Bone marrow
Where it is
Soft, spongy tissue inside bones. In adults, blood-forming (red) marrow is mainly in the pelvis, breastbone, ribs, spine, skull and the ends of the long bones.
What it does
Makes all blood cells from stem cells: red cells that carry oxygen, white cells that fight infection and platelets that stop bleeding. Billions of new cells are made every day.
Link to blood
The blood factory: every circulating blood cell starts here.
Why it matters during treatment
Leukemia starts in the marrow when immature cells (blasts) multiply out of control and crowd out normal blood-making — which is why anaemia, infections and bleeding can happen. A bone marrow sample (usually from the back of the hip bone) is used for diagnosis and to check response. Chemotherapy temporarily suppresses the marrow so counts fall and then recover; a stem cell transplant renews blood-making.
Related topics
In the glossary
Bone marrowStem cell (blood-forming)Haematopoiesis (blood formation)BlastBone marrow aspirationNadir (lowest point)