Blood Cancer Blood cancer is a type of cancer that affects the production and function of blood cells. It usually starts in the bone marrow, where blood is made, and disrupts the normal development of blood cells—mainly white blood cells, which are key to fighting infections. The main types include leukemia, lymphoma, and multiple myeloma. These cancers can weaken the immune system, cause fatigue, and lead to frequent infections, bleeding, or anemia. Early diagnosis and treatment are crucial for better outcomes