Introduction to Lineage Ambiguity

Establishing an accurate T-cell leukemia diagnosis remains a significant challenge for hematopathologists when neoplastic cells lose conventional markers. Neoplastic T cells occasionally lose surface CD3 (sCD3) and CD5. Simultaneously, they may acquire Natural Killer (NK) cell markers such as CD16, CD56, and CD94. This immunophenotypic shift can lead to the misclassification of T-cell lymphomas as NK-cell neoplasms, which carries distinct clinical and therapeutic implications.

Analysis of NK-like T-cell Neoplasms

A recent study reported on a series of seven mature T-cell leukemia and lymphoma cases that exhibited an NK-like immunophenotype. The cohort included cases of peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), T-large granular lymphocytic leukemia (T-LGLL), and hepatosplenic T-cell lymphoma (HSTCL). Furthermore, flow cytometry revealed that all cases were positive for CD56 and CD94. Four cases also expressed CD16. Crucially, these cells lacked surface T-cell markers like CD4, CD5, and sCD3. Consequently, the initial immunophenotype strongly mimicked true NK cells rather than T-lineage cells.

Optimizing T-cell Leukemia Diagnosis with Molecular Tools

To ensure a precise T-cell leukemia diagnosis, clinicians must utilize advanced molecular and immunohistochemical tools. In the reported cases, T-cell receptor (TCR) gene rearrangement analysis confirmed the T-lineage, as all cases demonstrated monoclonal TRG rearrangements. Moreover, immunohistochemical testing showed that BCL11B, a T-lineage-specific transcription factor, was expressed in all tested cases. Research suggests that BCL11B is highly sensitive and specific for T cells and is typically absent in NK cells. Therefore, BCL11B serves as a robust marker when surface T-cell receptors are absent.

Reliable Markers for Lineage Determination

In addition to TCR clonality, other features support T-lineage in the context of an NK-like phenotype. Cytoplasmic CD3 (cCD3) expression, detected via specific antibodies, remains a hallmark of T-lineage even when surface CD3 is lost. Similarly, the detection of TCRαβ, TCRγδ, or TRBC1 by immunohistochemistry can confirm the diagnosis. In summary, the integration of molecular clonality and lineage-specific proteins like BCL11B is essential for avoiding diagnostic pitfalls.

Frequently Asked Questions

How does BCL11B aid in T-cell leukemia diagnosis?

BCL11B is a transcription factor essential for T-cell commitment. Because it is highly specific to the T-lineage and absent in NK cells, its expression in a CD56-positive neoplasm strongly suggests a T-cell origin rather than an NK-cell origin.

Why do some T-cell lymphomas express NK-cell markers?

Neoplastic T cells can undergo immunophenotypic shifts, losing pan-T-cell antigens and gaining NK-cell markers like CD56 or CD94. This often occurs in specific subtypes like hepatosplenic T-cell lymphoma or during aggressive disease progression.

Is TCR gene rearrangement always required for diagnosis?

While not always mandatory, TCR gene rearrangement analysis is the gold standard for confirming clonality and lineage in cases where flow cytometry shows an ambiguous or NK-like immunophenotype.

Disclaimer: This content is for informational and educational purposes only and does not constitute medical advice or a professional relationship. Always seek the advice of a physician or other qualified health provider with any questions regarding a medical condition. Refer to the latest local and national guidelines for clinical practice.

References

Wang WJ et al. Mature T-cell leukemia/lymphoma with an NK-like immunophenotype: A report of 7 cases. Cytometry B Clin Cytom. 2026 Feb 20. doi: 10.1002/cyto.b.70020. PMID: 41721448.

Patel et al. Expression pattern and diagnostic utility of BCL11B in mature T- and NK-cell neoplasms. Pathology. 2022 Dec;54(7):857-865. doi: 10.1016/j.pathol.2022.04.012.

Alaggio R, et al. The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Lymphoid Neoplasms. Leukemia. 2022 Jul;36(7):1720-1748.