Background: Checkpoint inhibitors have revolutionized the treatment of several cancers since the first Food and Drug Administration (FDA) approval in 2014. Yet the cost of these drugs remains high, with implications for patient access and healthcare sustainability. We assessed pricing trends for drugs targeting program death-ligand 1 (PD-L1) or programmed cell death protein 1 (PD-1) from 2016-2023. Methods: This study included 6 PD-L1 or PD-1 inhibitors approved through 2019. Quarterly Medicare Part B spending limits, which are based on the average sales prices of drugs from manufacturers to wholesalers or direct purchasers, were collected from public files. To directly compare drugs, prices were converted to prices per month (28 days), based on the FDA-labeled dosage and frequency for metastatic non-small cell lung cancer (NSCLC), a common cancer for which each drug was approved. Prices were adjusted to 2023 dollars using the consumer price index for all urban consumers. Results: In 2016, monthly prices for pembrolizumab ($15,604) and nivolumab ($15,814) were similar. Prices for these 2 drugs and avelumab, approved in 2017, remained within 5% of each other throughout the study period. Three other drugs (cemiplimab, atezolizumab, and durvalumab) were approved from 2016-2018 and had prices 3%-20% lower than the other 3 drugs (Table). Inflation-adjusted prices for all drugs remained stable from 2016-2019 and decreased from 2020-2023, corresponding with a period of higher inflation. In 2023, monthly prices for the 6 drugs ranged from $11,961 (durvalumab) to $15,043 (pembrolizumab). From 2016-2023, inflation-adjusted prices decreased, by an average of 0.7% (pembrolizumab) to 4.8% (cemiplimab) per year. Conclusions: Although the FDA approved 6 mechanistically similar PD-1 or PD-L1 inhibitors from 2014-2018, prices remained generally unchanged during those years and through 2023, with slight declines in real prices attributable to post-COVID consumer inflation. Competition among these brand-name cancer drugs did not meaningfully affect prices. Regulators should investigate why price competition has not emerged, and policymakers should grant more opportunities to negotiate lower prices for patients and the health care system, as is being rolled out this year in Medicare following passage of the Inflation Reduction Act.

*First quarter that prices for all drugs were available.

**Based on compound annual growth rate between first price and last price in the study period.