share of biologic reference products, especially for cancer treatment drugs. Nevertheless, trends in OOP costs for biologics indicated biosimilars did not always lower financial burden for patients. Commercial insurance Medicare Part B Drug 1 st biosimilar entry Reference product ASP quarterly change Market share of reference product, 2023 Q4 (quarterly change) Mean monthly OOP before biosimilar entry Mean monthly OOP, 2023 Market share of reference product, 2023 Q4 (quarterly change) Mean monthly OOP before biosimilar entry Mean monthly OOP, 2023 Bevacizumab 2019 Q2 -0.61% 9.29%(-14.65%) $55.88 $47.07 17.67%(-10.91%) $23.31 $27.52 Rituximab 2019 Q4 -1.38% 14.91%(-13.62%) $96.28 $88.28 18.42%(-12.20%) $48.31 $36.90 Trastuzumab 2019 Q2 -1.91% 12.67%(-12.87%) $44.39 $44.71 15.39%(-11.73%) $25.37 $24.80 Epoetin alfa 2018 Q4 -2.04% 54.46%(-3.32%) $17.61 $25.76 62.22%(-2.60%) $17.75 $10.38 Filgrastim 2015 Q3 -0.01% 4.17%(-10.05%) $11.72 $10.76 2.27%(-11.86%) $7.40 $2.36 Pegfilgrastim 2018 Q2 -6.50% 65.13%(-2.23%) $65.92 $57.97 61.70%(-2.51%) $54.41 $30.36