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B-Acute Lymphoblastic Leukemia Masquerading as Multifocal Langerhans Cell Histiocytosis: a Diagnostic Paradigm Shift
Insights
A rare pediatric cancer case highlights a diagnostic pitfall: B-cell acute lymphoblastic leukemia (B-ALL) can mimic Langerhans cell histiocytosis (LCH) on imaging. Molecular testing confirmed B-ALL with a KRAS mutation, revealing a new mechanism for bone destruction.
Area of Science:
- Pediatric Oncology
- Hematology
- Diagnostic Pathology
Background:
- A challenging case of B-cell acute lymphoblastic leukemia (B-ALL) in a child mimicked multifocal Langerhans cell histiocytosis (LCH).
- This diagnostic mimicry presented a significant pitfall in pediatric oncology.
- The patient, a 6-year-old girl, exhibited symptoms of progressive back pain.
Background:
This report describes a diagnostically challenging case of B-cell acute lymphoblastic leukemia (B-ALL) perfectly mimicking multifocal Langerhans cell histiocytosis (LCH), revealing a critical diagnostic pitfall in pediatric oncology.
Methods:
A 6-year-old girl presented with progressive back pain. MRI showed multilevel vertebral collapse (T11-L2) with classic LCH features, while PET-CT revealed disseminated hypermetabolic bone lesions (SUVmax 2.7). Comprehensive pathology included immunohistochemistry (CD79a, TdT, CD1a, Langerin) and next-generation sequencing.
Results:
Despite typical LCH imaging, immunohistochemistry demonstrated CD79a⁺/TdT⁺ B-lymphoblasts without CD1a/Langerin expression. Molecular analysis identified a pathogenic KRAS p.Gly13Asp mutation (VAF 1.5%), confirming B-ALL. This represents the first molecularly confirmed case of KRAS-mutated B-ALL mimicking LCH radiographically.
Conclusions:
This case mandates: 1) routine TdT staining for LCH-like lesions, 2) recognition of KRAS-driven osteolysis as a novel B-ALL mechanism, and 3) implementation of molecular profiling in atypical osteolytic cases. It highlights the need for integrated diagnostic approaches combining imaging, pathology, and molecular techniques in pediatric bone lesions.
