Professional and Linguistic Assessments Board (PLAB) Practice Exam

Which histological feature is characteristic of Chronic Myeloid Leukemia (CML)?

1. Granulocyte without blast cells

2. Increased eosinophils

3. Presence of myeloblasts

4. Lymphoid hyperplasia

The correct answer is: Granulocyte without blast cells

In Chronic Myeloid Leukemia (CML), one of the hallmark histological features is the presence of numerous mature granulocytes, which can be observed without an abundance of blast cells. This reflects the nature of the disease, where the bone marrow produces a higher number of myeloid lineage cells, particularly granulocytes, due to the dysregulation associated with the Philadelphia chromosome (a specific genetic alteration present in most CML cases). Granulocytes become the most prominent cell type found in the peripheral blood and bone marrow during the chronic phase of the disease. The lack of significant numbers of blast cells is also a distinguishing feature that helps differentiate CML from acute myeloid leukemia, which is characterized by a higher percentage of myeloblasts and immature cells. In contrast, other features such as increased eosinophils are less specific to CML and can occur in various other conditions. The presence of myeloblasts typically indicates acute leukemias rather than chronic forms. Lymphoid hyperplasia is more associated with various lymphoproliferative disorders and does not represent the myeloid involvement seen in CML. Thus, the presence of granulocytes without an abundance of blast cells is a key feature that accurately represents the