Incidental Monoclonal B-Cell Lymphocytosis in an Older Woman
A 68-year-old woman has incidental lymphocytosis of 18 ×10^9/L on a routine CBC. Hb is 12.5 g/dL, platelets 180 ×10^9/L, and she has no lymphadenopathy or hepatosplenomegaly. The smear shows small lymphocytes and smudge cells. Flow cytometry shows CD19+, CD5+, CD23+, dim CD20, dim surface kappa, FMC7 negative, and CD200 positive. The laboratory reports a monoclonal B-cell population. The patient asks whether she needs treatment now and whether her daughter should be tested.
1. Interpret the flow cytometry and give the most likely diagnosis.
Read the worked answer
The immunophenotype is typical of chronic lymphocytic leukemia (CLL): CD19+, CD5+, CD23+, dim CD20, dim surface immunoglobulin, FMC7 negative, and CD200 positive. Because the absolute B-cell count is above the monoclonal B-cell lymphocytosis threshold of 5 ×10^9/L, this is CLL rather than MBL. The absence of lymphadenopathy, organomegaly, and cytopenias indicates early-stage disease. Smudge cells are supportive but not diagnostic. Correlate with the CBC and clinical exam, and document the blood count and nodal status for staging.
2. Which prognostic tests should be ordered, and why should treatment not be started based on them alone?
Read the worked answer
Order FISH for del(13q), del(11q), trisomy 12, and del(17p), plus TP53 sequencing and IGHV mutation status. These tests stratify risk and inform future therapy, especially before treatment with chemoimmunotherapy or targeted agents. However, early-stage asymptomatic CLL is managed with observation regardless of most prognostic markers. Treatment is indicated for progressive marrow failure, bulky or symptomatic lymphadenopathy or splenomegaly, systemic symptoms, or rapid doubling. Do not treat solely because del(17p) or unmutated IGHV is present.
3. What would make you reconsider mantle cell lymphoma, and what test would you add?
Read the worked answer
Reconsider mantle cell lymphoma if the cells are CD5+ but CD23 negative, FMC7 strongly positive, CD20 bright, or surface immunoglobulin bright, or if cyclin D1 is expressed. Mantle cell lymphoma often has t(11;14) and may be SOX11 positive. Add cyclin D1 immunohistochemistry and CCND1 FISH if morphology or flow is atypical. Distinguishing these entities matters because mantle cell lymphoma is managed differently and usually requires earlier systemic therapy.
4. What counseling should be given about treatment and family screening?
Read the worked answer
Explain that early-stage CLL is usually observed with periodic CBC and clinical review, often every 3 to 6 months initially. Counsel about infection risk, appropriate vaccinations, and reporting B symptoms or new adenopathy. Routine screening of her daughter is not recommended; familial clustering is uncommon and screening asymptomatic relatives is not standard. Advise the daughter to seek evaluation only if she develops symptoms or abnormal blood counts.