World Blood Cancer Day is observed worldwide every May 28 to highlight the importance of blood stem cell donation in saving the lives of blood cancer patients. Established in 2014 by DKMS, an international nonprofit organization founded in Germany, the day commemorates the organization’s founding anniversary and aims to promote donor registries. Blood cancers, which include leukemia, lymphoma, and myeloma, affect blood cell production and function, and can be treated with various therapies, including hematopoietic stem cell transplantation (HSCT). Finding a matching donor for HSCT can be challenging due to the need for a close match of human leukocyte antigens (HLA). People can participate by registering as blood stem cell donors, donating to related organizations, hosting donor drives, or spreading awareness on social media using specific hashtags. DKMS has grown to become the largest stem cell donor registry globally, with chapters in multiple countries.