anna fitzgerald's older sister, kate, suffers from acute promyelocytic leukemia, a cancer of the blood and bone marrow. when anna's parents learn about kate's diagnosis, they decide to conceive anna through artificial selection and in vitro fertilization because nobody in the family is a genetic match to donate organs to kate. once anna is born, her umbilical chord blood was used in treatments for kate to save her life. although the treatment was initially successful, kate relapsed (became sick again). since then, anna had been used as a donor for any other bodily substance needed to treat kate, who continues to swing between remission and relapse as she grows up.