What is a disease of the bone marrow with malignant WBCs filling and bloodstream?

The disease is called leukemia.

Leukemia is a type of cancer that starts in the blood-forming tissue of the bone marrow. Leukemia cells are abnormal white blood cells that can't fight infection the way normal white blood cells do. As leukemia cells grow, they crowd out healthy blood cells, which can lead to anemia, bleeding, and infection.

There are four main types of leukemia:

- Acute lymphoblastic leukemia (ALL)

- Acute myeloid leukemia (AML)

- Chronic lymphocytic leukemia (CLL)

- Chronic myeloid leukemia (CML)

ALL and AML are most common in children, while CLL and CML are more common in adults.