When surgeons removed a cancerous tumor called a liposarcoma from Dan Ratliff’s pelvis, they also removed an artery and vein in his leg that were blocking their access to the tumor. Dan lost a great deal of blood during the 16-hour surgery, and received 12 units of donated blood.

Each day, cancer patients at MD Anderson need about 200 units of red blood cells and 600 units of platelets. However, because schools have been closed...