The case of T-ALL presenting with NK phenotype after COVID-19 vaccination.

NK-lymphoblastic leukemia/lymphoma (NK-LL) is an extremely rare hematopoietic tumor consisting of natural killer (NK) precursor cells, and their lineage overlaps with T-cells, making it challenging to diagnose. COVID-19 vaccination is recommended for people with a risk of aggravation such as cancer-bearing patients, including hematopoietic tumors. We present a 55-year-old man who had cervical lymph node swelling post vaccination for COVID-19. Hematological malignancy was suspected due to the presence of atypical lymphoid cells with an elevated IL-2R in laboratory data. Tumor cells were positive for CD7, CD56, cyCD3, and terminal deoxynucleotidyl transferase (TdT) evidenced through flow cytometry of the bone marrow and the lymph node. The histopathological findings showed monotonous tumor cell proliferation, the cells being positive for CD3 and TdT in the bone marrow and they were positive for CD3, TdT, and CD56 in lymph node. Even though these findings suggested NK-LL, clonal T-cell receptor (TCR) β gene rearrangement by Southern blot hybridization was observed in the bone marrow. TCRβ rearrangement led to the final diagnosis of T-cell lymphoblastic leukemia (T-ALL). The causal relationship between COVID-19 vaccination and carcinogenesis is not clear, and more cases need to be studied in order to elucidate the relationship between the two factors.