What is Chronic Lymphocytic Leukemia (CLL)?

• A. A malignant B lymphocyte clone that avoids apoptosis and crowds the bone marrow, leading to pancytopenia.
• B. A malignant T lymphocyte clone causing hypercellular bone marrow.
• C. A plasma cell neoplasm causing osteolytic lesions.
• D. A myeloid leukemia with granulocytic proliferation.

Answer: (A)

Chronic lymphocytic leukemia is a malignancy of mature B lymphocytes that resist normal cell death. As these malignant B cells expand, they accumulate in the bone marrow and in the blood, crowding out normal hematopoietic cells. That crowding reduces production of other blood cells, so advanced disease can present with pancytopenia. This description highlights the B-cell clone, its survival advantage, and the marrow replacement that leads to cytopenias.

The other scenarios describe different diseases: a T-cell clone would point to a T-cell leukemia/lymphoma, a plasma cell neoplasm with bone damage suggests multiple myeloma, and a myeloid leukemia implies a proliferation of myeloid lineage cells rather than mature B lymphocytes.