CML is cancer of WBCs that begins in the bone marrow (see Figure 6–1). When cancerous cells appear in the bone marrow, they multiply rapidly and begin to crowd out the normal cells, particularly red blood cells (RBCs). When this happens, anemia may occur. After accumulating in the bone marrow, cancerous WBCs spill over into the blood and invade other organs, such as the spleen.

Figure 6–1: CML is a disease of myeloid cells