Have you heard about Leukemia?
Do you know what it is?

Leukemia is the cancer of the white blood cells, a situation in which your bone marrow churns out a large number of abnormal, infective white blood cells.

Your white blood cells are a part of your immune system which helps the body fight infection and other diseases, so when the bone marrow gives out infective white blood cells, it can lead to leukemia.