Unraveling enigmatic peripheral blood findings in a rare case of gamma-delta T-cell acute lymphoblastic leukemia

Gamma-delta T-cell acute lymphoblastic leukemia (γδ T-ALL) is an uncommon and aggressive variant of T-cell leukemia characterized by the proliferation of immature T-cells expressing γδ T-cell receptors. Here, we present a case of a 16-year-old male with γδ T-ALL exhibiting complex clinical and peripheral blood findings. Histopathological examination of bone marrow further confirmed the leukemic nature of the condition, with a markedly hypercellular marrow infiltrated by abnormal lymphoid cells showing blast morphology. Immunophenotyping of these γδ-positive cells provided crucial diagnostic insights, including negativity for CD48, strong positivity for CD99, and positivity for TdT in a subset of cells, leading to the diagnosis of γδ T-ALL. Notably, cytogenetic analysis identified MLLT4(ADFN)/MLL(KMT2A) fusion and a TP53 deletion. The diagnostic process highlighted the challenges in differentiating γδ T-ALL from other T-cell neoplasms and underscored the importance of extended immunophenotyping for accurate diagnosis.