Background: Angioimmunoblastic T-cell lymphoma (AITL) is a distinct subtype of peripheral T-cell lymphoma (PTCL) and accounts for 2% of all non-Hodgkin lymphomas. Its typical characteristics include an aggressive course, progressive lymphadenopathy, hepatosplenomegaly, systemic symptoms, anemia, hypergammaglobulinemia, and generally poor prognosis.

Methods: We describe a rare case in which the left inguinal lymph node was completely excised and biopsied one year ago. Based on histomorphology and immunohistochemistry, B-cell small lymphocytic lymphoma (CLL/SLL) was diagnosed. Routine bone marrow examination indicated the presence of immature lymphocytes; however, immunophenotyping showed no significant abnormal lymphocytes. One month ago, the patient developed swelling in the left lower limb, which gradually worsened. A fine-needle aspiration biopsy of the left inguinal lymph node revealed angioimmunoblastic T-cell lymphoma.

Results: The final diagnosis for this patient is a transformation from B-cell small lymphocytic lymphoma to angioimmunoblastic T-cell lymphoma (AITL) one year after the initial diagnosis.

Conclusions: In this report, we present a rare case of AITL. The aim is to enhance awareness among readers regarding the clinical, immunological, and phenotypic characteristics of various forms of AITL.