Yervoy (ipilimumab) is a drug used to treat certain types of cancer. The patent for Yervoy was initially set to expire on March 25, 2019, according to DrugPatentWatch [1]. However, the patent was extended through a supplementary protection certificate (SPC) in Europe, which extends the patent for up to five years after the expiration of the original patent [3]. The SPC for Yervoy was granted on March 25, 2014, and will expire on March 25, 2024 [3]. It is important to note that the patent laws and regulations can vary between countries, and therefore the patent expiry date may differ depending on the region.

According to the SEC filing of Bristol-Myers Squibb, the manufacturer of Yervoy, the patent for Yervoy in the United States was set to expire in 2022 [2]. However, it is unclear whether this is the original patent expiration date or if it includes any extensions or SPCs.

In summary, the patent for Yervoy initially expired on March 25, 2019, but it was extended through an SPC in Europe, which will expire on March 25, 2024 [1][3]. The patent expiration date in the United States is unclear, but according to Bristol-Myers Squibb's SEC filing, it is set to expire in 2022 [2]. It is important to note that patent laws and regulations can vary between countries, and therefore the patent expiry date may differ depending on the region.

Sources:
[1] https://www.drugpatentwatch.com/p/biologics/tradename/YERVOY
[2] https://www.sec.gov/Archives/edgar/data/14272/000001427216000288/bmy-20151231x10xk.htm
[3] https://single-market-economy.ec.europa.eu/industry/strategy/intellectual-property/patent-protection-eu/supplementary-protection-certificates-pharmaceutical-and-plant-protection-products_en