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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
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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