Yervoy (ipilimumab) is a biologic drug used to treat advanced melanoma, a type of skin cancer. According to the sources provided, the patent for Yervoy was set to expire in the United States on March 25, 2022 [1]. However, the expiration date may have changed since the sources were published.

Yervoy is manufactured by Bristol-Myers Squibb (BMS), a pharmaceutical company that has faced several patent expirations in recent years [2]. In its 2015 annual report, BMS stated that it expected to lose exclusivity for Yervoy in the United States in 2022 [3].

Patent expiration means that other companies can start producing generic versions of the drug, which can lead to increased competition and lower prices for consumers. However, biologic drugs like Yervoy are more complex than traditional small-molecule drugs, and the process for approving biosimilars (the equivalent of generic versions) is still evolving.

In conclusion, based on the sources provided, Yervoy's patent was expected to expire in the United States on March 25, 2022. However, it is important to note that this information may have changed since the sources were published.

Sources:
[1] https://www.drugpatentwatch.com/p/biologics/tradename/YERVOY
[2] https://www.fiercepharma.com/special-report/top-15-blockbuster-patent-expirations-coming-decade
[3] https://www.sec.gov/Archives/edgar/data/14272/000001427216000288/bmy-20151231x10xk.htm