Some cancers can cause leukopenia, especially if they involve the bone marrow. The most common culprit in acutely developing leukopenia is acute myeloid leukemia. When the diagnosis is suspected, acute myeloid leukemia patients should undergo a blood film analysis. This is a manual examination of the blood because the automated analyzer may falsely think that they have an elevated white blood cell count. The reason behind this is the presence of huge numbers of immature cells in their blood called blast cells. These cells invade the bone marrow and hinder the division and differentiation of other cells of the bone marrow causing deficiencies of all cells in the blood.
Another cancer that can cause the same problem is lymphoma. Lymphomas may also invade the bone marrow resulting in reduced formation of blood cells.