Bone marrow, a semi-solid tissue found within the spongy or cancellous portions of bone, is mainly composed of hematopoietic cells, marrow adipose tissue, and supportive stromal cells. Hematopoietic cells are Cluster of differentiation 34 (CD34) positive. CD 34 is a sialomucin-family protein generally expressed on the surface of blood, endothelial, and bone marrow-derived progenitor cells. CD 34 protein is known to be involved in maintaining progenitor cells in an undifferentiated state.