SCYM Clinical Applications 3 — Questions and Answers
Question 1: A pleural effusion specimen shows a predominant population of T cells with CD4+/CD8- phenotype and aberrant loss of CD7. What does CD7 loss suggest?
- T-cell lymphoma involvement (Correct answer)
- Reactive benign effusion
- NK cell predominance
- Myeloid sarcoma
Correct answer: T-cell lymphoma involvement
Aberrant loss of pan-T-cell antigens such as CD7 in a T-cell population is a hallmark of T-cell lymphoma rather than a reactive process.
Question 2: In the diagnosis of systemic mastocytosis, which immunophenotypic aberrancy is most diagnostic on mast cells?
- Aberrant CD25 and/or CD2 expression (Correct answer)
- Loss of CD117 (c-kit)
- CD34 coexpression
- Downregulation of CD45
Correct answer: Aberrant CD25 and/or CD2 expression
Neoplastic mast cells in systemic mastocytosis aberrantly express CD25 and/or CD2, which are absent on normal mast cells.
Question 3: Which marker combination best identifies natural killer (NK) cells in peripheral blood by flow cytometry?
- CD56+/CD16+/CD3- (Correct answer)
- CD3+/CD56+/CD16-
- CD19+/CD56+/CD16+
- CD56+/CD3+/CD8+
Correct answer: CD56+/CD16+/CD3-
Mature NK cells are defined by CD56 and CD16 positivity with absence of CD3, distinguishing them from NKT cells.
Question 4: In acute myeloid leukemia (AML), which immunophenotype is associated with acute promyelocytic leukemia (APL/AML-M3)?
- CD33+/CD13+/HLA-DR-/CD34- (Correct answer)
- CD34+/CD117+/HLA-DR+/CD33+
- CD64+/CD14+/CD11b+/CD34-
- MPO-/CD33+/CD56+/CD34+
Correct answer: CD33+/CD13+/HLA-DR-/CD34-
APL blasts are typically CD33+/CD13+ but characteristically lack HLA-DR and CD34, which is diagnostically important.
Question 5: For minimal residual disease (MRD) detection in B-ALL, which immunophenotypic combination is most used as a leukemia-associated immunophenotype (LAIP)?
- Aberrant CD66c or CD45 dim with TdT+/CD10+/CD19+ (Correct answer)
- Normal B-cell maturation stages only
- CD3+/CD5+/CD1a+ combination
- Loss of CD34 on all blast populations
Correct answer: Aberrant CD66c or CD45 dim with TdT+/CD10+/CD19+
LAIPs in B-ALL commonly include aberrant expression of myeloid antigens like CD66c or abnormal CD45 levels within the immature B-cell gate.
Question 6: Which flow cytometric finding is most indicative of myelodysplastic syndrome (MDS) in bone marrow analysis?
- Aberrant myeloid maturation with CD13/CD16 asynchrony (Correct answer)
- Increased CD34+ cells above 20% of marrow cells
- Monoclonal B-cell population with dim surface Ig
- Hypergranular mast cell infiltration
Correct answer: Aberrant myeloid maturation with CD13/CD16 asynchrony
MDS is characterized by dysynchronous maturation patterns in myeloid cells, particularly aberrant CD13 vs. CD16 expression along the neutrophil maturation pathway.
Question 7: When analyzing cerebrospinal fluid (CSF) by flow cytometry, which technical consideration is most critical for accurate results?
- Processing within 1-2 hours to prevent cell degradation and loss of viability (Correct answer)
- Using a minimum of 1 mL sample volume
- Fixation immediately upon collection
- Centrifugation at high speed before staining
Correct answer: Processing within 1-2 hours to prevent cell degradation and loss of viability
CSF cells are fragile and deteriorate rapidly, so samples must be processed promptly—ideally within 1-2 hours—to maintain cell integrity and antigen expression.
SCYM Clinical Applications 3
A pleural effusion specimen shows a predominant population of T cells with CD4+/CD8- phenotype and aberrant loss of CD7.
What does CD7 loss suggest?