Chemotherapy and radiation therapy may cause low blood cell count, Mayo Clinic states. Cancer may also be a direct cause of low blood cell count if the patient has blood and bone marrow cancer or cancer of another type that spreads to bone marrow.
Bone marrow is the site of blood cell production, and certain types of chemotherapy drugs and high doses of radiation therapy may damage it, Mayo Clinic advises. Exposing large body areas and large bones to radiation therapy is likely to cause enough damage to bone marrow to reduce blood cell levels. Some types of chemotherapy drugs destroy bone marrow cells, reducing the capacity of bone marrow to produce new blood cells.
Low blood cell counts may have significant consequences, including excessive bleeding, infections and anemia, Mayo Clinic warns. Excessive bleeding occurs due to a low platelet count; patients can lose large amounts of blood from small cuts and experience internal bleeding. Doctors may postpone further treatment and surgery until platelet counts normalize. An infection may develop due to a lack of white blood cells that normally fight it off, and only a slight infection is enough to delay further chemotherapy. Anemia results from a lack of red blood cells, and its symptoms include feeling short of breath and feeling fatigued. Occasionally, this feeling of fatigue is strong enough to require pausing treatment or reducing dosage.