Thank you to everyone who participated in this challenging case. While the “cup-like” nuclear features sparked an excellent debate regarding myeloid versus lymphoid lineages, the final diagnosis was confirmed through immunophenotyping.

The patient, a newly turned 18-year-old, presented on Christmas Day with a classic triad of acute leukaemia symptoms: malaise (from anaemia), spontaneous bruising (from thrombocytopenia), and deep bone pain. The latter is a frequent finding in paediatric and young adult ALL, caused by the rapid expansion of the bone marrow cavity by malignant lymphoblasts.

The Diagnosis: B-cell Acute Lymphoblastic Leukaemia (B-ALL)

The laboratory data revealed a massive leucocytosis (81.25 x 10⁹/L) with 78% circulating blasts. While morphology provided the first clues, Flow Cytometry provided the definitive answer.

To confirm the lineage, the blasts were analysed for specific surface and cytoplasmic markers. The profile was diagnostic for B-ALL:

• Lineage Specific: Strong expression of CD19, CD22, and CD79a.
• Maturity Markers: Positive for TdT (Terminal Deoxynucleotidyl Transferase) and CD10 (CALLA).
• Myeloid Exclusion: Completely negative for Myeloperoxidase (MPO), CD13, and CD33.

In B-ALL, the bone marrow becomes “packed” with lymphoblasts. This increased intraosseous pressure, combined with the release of inflammatory cytokines and potential cortical bone involvement, leads to the deep, aching bone pain that often precedes the haematological diagnosis in young patients.