What term refers to a form of cancer that affects white blood cells?

The term that refers to a form of cancer affecting white blood cells is leukemia. This condition specifically involves the uncontrolled proliferation of abnormal white blood cells, which can interfere with the body's ability to fight infections. Leukemia primarily originates in the bone marrow but can spread to other areas of the body and is characterized by an elevated number of these atypical cells in the bloodstream.

In comparison, lymphoma, while also a cancer of the blood, primarily affects lymphocytes, which are a specific type of white blood cell that form part of the lymphatic system. Influenza and measles are viral infections and do not classify as cancers. Thus, understanding the definitions and implications of these terms clarifies why leukemia is the correct answer for this question.