Leukemia is a form of cancer, and thusly the kind of Doctor Who specializes in it is called an "Oncologist".
However, this specific disease may have some cross talk with another specialty called hematology - the specialty concerning blood and diseases in blood. A person within this kind of specialty is called a "hematologist".
A person who studies blood and its diseases is called a hematologist. They specialize in diagnosing and treating disorders related to the blood, such as anemia, leukemia, and bleeding disorders.
The Person Who studies about mamals , he is called mamalogist....
A person who studies volcanoes is called a volcanologist.
A person who studies the grass and soil, etc. is called a Agrostologist
A person who studies or writes history is called a historian.
A person who studies the mind and behavior is called a psychologist.
A person who studies geology is a geologist.
A person who studies culture is called an anthropologist.
a person that studies gems is called a gemologist.
A person who studies bees is called an apiologist.
A person who studies philosophy is called a philosopher.
A person who studies the grass and soil, etc. is called a Agrostologist