ICCS e-newsletter CSISpring 2012

Weina Chen, MD, PhD

Medical Director, Hematopathology

Ameripath/Quest Diagnostics

Dallas, Texas

Case History

The patient is a 70-year old female presented with mild leukocytosis. She has no prior history of any significant diseases and is asymptomatic.

Complete blood count

WBC 10.70NE 50%LY 39.4%MO 9.3%EO 0.7%BASO 0.6%

RBC 4.41HGB 12.7HCT 37.7%MCV 85.5MCHC 33.70RDW 12.6PLT 211.0

Work-up and evaluation

Bone marrow (BM) aspirate and biopsy were procured.

Flow cytometric analysis was performed on marrow aspirate and results from selected 4-color tubes are provided for review.

Flow cytometric analysis

• Acquisition Beckman Coulter Epics XL (FCS2.0, System II)

• Analyzed by Paint-A-Gate software (adapted to Coulter)

• Tubes (FITC/PE/ECD/PC5)

– Tube 1: Kappa/lambda/45/19+20

– Tube 2: 5/19/45/10

– Tube 3 : 8/4/45/38

– Tube 4: 15/117/45/34

– Tube 5: 20/10/19/38

– Tube 6: FMC-7/23/5/19

– Tube 7: Kappa/Lambda/5/19

Tube 1: Kappa/lambda/45/19+20

Tube 1: Kappa/lambda/45/19+20

Tube 2: 5/19/45/10

Tube 3 : 8/4/45/38

Tube 4: 15/117/45/34

Tube 5: 20/10/19/38

Tube 6: FMC-7/23/5/19

Tube 7: Kappa/Lambda/5/19

[In addition, CD13-, CD33- (data not shown); Tdt not tested]

Key flow plots in this case

CD19(+)/CD20(+) B cells overall exhibiting a pattern of sequential maturation

Morphologic evaluation

Marrow infiltrated by abundant small to medium-sized lymphoid cells with mature morphologic features although nuclear irregularity/convolution and small cytoplasmic vacuoles observed in a few scattered lymphoid cells.

CD20 CD34CD79a

Tdt CD10

Immunohistochemical evaluation

A prominent CD79a(+) B-lymphoid hyperplasia of mostly CD10(+) B lymphocytes with increased Tdt(+) cells, some in clusters exceeding 3 or 4 cells

Questions…

• There is an expansion of B cells overall exhibiting a spectrum of maturation.

• Are these normal maturing B-cell precursors (hematogones) or B-lymphoblasts?

A few words on hematogones…

• Hematogones always express consistent, reproducible, complex spectrum of sequential antigen expression and lack aberrant antigen expression.

• This defines hematogones into three stages of maturation– Stage 1 hematogones express CD34, high levels of CD10 and CD38, a

moderate level of CD22, and absence of CD20.

– Intermediate stage 2 hematogones downregulate CD34 completely and CD10 partially, while increasing expression of CD22 and CD20.

– Stage 3 hematogones upregulate CD20 expression reaching the intensity of mature B cells, and CD10 and CD38 are slightly down-regulated with increasing expression of polytypic surface immunoglobulin light chains.

– Subsequently, these cells mature into CD20(+), CD10(-) mature B cells.

– CD5 is expressed on normal, polytypic B cells in a continuum, predominantly at later stages of maturation, specifically on stage 3 hematogones and mature B cells.

Comparison to a case with hematogone hyperplasia

A case with hematogone (HG) hyperplasia case (bottom plots):

Blue, mature B cells; Green, stage 2+3 HG; yellow, stage I HG

Comparison to a case with hematogone hyperplasia

A case with hematogone (HG) hyperplasia case (bottom plots):

Blue, mature B cells; Green, stage 2+3 HG; yellow, stage I HG

Questions…

• These B cells exhibit a spectrum of maturation reminiscent of hematogones and unusual for neoplastic lymphoblasts.

• Are these hematogones???

Answer…

• No• These are B-lymphoblasts.

• The key finding in this case (on BM sample)

– Cytogenetics: 46, XX, t(9;22)(q34;q11.2)[17]/46, XX [3]

– Positive FISH for t(9;22)/BCR-ABL1 in 79% of interphase cells

Answer…

• Differential diagnosis

– An early chronic myelogenous leukemia (CML) with background hematogone hyperplasia (but the usual morphologic features of CML not apparent)

– Lymphoid blast crisis of CML (but no history of CML)

– An early B-lymphoblastic leukemia with t(9;22)(q34;q11.2);BCR-ABL1

Favored Diagnosis

B-lymphoblastic leukemia with t(9;22)(q34;q11.2);BCR-ABL1

Based on the high percent of t(9;22) positive cells (~70%), the entire B-cell population or the majority of B cells including polytypic B cells seems neoplastic.

A few words on B-lymphoblastic leukemia with t(9;22)(q34;q11.2);BCR-ABL1

• The most frequently observed chromosomal abnormality in adult B-ALL (25% vs. 3-5% in children)

• Involving the ABL1 oncogene on chromosome 9 and the guanosine triphosphate–binding protein BCR on chromosome 22

• The resultant fusion protein having abnormal tyrosine kinase activity, leading to disturbances in proliferation, survival, and adhesion

• In about 70% of cases of BCR-ABL1+ B-ALL, the expressed protein being 190 kDa, rather than the 210 kDa typically seen in CML

• Associated with a poor prognosis in both children and adults

Unusual features in this case• Unusual presentation: close to normal CBC with differential at

presentation

• Unusual morphology: mature morphologic features with mild cytological atypia

• Unusual immunophenotype: maturation spectrum reminiscent of hematogones (with only subtle deviation)

• Unusual, indolent clinical course

– Follow-up BM in 5 months (with only imatinib mesylate tx)

• Close to normal CBC, asymptomatic

• Persistent, but decreased B-lymphoblasts (similar phenotype)

• RT-PCR: positive BCR-ABL1, p190, further supporting B-ALL

What are the clues to avoid misdiagnosis?

• No apparent causes for hematogone hyperplasia• Common causes for hematogone hyperplasia:

• Reactive conditions: AIDS, immune dysregulation, copper deficiency), BM involved by metastatic tumors• Regenerative conditions: post-chemotherapy and stem-cell transplant• Relatively high number of hematogones in children

• Subtle immunophenotypic deviation from hematogones• Less distinct “ladder” of CD45 on subsets of B cells• Tdt positive cells, some in clusters exceeding 3 or 4 cells

• The need to add new markers to distinguish hematogones from lymphoblasts

• CD81, CD123

Take home messages

• The immunophenotype of B-lymphoblasts is variable.

• While the majority of cases having distinct immunophenotypic aberration deviated from hematogones, rare cases with immunophenotypic feature reminiscent of hematogones do exist.

• Careful immunophenotypic analysis, clinical correlation for causes of hematogone hyperplasia, ancillary studies (cytogenetics, FISH/molecular studies) are the key elements to reach a correct diagnosis.

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