Simplify the following text for a Grade 7 native English-speaking person.
Original: The word leukemia , which means ` white blood ' , is derived from the disease 's namesake high white blood cell counts that most leukemia patients have before treatment .
Simplified: Leukemia or leukemia is a cancer of blood and bone marrow . When a person has leukemia , the body makes too many white blood cells ( leukocytes ) .