Post‐Transplant Aggressive <scp>NK</scp> ‐Cell Leukemia: De Novo Versus Lineage‐Shift With Recurrent Hepatosplenic T‐Cell Lymphoma in the Setting of Chronic <scp>EBV</scp> Viremia

The recurrence of hepatosplenic T-cell lymphoma (HSTCL) accompanied by aggressive NK-cell leukemia (ANKL) is exceedingly rare. An earlier report described a case of HSTCL with an NK-cell-like immunophenotype following treatment [1]. However, to our knowledge, the present report is the first documented instance of HSTCL recurrence co-occurring with ANKL and highlights the importance of morphological analysis and flow cytometry in the diagnostic work-up of a hematologic malignancy. A 59-year-old female patient was admitted in January 2024 with fever and abdominal pain unresponsive to antibiotic therapy. Laboratory tests revealed pancytopenia (ANC 1.31 × 109/L, hemoglobin 82 g/L, and platelet count 25 × 109/L). Peripheral blood samples were positive for Epstein–Barr virus (EBV) DNA (8.69 × 103 copies/mL) and anti-liver-kidney microsomal antibody. Physical examination identified hepatosplenomegaly. Liver biopsy revealed diffuse infiltration of abnormal cells within the hepatic sinusoids, with negative EBV in situ hybridization staining. Bone marrow (BM) smears showed atypical lymphoid cells with faint nucleoli and agranular cytoplasm (Figure 1A). Flow cytometry detected abnormal T cells expressing CD2, CD7, CD56 (bright), surface CD3 (sCD3), and TCRγδ, but lacking CD5, TCRαβ, and CD158e (Figure 1B). TCR-γ gene rearrangement confirmed T-cell clonality. The karyotype analysis revealed a normal chromosome complement of 46, XX[20]. Integrated findings met the diagnostic criteria for HSTCL as outlined in the 5th edition of the WHO Classification of Haematolymphoid Tumours. She subsequently received chemotherapy, achieving minimal residual disease (MRD) negativity in the BM. Despite persistent EBV DNA positivity, she proceeded with autologous stem cell transplantation (ASCT) as consolidation therapy. In August 2024, two months post-ASCT, she developed fever, and TCR-γ rearrangement again tested positive, suggesting relapse. BM smears identified a discrepant morphology compared to the lymphoma at diagnosis, with atypical cells exhibiting azurophilic granules (Figure 1C). Flow cytometry identified two abnormal cell populations: a small population of abnormal T lymphocytes, and a large population of abnormal NK cells (Figure 1D). The immunophenotype of the small T-lymphocyte cluster and the TCR-γ rearrangement were consistent with the initial diagnosis. The large NK-cell cluster expressed CD2, CD7, and CD56 (bright) but lacked sCD3, cytoplasmic CD3 (cCD3), CD5, and TCR. Notably, 88.65% of these cells expressed CD158e, meeting the diagnostic criteria for clonal NK cells [2]. The findings of granulated morphology, aggressive course, and persistent EBV positivity met the WHO diagnostic criteria for ANKL. The patient was diagnosed with relapsed HSTCL with concurrent ANKL. She succumbed to hemorrhagic shock from splenic rupture 10 days after symptom onset. The cytoplasmic granules, which were not present at diagnosis, suggested a biological change in the neoplastic cells seen. The absence of cCD3 in new cells, along with the expression of CD158e, supported their lineage as NK cells. Flow cytometry, performed with a cCD3 antibody (clone SK7/Leu-4), which can distinguish between T-cell and NK-cell neoplasms [3], confirmed the NK-cell lineage, as cCD3 positivity indicates T-cell lineage, while its absence is consistent with NK-cell derivation. Persistent EBV positivity throughout the disease course reinforces the strong association between ANKL and EBV infection. Given existing evidence that EBV can infect hematopoietic stem cells, ASCT following EBV infection may fail to eradicate the virus, potentially increasing the risk of EBV-related malignancies. This case report has limitations. During the HSTCL and ANKL phases, molecular studies only detected TCR gene rearrangements, without testing for common T/NK-cell lymphoma gene mutations (e.g., STAT5B, STAT3). In the ANKL phase, due to rapid disease progression, karyotyping and EBV in situ hybridization were not performed. These tests could have helped differentiate between de novo ANKL and progression from the original HSTCL. Juanyu Ke conceived the study, analyzed and interpreted the data, and wrote the manuscript. Yiwen Zhou and Lei Chen reviewed and revised the manuscript. All authors contributed to the article and approved the submitted version. Reviewed and approved by Shenzhen Hospital of Southern Medical University Academic Ethics Committee. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.