Assay-aware flow-cytometric interpretation of relapsed B-cell precursor acute lymphoblastic leukemia after sequential CD19- and CD22-directed therapy: A case report.
Fangxiong Zheng, Juan Dong, Xiaocui Cao et al.
✦ AI-curated · Sources linked
Case in brief
A 73-year-old woman with B-cell precursor acute lymphoblastic leukemia developed marrow relapse after blinatumomab exposure. Relapse blasts expressed cytoplasmic CD19 and CD79a but lacked surface CD19; they also showed weak surface CD22 and CD13/CD33, without cytoplasmic MPO, CD14, or CD64. The findings supported B-cell precursor leukemia with aberrant myeloid-associated antigen expression, not mixed-phenotype acute leukemia. After INO-based salvage, marrow contained 0.5% blasts and a 0.007% abnormal population, approximately 30 events—above the assay’s detection limit but below its quantification limit. At later assessment, no previously identified abnormal population was detected under the reported assay conditions.
What made this case unusual
The case highlights discordance between cytoplasmic and surface CD19 after sequential antigen-directed therapy, alongside a very low-event posttreatment population whose surface CD22 was not detected. The population was detectable but below the assay’s quantification limit, making qualitative rather than quantitative interpretation important.
Diagnostic / clinical pearl
After antigen-directed therapy, distinguish cytoplasmic antigen findings used for lineage assignment from surface antigen expression relevant to therapeutic targets. Describe populations below the assay’s quantification limit qualitatively, and avoid inferring lineage switch or treatment causality from a single sample.