Chapter 18: Hairy Cell Leukemia

Epidemiology

Pathology

Peripheral blood findings at diagnosis

1. Pancytopenia: 50%

2. “Leukemic” phase with a WBC >1000/mm³: 10–20%

3. Monocytopenia

4. Hairy cells identified in most patients, but the number is usually low and may be difficult to identify in the peripheral blood because of low numbers and staining technique

Bone marrow findings at diagnosis

1. Hypercellularity

2. Hairy cell infiltration: diffuse, patchy, or interstitial

   1. Diffuse infiltration: Often results in complete effacement of bone marrow

   2. Patchy infiltration: Subtle small clusters of hairy cells present focally or throughout the bone marrow

   3. Interstitial infiltration: Hairy cells do not form well-defined discreet aggregates, but merge almost imperceptibly with surrounding normal hematopoietic tissue

3. Hairy cell nuclei are usually round, oval, or indented, and are widely separated from each other by abundant clear or lightly eosinophilic cytoplasm. Rarely, hairy cells can be convoluted or spindle shaped

4. Extravasated blood cells create blood lakes in the bone marrow similar to those observed in the spleen

5. Mast cells are often numerous

6. Reticulin stain of the bone marrow almost always shows moderate to marked increase in reticulin fibers

7. Approximately 10–20% of patients show a hypocellular bone marrow

Immunophenotyping, cytogenetics, and molecular diagnostic studies

1. Cytochemical studies: Tartrate-resistant acid phosphatase (TRAP) stain. However, TRAP is not specific for HCL

2. Hairy cell immunophenotype: CD19(+), CD20(+), CD22(+), CD79B(+), CD5(−), CD10(−), CD11C(+), CD25 Sub(+), FMC(+), CD103(+), CD45(+)

3. Clonal cytogenetics: Abnormalities in approximately two-thirds of patients. Chromosomes 1, 2, 5, 6, 11, 14, 19, and 20 are most frequently involved. Chromosome 5 is altered in approximately 40%, most commonly as a trisomy 5, pericentric inversion, and interstitial deletions involving band 5q13. However, the identification of cytogenetic abnormalities in a patient with a definite diagnosis of HCL is usually not important as it does not influence, as far as is currently determined, prognosis or therapy

Bartl R et al. Am J Clin Pathol 1983;79:531–545

Brunning RD et al. Atlas of Tumor Pathology, 3rd Series, Fascicle 9. Washington DC, AFIP, 1994; pp 277–278

Burke JS et al. Am J Clin Pathol 1978;70:876–884

Burke JS et al. Semin Oncol 1984;11:334–346

Cornfield DB et al. Am J Hematol 2001;67:223–226

Ellison DJ et al. Blood 1994;84:4310–4315

Flandrin G et al. Semin Oncol 1984;11(4 Suppl 2):458–471

Golomb HM et al. Ann Intern Med 1978;89(Part 1):677–683

Haglund U et al. Blood 1994;83:2637–2645

Hakimian D et al. Blood 1993;82:1798–1802

Hanson CA et al. Am J Surg Pathol 1989;13:671–679

Hounieu H et al. Am J Clin Pathol 1992;98:26–33

Katayama I. Hematol Oncol Clin North Am 1988;2:585–602

Kluin-Nelemans HC et al. Blood 1994;84:3134–3141

Kroft SH et al. Blood Rev 1995;9:234–250

Lee WM, Beckstead JH. Cancer 1982;50:2207–2210

Robbins BA et al. Blood 1993;82:1277–1287

Sausville JE et al. ...